Fixing Raised Bed Soil for Dahlia Growing, Longmont 5b - Ask Extension
Hello! I recently got my soil test results back and it indicates that my nitrogen in my raised beds is low, but my phosphorus and potassium are very ...
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Fixing Raised Bed Soil for Dahlia Growing, Longmont 5b #865614
Asked April 23, 2024, 2:45 PM EDT
Hello! I recently got my soil test results back and it indicates that my nitrogen in my raised beds is low, but my phosphorus and potassium are very high. Actually, for "hand raising" this soil and using the hugelkultur method to fill these beds about three years ago, I am really surprised and quite disappointed in the results! I will attach a picture of the results for your reference, but I'm curious...how can I fix this? The testing company is recommending a 12-0-0, like blood or feather meal. But, I've also read that dahlias don't like a lot of nitrogen so I'm worried that this will tip the scales too far the other direction. I'm also really hoping that this is something that can be quickly remedied by adding things to the soil versus growing a legume cover crop because...well, I was VERY eager to start flower gardening this year and I'm about to have 30 dahlia tubers that need a bed (I KNOW I can't be the only one guilty of this) . I appreciate any guidance you can offer!
Boulder County Colorado
Expert Response
Hi Shawnee,
You sound well versed in gardening. That is an interesting soil report. There is no "fix" for soils, as it is a slow process to amend soil to change the composition slowly over time. Testing annually is a great idea so good for you to do that.
Nitrogen is the nutrient that is used up with plant growth, so not unusual for that level to be low in a well- used bed. Using a lower nitrogen level fertilizer like 5-10-10 is suggested for dahlias. However, you really need more nitrogen added than just a preset fertilizer can provide, so the blood meal suggestion for a growing season is a good idea. Aged cow manure worked into the soil - not straight compost - is a good alternative to a commercial fertilizer.
Penn State Extension has a nice information sheet on dahlias which I've linked here: The Dirt on Dahlias (psu.edu)
The soil report you provided shows high sodium, and one of the best ways to begin to lower that in soil is heavy watering (leaching) of the bed a few times before planting. Dahlias like a lot of water so remember this summer that with a higher sodium level they will need a lot of water. Caution to not let their "feet sit in water"
Planning for next year, you could try the cover crop (green manure) method to incorporate a nitrogen fixing plant (winter rye) into the soil.
You sound well versed in gardening. That is an interesting soil report. There is no "fix" for soils, as it is a slow process to amend soil to change the composition slowly over time. Testing annually is a great idea so good for you to do that.
Nitrogen is the nutrient that is used up with plant growth, so not unusual for that level to be low in a well- used bed. Using a lower nitrogen level fertilizer like 5-10-10 is suggested for dahlias. However, you really need more nitrogen added than just a preset fertilizer can provide, so the blood meal suggestion for a growing season is a good idea. Aged cow manure worked into the soil - not straight compost - is a good alternative to a commercial fertilizer.
Penn State Extension has a nice information sheet on dahlias which I've linked here: The Dirt on Dahlias (psu.edu)
The soil report you provided shows high sodium, and one of the best ways to begin to lower that in soil is heavy watering (leaching) of the bed a few times before planting. Dahlias like a lot of water so remember this summer that with a higher sodium level they will need a lot of water. Caution to not let their "feet sit in water"
Planning for next year, you could try the cover crop (green manure) method to incorporate a nitrogen fixing plant (winter rye) into the soil.
