Fertilizer for dahlias
I found this recommendation from the Maryland ext.
https://extension.umd.edu/sites/extension.umd.edu/files/2021-02/Nutrient%20Mngt%20Cut%20flowers.pdf
1.5-2 pounds per 1000 sq/ft.
My well water contains 20ppm nitrate nitrogen which is the value that I try to keep my fish tank water under. Jacks fertilizer recommends 50-200 ppm nitrogen every 1-2 weeks. I can't do the math so I just compare the color of our dahlia leaves to the trees in the woods. If the dahlia leaves are darker no fertilizer is needed. If lighter (never happens) I'd give them a boost.
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https://meridian.allenpress.com/jeh/article/42/1/14/499409
Nobody found the scholarly article. Note they recommend 150 pounds of nitrogen per acre. Bessie will gladly translate that to nitrogen per 1,000 square feet AND then recommend how much Urea (46%) that would be per 1,000 square feet and if you use a product that is 16% nitrogen how much of that per 1,000 square feet.
In my mind , I have guesstimated and decided that I have been using about this much but with Bessie's mathematical skills, she will verify that proposition.
On one of my plots (1/20th of an acre in size) I inject about 15 lbs of actual nitrogen in a 5 month growing period. That works out to about 225 lbs of N per acre. Considering my longer growing season, that is close to their recommendation. I think.
I knew that Steve would be one of the first to read the scholarly article.
I used my meager spreadsheet skills to determine how much nitrogen. My guess was about right but since I have poor records and apply "by feel" I could be off.
Takeaway: The people who say dahlias need low nitrogen fertilizer are mistaken. That is a polite word for just plain wrong.
"A recommended nitrogen application rate for potatoes is typically between 200 and 250 pounds per acre." So dahlias can be fertilized the same as potatoes as far as nitrogen although a bit less at 150 pounds per acre is good for dahlias and 200 is ok too but the 250 may be a bit much.
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Another quote form the paper:
"....the consequences of both reliance on and overapplication of compost-based amendments, particularly when applied based on intuition over soil test reports. Most growers indicated annual use of composts or manures, which are associated with elevated soil test P and K,...."
One can tell that the authors are from a farmer background where you must rely on soil tests to assist you to determine proper fertilizer for your crop. The quote intimates that many flower growers do not have a "farmer" background and they assume that products like compost and manure fertilizer are "good for flowers" and do not do soil tests. The phosphates in manure and sometime compost are a negative issue and the flower farmers applied too much.
Teddahlia just glanced at the article.
For those of us that don't deal with acres of plantings... Short answer:
If you have 10% nitrogen fertilizer you'd want to apply 3 - 4 teaspoons of fertilizer per square foot
150 pounds of nitrogen per acre is .055 ounces per square foot (thank you Google). If I use a fertilizer that's 20% nitrogen, then .055 ounces x 5 = .275 ounces of 20% N fertilizer per square foot.
If there's approximately(neglect specific gravity) 2 tablespoons (6 teaspoons) of the fertilizer in an ounce, and I only want .275 ounces, then I'd round up to use a little over 1/4 ounce of fertilizer (1.5 teaspoons) and apply about 2 teaspoons of the 20% fertilizer per square foot.
If you have 10% nitrogen fertilizer you'd want to apply 3 - 4 teaspoons, if you stick with the recommendation. I've got sandy loam soil, and because it doesn't hold nitrogen well, I would up any recommendation.
Why do I bother with these calculations? It's really good practice for my aging brain!
I do fertilizer applications 4 to 5 times per season. Small plants get small amounts . Bigger plants get more. Full grown plants very little.
Teddahlia , I agree that multi-dose applications I think are needed depending on the soil type.
This morning I felt like doing some research, so I took to Google with "research articles on growing healthy potatoes". I found what I think is a very thought provoking article on growing potatoes, but most more importantly, most of it I think will apply to Dahlias.
Potato nutrient management research: 5 things we’ve learned
October 25, 2023
In case anyone doesn't want to read the entire article, below are my notes( Excerpts from the article). But I highly recommend reading the entire article as it covers not just basics, but details some of the chemistry of how fertilizers move through the soil.
In Minnesota, potatoes are typically grown under irrigated conditions on sandy, low organic matter soils. Because of a high nutrient requirement and a relatively shallow root system (most roots are within the top foot), the crop is often responsive to applied nutrients, particularly the three primary macronutrients (nitrogen, phosphorus, and potassium).
1. Of all the essential nutrients, nitrogen (N) is the one most often limiting for potato production.
The fastest rate of N uptake occurs between tuber initiation and initial tuber bulking. Depending on cultivar, this can occur between 20-30 days after emergence.
2. Soil-borne diseases such as Verticillium wilt and root knot nematodes can limit potato root health and the ability to take up nutrients.
At the recommended N rate of 240 lbs N/acre for Russet Burbank, N uptake in fumigated plots increase by 50 lbs N/acre over non-fumigated plots…
3. Improving soil health in potato cropping systems is difficult and takes time but there are some promising strategies that may help.
Soil health is a challenge with potatoes because of the significant soil disturbance that occurs at planting, hilling, and harvest, as well as the need for fumigation to control soil-borne diseases.
4. Phosphorus (P) is a macronutrient that is essential for all forms of life. A deficiency of P in potatoes is associated with delayed vegetative growth, poor tuber set and bulking, and reduced yields. Excess P seldom affects plant growth…
…For this reason, some P fertilizer is usually recommended for potatoes even when soil test P is high. However, a P response is not always guaranteed, even on lower P testing soils.
5. Not enough (and too much) potassium can impact potato yield and quality.
Potassium (K) is an essential element required in high amounts for profitable potato production. High tuber yields can typically remove over 250 lbs K2O/acre.
The most common K source is potassium chloride (0-0-60). Chloride is also an essential element. It is considered a micronutrient but is taken up by the plant in macronutrient quantities.
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Bessie Excess P seldom affects plant growth…
I think part of the reason this is true for potatoes and not dahlias is alluded to in the article:
- Potatoes are grown at pH 5.5 to discourage scab (or was it rust). Soil this acid would create a need for more phosphorus.
- The mechanical process of "hilling" destroys many feeder roots and creates a need for more P.
5.5 pH is the upper limit for good potatoes, they like much more acid than 5.5.and about 5.0 would be lots better. Dahlias like pH in the sixes and 6.2 to 6.5 is what they like the best.