Supplemental Nutrition in Container Culture (long post)

Bay City, MI(Zone 6a)

I've been studying fertilizing and plant nutrition as it relates to container culture for some time now. This subject has been discussed frequently, but in rather piecemeal fashion on the Container Gardening forum and forums related. So, prompted by a question about fertilizers in my mail, I decided to collect a few thoughts & share an individual's considered overview. I hope it leads to as much discussion and garners as much interest as the Container Soil post did. ;o)

Fertilizer Program - Containerized Plants

Let me begin with a brief and hopefully not too technical explanation of how plants absorb water from the soil and the nutrients/solutes that are dissolved in that water. Most of us remember from our biology classes that cells have membranes that are semi-permeable. That is, they allow some things to pass through the walls, like water and whatever is dissolved in it, while excluding other materials. Osmosis is a natural phenomenon that creates a balance (isotonicity) in pressure between liquids and solutes inside and outside the cell. Water and ionic solutes will pass in and out of cell walls until an equilibrium is reached and the level of solutes in the water surrounding the cell is the same as the level of solutes in the cell.

This process begins when the finest roots absorb water molecule by molecule at the cellular level from the surface of soil particles and transport it, along with its nutrient load, throughout the plant. I want to keep this simple, so I’ll just say that the best water absorption occurs when the level of solutes in soil water is lowest, and in the presence of good amounts of oxygen (this is where I get to plug a well-aerated and free-draining soil), ;o) but of course, when the level of solutes is very low, the plant is shorted the building materials (nutrients) it needs to manufacture food and keep its metabolism running smoothly, so it begins to exhibit deficiency symptoms.

We already learned that if the dissolved solutes in soil water are low, the plant may be well hydrated, but starving; however, if they are too high, the plant may have a large store of nutrients in the soil, but because of osmotic pressure, the plant may be unable to absorb the water and could die of thirst in a sea of plenty. When this condition occurs, and is severe enough (high concentrations of solutes in soil water), it causes fertilizer burn (plasmolysis), where plasma is torn from cell walls as the water inside the cell exits to maintain solute equilibrium with the water surrounding the cell.

Our job, because you will not find a sufficient supply of nutrients in a container soil, is to provide a solution of dissolved nutrients that affords the plant a supply in the adequate to luxury range, yet still makes it easy for the plant to take up enough water to be well-hydrated and free of drought stress. Electrical conductivity (EC) of the water in the soil is a reliable way to judge the level of solutes and the plant’s ability to take up water. There are meters that measure this conductivity, and for most plants the ideal range of conductivity is from 1.5 - 3.5 mS, with some, like tomatoes, being as high as 4.5 mS. This is more technical than I wanted to be, but I added it in case someone wanted to search "mS" or "EC". Most of us, including me, will have to be satisfied with simply guessing, but understanding how plants take up water and fertilizer and the effect of solute concentrations in soil water is an important piece of the fertilizing puzzle.

Now, some disconcerting news - you have listened to all this talk about nutrient concentrations, but what do we supply, when, and how do we supply them? We have to decide what nutrients are appropriate to add to our supplementation program, but how? Most of us are just hobby growers and cannot do tissue analysis to determine what is lacking. We can be observant and learn the symptoms of various nutrient deficiencies though - and we CAN make some surprising generalizations.

What if I said that the nutritional needs of all plants is basically the same and that one fertilizer could suit almost all the plants we grow in containers - that by increasing/decreasing the dosage as we water, we could even manipulate plants to bloom and fruit more abundantly? It’s really quite logical, so please let me explain.

Tissue analysis of plants will nearly always show NPK to be in the ratio of approximately 10:1.5:7. If we assign N the constant of 100, P and K will range from 13-19 and 45-70 respectively. I’ll try to remember to make a chart showing the relative ratios of all the other 13 essential nutrients that don’t come from the air at the end of what I write.

All we need to do is supply nutrients in approximately the same ratio as plants use them, and in adequate amounts to keep them in the adequate to luxury range at all times. Remember that we can maximize water uptake by keeping the concentrations of solutes low, so a continual supply of a weak solution is best. Nutrients don’t just suddenly appear in large quantities in nature, so the low and continual dose method most closely mimics the nutritional supply Mother Nature offers. If you decide to adopt a "fertilize every time you water" approach, most liquid fertilizers can be applied at ¾ to 1 tsp per gallon for best results. If you decide that’s too much work, try halving the dose recommended & cutting the interval in half. You can work out the math for granular soluble fertilizers and apply at a similar rate.

The system is rather self regulating if fertilizer is applied in low concentrations each time you water, even with houseplants in winter. As the plant’s growth slows, so does its need for both water and nutrients. Larger plants and plants that are growing robustly will need more water and nutrients, so linking nutrient supply to the water supply is a win/win situation all around.

Another advantage to supplying a continual low concentration of fertilizer is it eliminates the tendency of plants to show symptoms of nutrient deficiencies after they have received high doses of fertilizer and then been allowed to return to a more favorable level of soil solute concentrations. Even at perfectly acceptable concentrations of nutrients in the soil, plants previously exposed to high concentrations of fertilizer readily display these symptoms.

You will still need to guard against watering in sips and that habits accompanying tendency to allow solute (salt) accumulation in soils. Remember that as salts accumulate, both water and nutrient uptake is made more difficult and finally impaired or made impossible in severe cases. Your soils should always allow you to water so that at least 10-15% of the total volume of water applied passes through the soil and out the drain hole to be discarded. This flushes the soil and carries accumulating solutes out the drain hole.

I have recently switched to a liquid fertilizer with micronutrients in a 12:4:8 NPK ratio. Note how close this fit’s the average ratio of NPK content in plant tissues, noted above (10:1.5:7). If the P looks a little high at 4, consider that in container soils, P begins to be more tightly held as pH goes from 6.5 to below 6.0, which is on the high side of most container soil’s pH, so the manufacturer probably gave this some careful consideration.

To answer the inevitable questions about specialty fertilizers and "special" plant nutritional requirements, let me repeat that plants need nutrients in roughly the same ratio. Ratio is an entirely a separate consideration from dosage. You’ll need to adjust the dosage to fit the plant and perhaps strike a happy medium in containers that have a diversity of material.

If nutrient availability is unbalanced, if plants are getting more than they need of certain nutrients, but less than they need of others, the nutrient they need the most will be the one that limits growth. Whatever nutrients are available in excess, will be absorbed by the plant to a certain degree, and in some cases, this may lead to toxicity or even symptoms of shortages of other nutrients as toxicity levels block a plant's ability to take up other nutrients. Too much nitrogen will lead to excessive foliage production and less flowering. Too much potassium or phosphorus will not lead to ill effect, but will show up as a deficiency of other nutrients as it blocks uptake.

What about the "Bloom Booster" fertilizers you might ask? To induce more prolific flowering, a reduced N supply will have more and better effect than the high P bloom formulas. When N is reduced, it slows vegetative growth without reducing photosynthesis. Since vegetative growth is limited by a lack of N, and the photosynthetic machinery continues to turn out food, it leaves an expendable surplus for the plant to spend on flowers and fruit.

The fact that different species of plants grow in different types of soil where they are naturally found, does not mean that one needs more of a certain nutrient than the other. It just means that the plants have developed strategies to adapt to certain conditions, like excesses and deficiencies of particular nutrients..

Plants that "love" acid soils, e.g., have simply developed strategies to cope with those soils. Their calcium needs are still the same as any other plant and no different from the nutrient requirements of plants that thrive in alkaline soils. The problem for acid-loving plants is that they are unable to adequately limit their calcium uptake, and will absorb too much of it when available, resulting in cellular pH-values that are too high. Some acid-loving plants also have difficulties absorbing Fe, Mn, Cu, or Zn, which is more tightly held in alkaline soils, another reason why they thrive in low pH (acid) soils.

The point I’m trying to make in the last three or four paragraphs is simply that nearly all the variables in a fertilizer regimen pertain to the plants ability to handle nutrients, not to the actual nutrient needs of the plant.

So, If you select a fertilizer that is close in ratio to the concentration of major elements in plant tissues, you’re going to be in pretty good shape. Whether the fertilizer is furnished in chemical or organic form matters not a whit to the plant. Ions are ions, but there is one consideration. Chemical fertilizers are available for immediate uptake while organic fertilizers must be acted on by passing through the gut of micro-organisms to break them down into usable elemental form. Since microorganism populations are affected by cultural conditions like moisture/air levels in the soil, soil pH, fertility levels, temperature, etc., they tend to follow a boom/bust cycle in container culture, which has an impact on the reliability and timing of delivery of nutrients supplied in organic form.

What am I using? I start with a quart of 12-4-8 liquid Miracle-Gro all purpose plant food. To that, I add 3 Tbsp. of Epsom salts, 2 Tbsp. STEM (Soluble Trace Element Mix), and 1 Tbsp Sprint 138 Fe chelate and agitate until the concentrate is dissolved. I then try to fertilize my plants weakly (pun intended) with a half recommended dose of the concentrate and a little added 5-1-1 fish emulsion. The fish emulsion is for no particular reason except that I have lots of it on hand. This year my display containers performed better than they ever have in years past & they were still all looking amazingly attractive this third week of Oct when I finally decided to dismantle them because of imminent cold weather. I attribute results primarily to a good soil and a healthy nutrient supplementation program.

What would I recommend to someone who asked, for nearly all container plantings? If you can find it, a 12-4-8 liquid blend that contains all the minor elements would a great find and easy to use, but I don‘t think it‘s available. What I’m using does not have all the minors but I supply them with the STEM. You’ll likely find a 24-8-16 product readily available in granular, soluble form with all the minors, which is the same ratio as 12-4-8, so if I had to pick one fertilizer for use on all my plants, it would be that.

The chart I promised:

I gave Nitrogen, because it's the largest nutrient component, the value of 100. Other nutrients are listed as a weight percentage of N.
N 100
P 13-19
K 45-80
S 6-9
Mg 5-15
Ca 5-15
Fe 0.7
Mn 0.4
B(oron) 0.2
Zn 0.06
Cu 0.03
Cl 0.03
M(olybden) 0.003

If you're still awake - thanks for reading. It makes me feel like the effort was worth it. ;o) Let me know what you think - please.

Al Fassezke

Thumbnail by tapla
(Judith) Denver, CO(Zone 5b)

Great recipe, Al, and thanks for putting it together for us. I'm going to try to find all the ingredients you mentioned to use on my container plants next year and keep it on hand. I do have to water daily in our dry climate, so it'll fit just fine into my routine. Between what I've learned from you over the years and what I've learned from Ron on the morning glory forum, I should have the best morning glories around! :-)

Bay City, MI(Zone 6a)

Thanks for the very kind words, R. I get a little thrill every time someone indicates something I might have said or done for them has been helpful. For me, that's all the 'bang' I need to keep me hanging around here. ;o)

BUT - I mentioned a few things that I use that you'll likely have considerable difficulty getting. I'm going to paste a paragraph from above and ask you to read it again - please? I don't want to leave you or anyone with the idea that this is all that complicated or difficult, and the fertilizer I mentioned is a great choice. I have many friends hooked on it now, and it's been around forever, except perhaps for the fact that it now has the minors (micronutrients added), where it didn't have them in years past.

"What would I recommend to someone who asked what to use, for nearly all container plantings? If you can find it, a 12-4-8 liquid blend that contains all the minor elements would a great find and easiest to use, but I don‘t think it‘s available. What I’m using does not have all the minors but I supply them with the STEM. You’ll likely find a 24-8-16 product readily available in granular, soluble form with all the minors, which is the same ratio as 12-4-8, so if I had to pick one fertilizer for use on all my plants, it would be that."


(Judith) Denver, CO(Zone 5b)

I saw that part. If you think the recipe ingredients are too difficult to find, then I'll probably use the granular formula. But the liquid appeals to me. Takes less space to store. I have limited storage space for my gardening supplies.

Oakland, OR(Zone 8a)

Good evening Al. Thanks for the information on fertilizer. I enjoyed and am using the information on water in pots and watering. Now I'd like to take advantage of your knowledge of fertilizing - and I really like the idea of doing so each time the plant is watered.

Now for my problem. I have just checked the fertilizers I have on hand. I have five of them. If I give you a description of them, is there any way you could give me an idea of how to combine two or more of them to make approximately the ratio you think is the best? Or would it really be better to toss them and get new; keeping in mind a certain lack of funds. Oh, yes, and the main plants I have in container are those happiest in acid soils - i.e. Camellia's, Rhododendrons, Azaleas. The fertilizers I have on hand are as follows:
1. Expert Azalea, etc food 30-10-10 Granulated
2. Tomatoe Plant food 18-18-21 Granulated
3. OutdoorIndoor plant food 18-6-12 Pellated (8 mo)
4. Expert Bloom Plus 5-30-5 Liquid
5. Expert Rose Food 10-12-12 Liquid
I probably shouldn't bother you with this, but I really want to do the best for my babies-especially my Camellias.


Bay City, MI(Zone 6a)

Hi, Dotti. It looks like you went through some effort to check all your labels - and it's no trouble at all to try to help you - I enjoy being here with plant people. I just drove 105 miles (1 way) to a bonsai club meeting tonight to be with plant folk (and to learn a few things). ;o)

I'll show you how to figure your blend & then you can do it yourself. Fertilizer's NPK numbers are a % of the element in the blend by weight. 30-10-10 is 30% N and 10% each of P & K. If you mix equal portions of 2 fertilizers, you add the numbers together then average.

48-28-31 divided by 2 = a new blend of 24-14-15.5, which is fairly close to the same ratio as 3-2-2, and you're looking for a ratio of 3-1-2 (same as 12-4-8 or 24-8-16 - both very commonly available). There is really no way to combine what you have to come up with a ratio close to 3-1-2, except for your 18-6-12, which is exactly a 3-1-2 ratio.

I'm not saying that what you have won't work, it probably will be ok, but there will be luxury levels of some nutrients and deficiencies of others. I think you'll still be fine using the Miracid 30-10-10 (3-1-1 ratio) for your acid lovers, but you should watch for symptoms of K deficiency. Adding a little of the 18-18-21 tomato food each time you fertilize, which is high in K, or some potash, will help guard against that deficiency.

Lots of numbers to decipher there - I hope that didn't just confuse you. ;o)


This message was edited Oct 25, 2007 6:51 AM

This message was edited Nov 8, 2007 4:32 AM

Oakland, OR(Zone 8a)

Thank goodness I was a math major in high school, even if that was 50+ years ago. Yes, I understand what you were saying and I appreciate it. I suspect my plants will also. :-)

Fulton, MO

Great thread, Al!

It is very reassuring to see that my recipe mirrors that of the expert!

Do you back off on the fert in proportion to the water this time of year?


Bay City, MI(Zone 6a)

Hi, Robert. Thank you for the kind words. ;o)

You get a two part answer. I do suspend nutrition supplementation for the temperate plants I over-winter in a dormant or quiescent state, but no, I don't cut back on fertilizing with the normal weak solution for indoor plants in winter. I should explain something, though.

The reason we are told to cut back on fertilizer in the winter really isn't because plants don't use the volume of nutrients they do in the summer when they're growing well, we cut back to help guard against solute build-up in the soil, and the reason solute build-up is a problem is because it increases the electrical conductivity (EC) and makes it difficult for plants to take up water and the nutrients dissolved in it. While it's true that plants use less in the way of nutrients in winter, it surely does no harm to maintain the right mix of nutrients in the soil at a favorable EC range. It's kind of like heating your house with oil or propane. You may only use a few gallons every day, but it does no harm to keep an additional supply on hand for when it's needed.

This is another opportunity for me to plug a free draining, well aerated soil. It allows us to water freely, every time we water. This carries the residual fertilizer salts and carbonate build-up from irrigation water out the drain hole. Using a properly proportioned, weak fertilizer solution at every watering allows us to always keep the right nutrients available at optimum EC because we continually flush the soil. It hardly gets any better than that.

In winter, when most plants are growing slowly, and a grower uses a soil that does not drain well, they must water in 'sips' to guard against saturated soils and accompanying root rot. The low humidity of heated homes and often, placement of plants near heat ducts, increases evaporation rates and, in many cases, causes more water to evaporate than is used by plants. So, we're watering in sips, and watering often. Where do the residual salts go? They all accumulate in the soil and raise EC, making it ever more difficult for plants to stay hydrated.

This is probably the main reason, other than low light, so many people have such difficulty with low humidity and insects in winter (indoors). If the plant is growing under drought stress and cannot properly hydrate itself, the plant weakens due to a decrease in transpiration and photosynthesis. Slowed metabolism means less in the way of anti-feedants, anti-metabolites, alkaloids, and other bio-compounds that make insects unwelcome. It's easy to see the handicap we put ourselves under when we grow in an inappropriate soil.

I think I went beyond what you asked, but soils are very intricately related to a sound nutrient supplementation regimen and should be considered the foundation of every container planting. Besides, I offered the extra commentary for others who might not have your level of knowledge. ;o)


This message was edited Oct 28, 2007 11:41 AM

Oakland, OR(Zone 8a)

Thanks for the additional information. I learning information on things & processes I hadn't even begun to contemplate in the past. My poor plants. I have a big job ahead of me to correct all the mistakes. Well, it'll keep me busy. Dotti

Bay City, MI(Zone 6a)

Bob - if you're still around, I think I want to mention something else. I may have missed the meaning of your question, and what I said might be a little misleading. You asked, "Do you back off on the fert in proportion to the water this time of year?" I answered no, but that answer was based on the fact that I am already using a weak solution. If you were talking about temperate plants that overwinter outdoors or in cool conditions, and if you're using a full strength solution, there are two reasons to reduce the concentration that are not related to salt accumulation.

First - urea and organic based fertilizers at high concentrations in soils that are cold, and especially cold and waterlogged can cause dangerous levels of ammonia in plant tissues (ammonia toxicity). Low numbers of inactive bacteria that reduce ammonium to nitrate in these soils are the reason. Weak concentrations of nutrients in soils and well aerated soils help guard against this. So, if you are in the habit of dosing at full recommended concentrations, you should definitely reduce them to 1/4 to 1/8 recommended strength, even in fast draining soils, in winter.

The second reason is - plants growing in cold conditions simply cannot use the high concentrations of nutrients suggested on fertilizer container labels in winter, and most nutrients would be lost to leaching.

Dormant/quiescent deciduous plants will need no fertilizer - only water sufficient to keep the plant hydrated, until the onset of spring budswell.


Cincinnati (Anderson, OH(Zone 6a)

Another great thread, Tapla! Thanks for sharing all the detail of your research! t.

Cincinnati (Anderson, OH(Zone 6a)

Hi, tapla--

I was researching soils and planting mixes again, thinking of how I'm going to get my little seedlings under lights comfortably settled in their little garden and containers, and thought of this classic thread and your other excellent thread on container mixes and plant chemistry.

Now I'm wondering if you have had any thoughts on the 'tonic' known as 'Messenger', a harpin protein mixture used by growers and home gardeners for plant health and to boost production? (Here's a link explaining it for those who want some background: )

I wonder if it works and is worth the bother, especially to get all my flower seedlings off to a good start this spring. Any thoughts?

And likewise, I'm wondering if 'Superthrive', another 'tonic' with less scientific support but high retail sales, is useful for getting seedlings off to a good start.

Or maybe they are both the same thing, possibly?

So, tapla, would you happen to know anything about these or have an opinion?

Thanks so much. t.

Bay City, MI(Zone 6a)

I have practical experience using both of these products & have a whole case of 'Messenger' in my supply room. I've used 'Messenger' as a topical spray for about three years. Since the lion's share of my plants in containers are for bonsai, as I tend to them year after year, I get pretty intimately familiar with their growth habits and vitality levels. I also grow many garden display containers, some of which I try to duplicate year after year because of their superlative performance and appearance. I'm going to preface my observations about 'Messenger' by saying that I am usually very cautious and try to take a scientific approach to assigning a reason to what I observe in my growing efforts. In other words, I don't jump to conclusions.

Even though there were no controls in place for me to base my decision on, I believe I'm intimate enough with my plants that I can be comfortable with my considered decision that 'Messenger' is a good product. What I have noticed in particular, is that plants treated regularly with it seem sturdier and more vital. The leaves seem stronger and more vibrant in color. They also feel either thicker or stiffer. Plants seem to be more tolerant of summer's heat (high soil temperatures), and the individual blooms of flowering plants seems to remain attractive longer. I'll continue to use it.

My observations concerning the use of 'Superthrive' are based on something that at least had some loose controls in place. Here is a short article that I wrote a few years
ago regarding the product:

Superthrive or Superjive

The question regarding the value of Superthrive as a miracle tonic for plants is often bandied about in horticultural circles. Over the years, I had read claims that ranged from, “I put it on my plant, which had never bloomed, and it was in full bloom the next day.” to, “It was dead - I put Superthrive on it and the next day it was alive and beautiful, growing better than it ever had before.” I decided to find out for myself.

If you look for information on the net, you will probably only find the manufacturer’s claims and anecdotal observations, both so in want of anything that resembles a control. Though my experiments were far from purely scientific, I tried to keep some loose controls in place so that I could make a fair judgment of its value, based my own observations. Here is what I did, what I found, and the conclusions I made about any value the product Superthrive might hold for me.

On four separate occasions, I took multiple cuttings of plants in four different genera. In each case the group of cuttings were taken from the same individual plant to reduce genetic variance. The plant materials I used were: Ficus benjamina, (a tropical weeping fig) Luna apiculata (Peruvian myrtle), Chaenorrhinum minus (a dwarf snapdragon), and an unknown variety of Coleus. In each instance, I prepared cuttings from the same plant and inserted them in a very fast, sterile soil. The containers containing half of the cuttings were immersed/soaked in a Superthrive solution of approximately 1/2 tsp per gallon of water to the upper soil line. The other half of the cuttings were watered in with water only. In subsequent waterings, I would water the “Superthrive batch” of cuttings with a solution of 10 drops per gallon and the others with only water. The same fertilizer regimen was followed on both groups of cuttings. In all four instances, the cuttings that I used Superthrive on rooted and showed new growth first. For this reason, it follows that they would naturally exhibit better development, though I could see no difference in overall vitality, once rooted. I can also say that a slightly higher percentage of cuttings rooted that were treated with the Superthrive treatment at the outset. I suspect that is directly related to the effects of the auxin in Superthrive hastening initiation of root primordia before potential vascular connections were destroyed by rot causing organisms.

In particular, something I looked for because of my affinity for a compact form in plants was branch (stem) extension. (The writer is a bonsai practitioner.) Though the cuttings treated with Superthrive rooted sooner, they exhibited the same amount of branch extension. In other words, internode length was approximately equal and no difference in leaf size was noted.

As a second part to each of my “experiments”, I divided the group of cuttings that had not been treated with Superthrive into two groups. One of the groups remained on the water/fertilizer only program, while the other group was treated to an additional 10 drops of Superthrive in each gallon of fertilizer solution. Again, the fertilizer regimen was the same for both groups. By summer’s end, I could detect no difference in bio-mass or vitality between the two groups of plants.

Since I replicated the above experiment in four different trials, using four different plant materials, I am quite comfortable in drawing some conclusions as they apply to me and my growing habits or abilities. First, and based on my observations, I have concluded that Superthrive does hold value for me as a rooting aid, or stimulant if you prefer. I regularly soak the soil, usually overnight, of my newly root-pruned and often bare-rooted repots in a solution of 1/2 tsp Superthrive per gallon of water. Second, and also based on my observations, I no longer bother with its use at any time other than at repotting. No evidence was accumulated through the 4 trials to convince me that Superthrive was of any value as a “tonic” for plants with roots that were beyond the initiation or recovery stage.

Interestingly, the first ingredient listed as being beneficial to plants on the Superthrive label is vitamin B-1 (or thiamine). Growing plants are able to synthesize their own vitamin B-1 as do many of the fungi and bacteria having relationships with plant roots, so it's extremely doubtful that vitamin B-1 could be deficient in soils or that a growing plant could exhibit a vitamin B-1 deficiency.

Some will note that I used more of the product than suggested on the container. I wanted to see if any unwanted effects surfaced as well as trying to be sure there was ample opportunity for clear delineation between the groups. I suspect that if a more dilute solution was used, the difference between groups would have been even less clear.

It might be worth noting that since the product contains the growth regulator (hormone) auxin, its overuse can cause defoliation, at least in dicots. The broad-leaf weed killer Weed-B-Gone and the infamous “Agent Orange“, a defoliant that saw widespread use in Viet Nam, are little more than synthetic auxin.

Al Fassezke

Oakland, OR(Zone 8a)

Al, I'm not into trying to root cuttings, but I have started to try germinating seeds. How do you think Superthrive or Messenger would help me? Is there any assistance to be had or would I just be wasting my money? I have been fascinated by this thread and the two on water levels, and I certainly thank you for taking the time to answer our questions. Dotti

Bay City, MI(Zone 6a)

Oh - thank you for the kind words, Dotti. ;o) I think neither would be effective in germinating seeds. The effects of auxin (in Superthrive) on seed germination varies widely by species and cultural conditions, and I cant imagine what effect Messenger would have on germination. My opinion is that Messenger would be of benefit to seedlings after the first true leaves have formed, and from the experiments I described using Superthrive, I think it would probably be totally ineffective.

Remember - seeds have their own little store of nutrients & really don't need much in the way of help except for the right cultural conditions (the key) and perhaps a little helping hand from us in the way of some seed scarification in some cases.


Cincinnati (Anderson, OH(Zone 6a)

Oh, excellent posts, tapla. So informative and concise. I guess I hadn't relalized you did your 'experiments' with 'Superthrive'. Thank you for repeating all of it again here.

If you don't mind, I'll add this thread to my 'tags' list in my journal.

It appears that 'Messenger' is pretty highly regarded for harpin protein supplements.

And your last note on 'seeds having their own little store of nutrients' is very reassuring to me. I forget about that as I sit here on this snowy day obsessing about my seed starting set up and my seedlings!

Atlantic Beach, NY


We've been talking in the other thread but now I have a question.

If we are feeding when we water then what is the purpose adding the CRF and micronutrient powder in the formula ??

LASKA1 - Mike

Bay City, MI(Zone 6a)

This thread is about ongoing and o/a nutritional needs. The other thread suggests a CRF as an initial 'charge' in the soil. Its purpose is to provide at least some nutrition for the plants of the few who are either lax about supplemental nutrition or mistakenly believe container soils should, as part of their nature, hold ample nutrients in the right proportions to satisfy plant requirements w/o additional supplementation.

As long as you are diligent about regular fertilization, thus maintaining nutrient levels in the 'adequacy' range, there is no need for a CRF. I've mentioned that a number of times. ;o)


This message was edited Mar 21, 2008 10:35 PM

Atlantic Beach, NY


Sorry I must have missed that


Bay City, MI(Zone 6a)

You guys might find this information interesting:

Dr. Carl Whitcomb (PhD), makes 11 key points in the preface to his opening chapter on Nutrition in Plant Production in Containers II, which is pretty much a bible when it comes to growing in containers. Point 1 is in regard to the small soil volume, so we'll skip it.

2) "When other factors that can limit growth are not limiting, it is the combination and interaction of 12 nutrient elements that are responsible for energy production and growth in plants." This illustrates that how elements are combined, their ratio to each other, is essential to optimal growth.

3) "The more precisely the 12 essential nutrient elements are synchronized relative to plant needs, the more rapid growth occurs." Again, clearly stating that ratios are very important to most rapid growth.

4) "Excess of ANY nutrient, especially Nitrogen, is as undesirable as a deficiency." No explanation required

5) "When Temperature, growth medium, moisture, drainage, and oxygen to the roots and all other factors are optimum or at least reasonable, all, or nearly all plants grow best with the same proportions of nutrients. Plants grow at different rates, but the rate of uptake and utilization of the 12 essential nutrients is the same."

This hits pretty hard at the idea all these 'designer' fertilizers are required. You might say they're 'designed' to enhance the fertilizer producers' bottom line, rather than your growing experience.


Norridgewock, ME(Zone 5a)

I've been trying to keep my container plants fertilized as you suggest, and am encountering two problems. Wondered if you have any suggestions on either.
1) rain. If rain is occurring often enough that there is no need to water outdoor containers, what is one to do about fertilizer?
2) excess drainage. When the container is indoors, how, as a practical matter, do you manage the requisite excess flow from the bottom? Your post specifies quite a bit of water needs to come out. Many of my plants are too big to carry to the sink. If you have similar-sized plants, how to you manage that excess water coming out the bottom?
Thank you, as always, for your time.

Bay City, MI(Zone 6a)

1) If you're using the 5:1:1 mix or the gritty mix, there should be no problem applying a fertilizer solution as needed, even if the soil is wet. Keep in mind that plants use much less fertilizer during dull, humid weather than they do during dry days with bright sunshine. If you're using a heavy soil that retains too much water to risk fertigating when the soil is already wet and think nutrient levels are getting critically low, you can tip the pot at a 45* angle, which will remove a considerable amount of perched water. Inserting a wick into the/a drain hole will also drain additional water, which should allow you to fertigate with less in the way of negative consequences than if you had simply left the container in it's normal level position.

2) I grow on 4 x 8 sheets of FRP panel under lights. The panels have a hole in the center, and I designed the grow area with an intentional sag in the panel so all the water runs to the center & through the hole and is then channeled to a drain, so I don't worry about what to do about the excess water. In summer, all my pIants are outdoors on the decks or on grow benches. I don't know what to tell you, other than soluble salts do accumulate in the media and make it difficult for the plant to take up water & nutrients if you don't flush the soil regularly. It's best if you water copiously each time you water, but if you flush the soil thoroughly at least every two weeks, I don't think a salt build-up will be much of an issue.

PLEASE don't think I'm being snotty when I say that I can tell you 'why' it's best (or let's just say a good idea) to water, fertilize or do certain things in certain ways, but it's up to you to decide how far you're willing to go or how you're going to implement the methodology. The important message is the one letting you know that a high level of soluble salts in container soils is a major player in the decline of a high % of container plantings, and probably the single largest cause of the 'revolving door' plant syndrome. People often think their houseplants are only capable of living for a year or two before they have to be replaced, when in fact they are usually capable of outliving their owner with proper care.

If your heavy plants are in saucers, perhaps you could lift them up so their soil doesn't come in contact with the effluent after it drains. You could also suck it out of the saucer with a wet-vac or turkey baster, or just let it evaporate, in the winter. Maybe others have ideas, too.


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