Dahlia fertilizer

Everson, WA(Zone 8a)

What do you use to fertilize your dahlias? I keep reading that it has to be really low in nitrogen but I have never seen a fertilizer like that. I use compost and sometimes bone meal but I wonder if there is anything else I should add.

Everson, WA(Zone 8a)

Candy I use nothing. Haven't ever since a guy who sells them and shows them told me it was actualy bad for them especially the nitrogen which applied to late in the season causes the tubers to spoil in storage. When are you coming. Ernie

Thumbnail by eweed
Willamette Valley, OR(Zone 8a)

Awe, what a great photo, Ernie!


Everson, WA(Zone 8a)

What a sweet picture Ernie. Was that on your property?

You don't need to fertilize - I have seen your soil. All you need to do is toss stuff on the ground and jump back. LOL I guess I won't worry about fertilizing then. The compost and bone meal should be enough.

I am still planning on coming out in July. I haven't set a date yet. Can't leave until I get everything done here and I feel so far behind. It has finally warmed up enough to start putting things in the ground, like tomatoes. So hopefully this week I will accomplish a lot of planting and begin to see the light at the end of the tunnel.

Lincoln, NE(Zone 5b)

I planted my pots ones in MIracle Grow plus potting soil. Do you think this will have too much fertilizer for them? Someplace I read that 5-10-10 was a good fertilizer for them. See, I needed this forum before they were a foot tall!


Everson, WA(Zone 8a)

I have read that dahlia fertilizer should have low or no nitrogen. It causes the plant to make a lot of leaves at the expense of flowers and, as Ernie said, the tubers will rot in storage. I don't know if there is enough Miracle Grow in the mix to do any damage. Maybe an expert will come along to advise.

Aren't dahlias wonderful? :^)

Temecula, CA(Zone 8b)

We're no experts by any means, yet all we use is compost for N, our homemade compost tested out @ 1.5%N, which is basically just enough N to keep compost decomposition going after it's applied to the soil. We do add bone meal and greensand to keep P and K with some trace supplemented. This is only the second year for the 40 or so Dahlias we have. Our soil is deep and sandy so we left them in over the winter and they've all returned, even the bedding dahlias which I assumed were going to behave like annuals. That's what I get for assuming...lol.

We were also told by the Dahlia person we got our tubers from that high N was the eventual kiss of death for the tubers.

It's wonderful that this forum exists so all of us can share these amazing flowers.


Everson, WA(Zone 8a)

Candy the fawn was at Ernies. Try to visit this time before you leave lol maybe we can both be home that way ha ha. Ernie

Everson, WA(Zone 8a)

And maybe it won't be raining!

Stanford, CA(Zone 9b)

drdon - LOL The bonemeal would certainly be the kiss of death for my Dahlias. Not because of any chemical problem. My puppy digs up EVERYTHING planted with bonemeal. I just lost a rose bush to bonemeal. :-) But you have the magical ingredients to make everything grow.

One site suggests using the same type of fertilizer they do on potatoes.
It looks like your miracle grow shouldn't be a problem although he does recommend more nitrogen than I would expect.

I've been feeding my Dahlias the same thing I feed my Iris. 5-10-10. I'd use bonemeal too - but I've had the doggie problem.


They recommend cow manure but my guess is that they didn't have access to horses. :-)

I do think that any bulb or rhizome that is flowering needs a low nitrogen fertilizer as a general rule.

This message was edited Jun 6, 2005 11:14 AM

Stanford, CA(Zone 9b)

I think that we would do very well to make a sticky out of this thread. I've noticed in the Iris forum that we tend to have these questions over and over.

The other sticky we should have is pest control.

And maybe the third for planting and propagation.

Should we ask Terry and Dave?

Willamette Valley, OR(Zone 8a)

Sounds like a good idea to me.

Seattle, WA(Zone 8b)

Here's a great link for some good basic info.


Oklahoma City, OK(Zone 7a)

Dahlias grow best in a pH range of 6.0-7.5 and require good levels of phosphorous and potassium (potash) to flower well. If too much nitrogen is in the soil (or added to the soil), the plant will produce fantastic foliage, but not many flowers.

Mulching is good to preserve moisture. It doesn't have anything to do with the quality of the soil (get a soil test done if you want to know just what the level of nutrients is in your gardens).

Dahlia tubers should not be planted deeper than 4-6".

Riverview, NB(Zone 5b)

I planted my tubers in large box. 2 1/2 feet wide, 2 feet deep, and 8 feet long. I filled the box with, Horse Compost Manure with a little Bone Meal thrown in each hole.

I hope this isn't going to be too much. I'd like the tubers to multiply if I can get them to do that and dig them all up in the fall for next year.

I've never grown Dahlia's before and to be honest, I don't know why. Maybe I always felt they were a little too expensive for me to buy, I don't know. Anyway, I've always liked them, and someone here at DG gave me 6 of them. The day they arrived, I had them planted. :)

Stanford, CA(Zone 9b)

It will be very interesting to see what happens. Be sure to let us know! You'll love your dahlias.

Monroe, NC(Zone 7b)

I asked this nutrition question of John Kreiner who is the president of the GA Dahlia Society. He told me that there is a product developed at Clemson University called Maxesea which is 3-20-20 with seaweed. Charlie's Greenhouse sells it. That sounds like a good nutrient ratio for dahlias. I have been using Peters 20-20-20 (sort of like Miracle Grow). My plants are sort of big. But they also seem to have plenty of flowers. I do plan on changing my nutrition program though. I don't like having to stand on my tippy toes to disbud!

Riverview, NB(Zone 5b)

If you have one kind of fertilizer that is, 20 - 20 - 20 and another fertilizer that is 4 - 16 - 16, and you mix the two of them together, does it end up being, 24 - 36 - 36?

Monroe, NC(Zone 7b)

Wow...this is a brain teaser requiring a math genious. Here is how it works. 20-20-20 means that the fertilizer contains 20 pounds of each (N-P-K) per 100 pounds of fertilizer. So basically it is a percentage. The math question of the day is....How do you add percentages. Where is my 9th grade son when i need him??

Stanford, CA(Zone 9b)

If 100 pounds of one type of fertilizer has 20 pounds of N and the other has 4 pounds of N in 100 pounds. Then if you mix equally by weight you get 24 pounds of N per 200 pounds of fertilizer. So the answer is 12 pounds of N per 100 pounds of fertilizer. See, no percentages required at all!

However, there is no telling what form of nitrogen is in what fertilizer so I really don't know what you're getting if you mix them.

But then some kids just take horse poop and ground bones and throw them together. Who knows what the N is in that? (LOL)

I've seen dahlia sites who suggest 20-20-20 slow release and some who recommend a lower N fertilizer. Guess you just try and see.

Albany, OR(Zone 8a)

Dahlias don't like too much N. That is why a low N level of fert. is better. You don't want tons of foliage, you want the flowers!!!!

Riverview, NB(Zone 5b)

I always wondered how they came up with different variations of fertilizer. i.e., 20-20-20, 10-10-10, 4-10-10 etc. So I wondered if I might be able to make something up myself. (not just for Dahlia's) It was more or less a general question because I was in a "Fertilizer" forum.

It's a little more complicated than I thought. I'll stick to what I'm using for the Dahlia's, however.

I don't know what level of N Horse Manure has, but that's what my Dahlia's are planted in. Horse Manure Compost with a little Bone Meal in the hole.

Hagerstown, MD(Zone 6a)

This sounds like the same type recommended for irises. What other plants require low N?

Stanford, CA(Zone 9b)

Darrell, Sorry, I was just being silly. It was a great question and I didn't mean anything personal. I really am very interested in what your method brings. If you've hit other places in the Dahlia forum, you'll find that drdon is a great believer in horse manure for most everything. His Dahlias are early, beautiful, and healthy. Check out his threads here.

Iris and most other bulbs do best on bone meal or 5-10-10. Cooley's sells their own Iris fertilizer that is even lower in N.

Oklahoma City, OK(Zone 7a)

It isn't so much that they "require" low nitrogen ... but when the plant is provided with higher levels of nitrogen, more foliage is produced and fewer flowers. Any flowering or fruiting (veggies, too) plant falls into this category. Phosphate is what flowers and fruits need in order to bloom.

Riverview, NB(Zone 5b)

That's good to know, Smiln32.

I have to tell you, this whole business of fertilizer has me overwhelmed. I use to think that if you just planted your things and used a good manure, (cow or horse), that was all you needed to have a successful garden. Well, that an a bit of elbow greese. :)

Now I'm finding out that you have to have a certain PH, a certain amount of Nitrogen, a certain amount of this, that, and the other thing. I can't keep up with it. Then came the "Planting by the Moon" stuff and "Planting in Gemini" and "Not" planting in "Scorpio".

If I weren't a sound sleeper, this would "all" keep me awake at night just thinkin about it. LOLOLOL

Willamette Valley, OR(Zone 8a)

I'm right there with ya Darrell! I throw my plants in the ground and spray them with Miracle Grow once a week in the summer time. I have no idea about all this PH, nitrogen, phosphate, etc,etc,etc......LOL

Oklahoma City, OK(Zone 7a)

I learned a lot by taking Master Gardeners courses through our local Cooperative Extension Service. We have high pH values in many areas here where I live....also high saline (in the soil). It makes a big difference in how plants survive. Azaleas, for instance, need acidic soil. That's very hard to come by here in central OK - and you just can't change your soil overnight. What's more is that most of the water you'd use for your plants has the same pH as the soil, so that has to be taken into account, too.

Dahlias can handle higher pH values than azaleas. Many plants can handle a wide range of pH values, in fact, so for most folks (and most plants) it's not a problem.

Riverview, NB(Zone 5b)

Pot Ash.

Are the Ashes from the wood burner/fireplace the same as Pot Ash?

Could I use the ashes from the wood burning stove?

This message was edited Jun 29, 2005 6:43 PM

Oklahoma City, OK(Zone 7a)

Pot ash is not the same as wood ashes.

Wood ashes are high in calcium, but only contain small amounts of other nutrients. They provide essentially no nitrogen, 1-2 percent phosphate, 4-10 percent potassium and some micronutrients. Consequently, their use as a fertilizer is very minimal. Do not rely upon ashes as your fertilizer source. per (http://www.mobot.org/gardeninghelp/hortline/messages/3109.shtml)

Potash is "A potassium compound especially as used in agriculture. The third number in the NPK ratio" per Paulgrow in our own Garden Terms section (http://davesgarden.com/terms/go/694/)

Riverview, NB(Zone 5b)

I'm trying to come up with something that is low in Nitrogen and high in the last two. To make more flowers and less foilage.

I know I have that much right. Low Nitrogen and high Potasium? Pot Ash?

Oklahoma City, OK(Zone 7a)

You got it!

Stanford, CA(Zone 9b)

Does anyone know about Milorganite? They use it on Daylilies and the label says that you can use it on flowering plants - but it's high in N.

Oklahoma City, OK(Zone 7a)

I wouldn't use it on my flowering plants. It would be great for your lawn, though.

Issaquah, WA(Zone 7a)

Does anyone remember the movie "Goldfinger" from the 60's?

Well after reading Dr Don's post above I was out singing 'it's the kiss of death--- for Mr. Dahlia Tuber' all day while watering two beds. I am in denial and don't want to believe the nitrogen thing because 3 weeks ago I got sick of slow/ short dahlias and threw on my trusty old 19-14-10 or so Osmocote on ALL dahlias. I just didn't think the `10-10-10 I used at planting was doing the trick.

Oh woe is me. I hope I have enough season left that it will magically metabolize out and my tubers will not be pulp. I used this same Osmocote early last season and had great tuber storage, so I'm crossing my fingers that I didn't add it to late.

Here is a link to more than you'd ever want to know about manures

Stanford, CA(Zone 9b)

Arggh. Now I know why I had some Iris rot (sorry, wrong forum, I know). I used some organic amendments and they were very high in chicken manure. an 83 N rating. No wonder they rotted. Thanks for the link Poochella. I was right about the reason for rot.

Chico, CA

Soooooo.... chicken poo must be high in nitrogen.... I put plenty on my dahlias and veggie garden about half way through the summer and now I have lots n lots of foliage.... not many maters and not many flowers on my dahlias now....but lots of the green stuff.... live n learn...Dottie

Stanford, CA(Zone 9b)

At least we hope learn. :-)

Aptos, CA

I use all organic fertilizer and get fabulous blooms. After I dig I will plant a crimson clover cover crop, til that in Springtime, add an organic dry 16-16-16 along with humic acid pellets. Set the tubers and surround with worm compost. I foliar feed with a liquid organic like Dr. Earth, and also add compost tea through out the growing season. Its been a lot of tending, but worth it. There are lots of earthworms in the soil, happy bees and butterflies!

Albany, OR(Zone 8a)

How come we don't get to see your apparently beautiful dahlia pictures?
Would love to see yours!

You sure do a lot of work with getting the ground ready for the dahlias.
I think I will do something similar to what you have mentioned here.
Using crimson clover is a great cover crop for any type of bed, especially veg. gardens.
You have great ideas.

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