How Much Nitrogen?

13 years ago

Dahlias are heavy feeders and need lots of nitrogen. There are people who say that they should not get a lot of nitrogen and they are wrong in most situations. Mac Boyer, a member of a the American Dahlia Society and the director of a dahlia trial garden uses urea to fertilize the trial garden entries. Urea is the 46% nitrogen and is also very inexpensive. The plants in the trial garden do very well.

If you are a serious gardener, you will get a soil test done to determine what fertilizers and soil supplements you should be using. Phosphorus can build up in soil to plant toxic levels. If you are always using a fertilizer with a high phosphorus numbers, you may actually be poisoning your dahlias.

If you are a commercial grower and your product is dahlia tubers, you will probably use less nitrogen in your fields. Dahlias fed with the proper amounts of phosphorus and potassium(especially potassium)and somewhat low levels of nitrogen produce more tubers and the tubers store well. You would also be concerned about having the plants grow too tall and fall over. The home gardener ties up his dahlias to stakes and is more concerned about flower production than tuber production. Dahlias reach their best potential when fertilized properly and that includes nitrogen in the mix.

The home gardener should not fertilize the dahlias for at least a month before he digs and divides them. The excess nitrogen causes the plants to produce immature tubers that do not store as well.

Comments (4)

pdshop
13 years ago
I am very conscious of the chemicals I use. I read everything and no one agrees. It is so confusing when that happens.
I did the soil test last Spring. It said 7. I did my kelp feeding and wood ashes through the winter, old grass, (ii is supposed to be chemical free), and just put a little bonemeall in with the tubers. I don't know if that is right our wrong. The year was so strange anyway. I had short dahlias, ones that didn't open, yellow leaves, and some that were 5ft high? I don't know!
teddahlia
Original Author
13 years ago

"I did the soil test last Spring. It said 7."

Apparently you did only a ph test. Dahlias do not grow well at this ph. Ideal ph from my experience is 6.1 to about 6.6. If you add wood ashes to the soil you are making the problem worse as wood ashes are alkaline. You need to have a more comprehensive test done that includes trace elements. The testing company will give you a recipe to improve your soil in both an organic or inorganic way.

I have noticed too that many organic gardeners tend to put too much organic material into their garden just before planting time. If the material has not fully decomposed, the bacteria in the organic material competes with the dahlias for nutrients. Organic material should be added in the Fall if possible. Also, grass or hay products quite often contain herbicide residues that are toxic(dahlias are really sensitive).
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pdshop
13 years ago
What do you suggest for N.? I didn't add the wood ash this year. The ground froze beforre I could do much of anything but get the tubers out. Lord they are big. Ccan you imagine if you got a big bush from just one tuber and yours puts out 20 and they all have eyes? We could cover the state. How many eyes has anyone found on a big clump of tubers before?
teddahlia
Original Author
13 years ago
If you are organic there are expensive and less expensive sources of nitrogen. The more expensive are bat guano and blood meal and fish pellets. All are available here in the Portland Oregon area but I bet not very available where you live.

Probably the best and cheapest source of nitrogen is alfalfa pellets or hay. Pellets are a bit easier to handle as they come in bags and can be spread quite easily. Hay is cheaper but comes in big heavy bales.

Alfalfa not only has nitrogen but also some phosphorus and potassium. The best news is that it has a plant stimulant in it that makes dahlias and roses grow better. Rose people have been singing it's praises for several years now. If you spread some on the soil in the early Spring, it will decompose enough to give plants a real boost.