How to apply these results to potted blueberries #723875 - Ask Extension


How to apply these results to potted blueberries #723875

Asked September 14, 2020, 3:57 PM EDT

I submitted a soil test back in early June, and for whatever reason only got the results today. The test results are code 36NWTM. Looking at the results, it says that next spring, I should apply .25lb of ammonium sulfate and .38 lb of TSP, but I want to make sure this is accurate, because the results above it say that every year, my plants need .1 lb of nitrogen / 100 sq ft. and .18 lb of phosphorous / 100 sq ft. The pots they're in are 20 gallon smart pots, which only have a surface area of about 2.2 square feet each. Do I need to adjust the amount to apply based on this fact? If so, by how much?

Wayne County Michigan

Expert Response

I am sorry you had to wait so long for an answer. I am the one who developed those recommends for blueberries for homeowners. Yes you should reduce that down for a pot I would suggest cutting them to a third. Our normal blueberry fertilizer recommendation is to apply half in the early spring and half after bloom when there is a lot of leaf growth.
This all assumes they are northern highbush blueberries. If you indoors are they evergreen? Southern highbush?
Another thought is you might consider using a rhododendron azalea complete fertilizer such as Mir-Acid for your potted blueberries
Mark Longstroth Replied October 02, 2020, 4:45 PM EDT
They are outdoors and planted in a mix of peat moss and pine bark mulch.  The reason for the pots is that my soil is high neutral and almost alkaline.  I have three different vacciniums: Legacy, Darrow, and North Blue.  I have been using Holly Tone up until now, but maybe I shouldn't be, given that the results are above optimum for potassium and magnesium.  So to follow the fertilizer recommendation, I would cut it by 1/3 of the per plant amount, and then halve that amount and apply the resulting amount in early spring and again after bloom?
The Question Asker Replied October 02, 2020, 4:52 PM EDT
Yes, cut the recommendation to a third. Then apply half (1/6) early and the rest after bloom. I am worried about burning the roots with too much fertilizer in the small pot. The leaves will draw the fertilizer quickly to the plant. You should get about 12 inches of new growth each season most of it in the spring and a second flush in late summer.
Mark Longstroth Replied October 02, 2020, 5:20 PM EDT

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