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How to Fertilize cell packs? & How/when to harden off?

Sun City, CA(Zone 8b)

Hi All and Thanks,

Sorry if this has been posted before- I've been looking for an hour and haven't been able to find the answer.

A quick history: I have tried planting seeds twice before with almost 100% germination and cute little seedlings that have never made it once they were outside. I am growing about 1000 plants (mostly perennial, but some annuals) in jiffy pellets and some in egg crates with jiffy starter mix inside my house. I have experienced damping off with my penstamon and am using a fungicide now on those, but no other visible problems. (Well, except for the cat seeming to mistake the Sleeping Beauty Commelina with catnip...)


1. When do I start fertilizing my seedlings and how do I go about it? Please any suggestions :)

2. When and how do I get them outdoors without killing them? I have only found step-by-step guides for tomatoes. Do I have to transplant to individual pots before putting them in my garden? I hope not, because I have nowhere to put 1000 pots! :)

Thank you so much for any help you can offer!!

Canyon Lake, TX(Zone 8b)

I used jiffy pellets for several years and to become successful I had to learn to water from the bottom and not over water. For me damping off seemed to be caused by over watering.

This year I used . I had good success with this setup and found it easier than Jiffy pellets to get seedlings to the potting up stage. In the future I will fore go using Jiffy pellets.

My biggest challenge is to keep plants from getting leggy. I use a heat mat to achieve quick germination. Once the seeds germinate I try to keep the room temp at around 50 - 60 degrees and the grow lights at 1/2 - 1 inch above the seedlings. Remember the grow lights give off some heat. From the get-go I water with a water soluble fertilizer mixed at the rate of 1/4 tsp to a gallon of water.

I like to pot up when the second set of true leaves have just appeared but are still small. I only pot up once before I plant out into the garden. I plant out early and cover when temps are forecast below 45 degrees.

This weeks has been perfect for hardening off seedlings. Our temps have been around 75/55 with light to moderate wind, fairly high humidity, overcast skies most of the day and sunshine a couple hour late in the afternoon when the sun is low in the sky....just perfect.

Casper, WY(Zone 4a)

I agree with all that texasrockgarden wrote, except I don't like jiffy pellets since they dry out too quick.

Once the true leaves appear, begin feeding with Miracle-Gro at 1/4th dilution from the direction.

If your plants are growing and are healthy, the problem may be that you have to harden them off before planting in the ground. Place the jiffy pellets in a flat close together to prevent them drying, or enclose each or several in plastic. Place them on the east side of a building so they get morning sun only. Keep them like that for a week and gradually move them to more sun. They not only have to get used to sunlight, but also fresh air which can be drying with movement of air on leaves.

I have always saved plastic containers to use over plants when planted in the yard. Milk gallons are great when threaded over a towel to prevent it from blowing away. Pop bottles will work too. Cut an opening on one side and face the opening towards the sun. It will keep the hot rays off the plant while it becomes established in the garden, yet it will receive sun.

You can follow the general directions for tomatoes and apply it to any plant. The mistake new gardeners do is not hardening off plants before planting in the garden AND not giving some protection after. The leaves grown in the house is not as tough as those grown when outdoors and exposed to the elements.

Google information you want and I'm sure it is out there. Good luck and enjoy!

Sun City, CA(Zone 8b)

Thank you so much for your help. I think texas may have a good point that I may be having problems in part due to my lights being almost 2 feet above the seedlings since they are on the kitchen counter. I didn't see a problem with them being "leggy," but that could be contributing to disease. I will try putting them on boxes so they are closer to the lights :)

I have stopped overwatering, but seem to be having a problem with the Jiffy in keeping them from being either too wet or too dry. I will take your suggestions and avoid those in future.

Thanks blomma- I wil start feeding the miracle grow to my little ones that have their true leaves sprouting. I didn't know how many they needed before the Miracle Grow would be too much.

I may also have it too warm-- we keep the house heated between 71-74... I wonder if I'm cooking my plants?

I've noticed I'm losing some as their roots start exteding out of the jiffy pellet. I'm going to try potting those and see if it helps. Their growth seems to have stopped :(

Thanks for the help!

Galesburg, IL

One other observation on temperature and light. Higher temperatures and lower light intensity equal very tender and leggy plants. I try to keep everything I am growing under lights no warmer than 65 degrees to help reduce leggy growth. You may not be able to keep your plants this cool, but one thing you can do to help strengthen your plants is to provide some air movement. This helps build cell wall thickness in plant stems and will result in much sturdier plants when you move them outside. I don't mean turning on a fan blowing directly on them, but rather a fan placed so that there is a gentle breeze that occasionally causes leaf movement. If you happen to have a ceiling fan in the room with your plants, this is ideal. If you don't have a way to add air movement, just brush your hand across the top of the plants several times a day, or each time you walk past them.

Sun City, CA(Zone 8b)

Thank you! I did not know that. Since I live in southern california and tonight should be my last night of frost, I am going to start putting them outside today so they can adjust (and probably benefit from) the cooler temperatures outside. I do have a ceiling fan, but since it is winter it has rarely been on. I was brushing my hand across them in the beginning until I started to notice the damping off... I've tried hydrogen peroxide and a fungicide and neither seem to help that problem. I've been letting my plants get too dry to try to get rid off the fungus problem and losing some of them to dryness.
But, I still have quite a few survivors :) I told my husband even if we only have 6 plants survive (I still have about 500) we still came out even on cost! :)

St. Louis County, MO(Zone 5a)

I use jiffy pellets very successfully. You are correct, once the little white roots start hitting the air, the growth stops. It is time to pot up.

Galesburg, IL

Just to expand a little bit on Cathy4's comments. When the root hits the air, that part of the root that is exposed stops growing, but what happens is that root starts sending out many more root fibers on the interior of the soil media. The process is comparable to what happens when you pinch back the growing point of the foliage, you get a much bushier plant. Commercially, many perennials are grown in plant bands or plant tubes that have no bottom. when the roots hit the air, many more fine roots are established. For certain perennials (those with tap roots), this is very advantageous as it produces much more root mass to help support the plant when it is transplanted. Note however, that the tubes used are usually around 6 inches tall, not the one or two inches in the pellets. With the taller containers there is much more room for root mass to be established. With the pellets, I agree that it is time to transplant to larger containers.

I start all perennials mass sowed in 4 inch pots and then transplant to 2.5in square pots that are 3.5 inches tall. They will stay in those pots until they are transplanted to their final location, no matter how root bound they become. Becoming root bound, while not ideal, is not that bad a thing to occur as long as you have a pot with minimum dimensions. In my case, the 2.5 inch pot has proven to be ideal, even if I have to leave the plant in them for up to six months. Space, money and time are also considered. Would I step up all my perennials into 6 or even 8 inch pots if I had the time and space? Maybe, but probably not. The difference in plant growth over the course of a season comparing plants from different pot sizes (assuming the same plant age) would be negligible, and no mater how large a pot you use, most perennials won't bloom until at least the second year anyway. In addition, the 2.5 inch pots only cost pennies apiece and can be used year after year with just a little cleaning and sanitation. FYI, I grow about 750 perennials each year using this method (I would never have the time or space if I used larger pots).

(Pam) Warren, CT(Zone 5b)

Where do you get the 2.5" pots? Gh megastore sells in lots of 800! But I like the sound of your system. I'm in NYC for the winter. It's impossible to find decent supplies here! Home depot has jiffy and a little Burpee, mostly pellets and peat pots which I hate- they fall apart so you can't move them around once they're wet, but in the ground you find little hard slabs months later. Ick! I've been all over the city looking for 4" pots and no one has them. Am I the only city gardener? Or everyone else knows to bring the right things from the country.

(Pam) Warren, CT(Zone 5b)

I ended up using 7 oz Dixie cups. Better than nothing I guess...

Galesburg, IL

You didn't look far enough on GH Megastore. Like all trays and inserts they sell them in "hobby pack" sizes. 32 - 2.5 inch pots for $2.00. Here is the direct link to the 2.5 inch pots.

You can't beat the prices at $0.0625 per pot. Another great thing, they fit exactly 32 per 1020 tray.

St. Louis County, MO(Zone 5a)

Thanks TRC, that is interesting information. I forgot to mention that I order the larger size pellets, so I do have a longer time before potting up and I pull open the tops when I plant seeds in them. Dixie cups work fine, I use them, too, and tall cups for tomatoes so I can plant them deep.

(Pam) Warren, CT(Zone 5b)

Thanks trc! I started the tomatoes in mini greenhouses that come with coir pellets, found in Home Depot. In no time the roots were coming through the bottom - when the pellets expand they are only 1" deep- so I had to pot them up. 2.5" pots would have been perfect. I need to keep them small here because of space. Next month when we open the house I'll put them in big enough pots to bury the whole stem again and put them in a cold frame to grow on and toughen up. Can't wait!

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