How and when to fertilize blueberries

grovestead(4)May 30, 2014

We recently planted several blueberry shrubs in a fresh prepared bed of 50% peat and regular soil, and then mulched with pine needles.

Do we also need to fertilize with an acidic fertilizer? If so, how often?

I've read some places that coffee grounds can be used. Is that true?

Thanks!

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charina(6b)

Your first step should be to send a soil sample to your local extension service, or a soil testing lab and have an analysis done. Sure, you can throw some fert on there, but it is possible that nothing is needed except a nitrogen source. You can't adjust to where you should be unless you know where you are starting from.

Whether or not you need to fert with an acid forming fert also depends on where you pH is. Again, you can't get to where you want to be without knowing where you currently are. Your 1/2 / 1/2 mix may have brought you to a pH too low for using acidifying ferts if your soil was already favorable to bb's, or you could still be above 7 and the 50% peat didnâÂÂt even neutralize existing bicarbonates. A pH test can be done on the same sample you send in for nutrient analysis.

Frequency will vary according to the type of fertilizer you buy. You should follow the label directions on timing. Controlled release ferts will be once in the spring. Regular ferts will be smaller applications a couple times.

The one thing to keep in mind about timing is to cut off supplemental nitrogen at least a month before first frost, perhaps two if fall comes hard and fast in your location. You donâÂÂt want them growing aggressively still when the cold comes.

    Bookmark   May 30, 2014 at 4:05PM
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charina(6b)

If you are wanting to use the shotgun approach, here's what I would suggest: Use either Miracle Grow's all purpose continuous release plant food (shake 'n feed with the yellow cap) or Gertens acid loving plant fert. Apply one or the other early in the season after leaves are out. Both are controlled release and will fertilizer for an extended time. Were it me, I'd apply at 1/2 of the rate suggested on the label. BB's don't require a lot of fert (adapted to low fertility soils), and there is a good chance your soil has plenty of P & K already.

Then, on a weekly or bi-weekly basis, starting a few weeks later, disolve 1/8th or less of a teaspoon of Ammonium Sulfate per gallon of water, and water the root zone of the plant. That is about 1/2 the concentration rate I typically apply (I use just under 1/4 tsp per gallon), but that is to compensate for the nitrogen already in the controlled release ferts. Cut off the Ammonium Sulfate by the middle or end of July, earlier if you get frost in August. The application of Ammonium Sulfate will push rapid growth, and apply sulfur to continue to keep the pH down.

However, if your pH gets too low, you should stop the Ammonium Sulfate application, or switch to urea as your nitrogen source. Avoid nitrogen sources that are nitrate based. I didn't suggest Osmocote as a controlled release fert as approximately 1/2 of the nitrogen is nitrate based, rather than ammonical. People have used it without apparent deleterious effects, but there are better alternatives out there with less nitrates.

Water well periodically to ensure salts from a potential over-application of ferts have a chance to be flushed past the root zone.

This post was edited by charina on Fri, May 30, 14 at 16:38

    Bookmark   May 30, 2014 at 4:31PM
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grovestead(4)

Good information, thanks for all of this input. Regarding a soil sample, since BBs are shallow-rooted, should i send in a sample near the top of the soil or dig a few inches deeper?

What would be a sign if the soil is getting too acidic? It costs me $30 to get a soil sample, i don't want to keep doing paying that to know if my soil is at the right place..

    Bookmark   May 30, 2014 at 6:40PM
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charina(6b)

Honestly, unless you started with a naturally low pH native soil, it isn't likely you will get too low without trying hard. Pictures I have seen of bbs in to low of pH look a bit like fertilizer burn with browning leaf edges. And red pigmentation.

I don't think the standard soil sample instructions will indicate taking a sample deeper than blueberry roots will go. I think it would be fine just following instructions.

    Bookmark   May 30, 2014 at 11:08PM
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