Why do you want to use ammonium sulfate instead of acidifying your irrigation water w/vinegar or citric acid?

Al

I regularly add vinegar to my watering (1-2 tbsp in a 2.5 gal watering can). But I've never known how to fertilize the blueberry plants and although they look healthy, they aren't growing as fast as I'd expect. Last year I tried adding soil sulfur and also fertilizing with something (probably miracle gro), and ended up with two dead blueberry plants. This year I'm trying to be more cautious about it. Ammonium Sulfate instructions just tell you to toss in a handful, but after my experience last year I'd like to be a bit more precise than that.

If you had problems with sulfur, then you'll have even more problems with ammonium sulfate.. it acts far faster. Sulfur has a lag time due to the need for microbial metabolism to sulfates and sulfuric acid; ammonium sulfate will be active as soon as its dissolved. This is why it's generally not recommended for use by home gardeners (in my experience) and definitely not to be used in containers.

MG fertilizer in a 3:1:2 ratio is a good choice, John. DO stay clear of fertilizers that get their N from nitrate sources - MG fits the bill as it's urea-based.

What are you growing them in (soil) and how did you fertilize? You don't need the aluminum sulfate, but it would probably be helpful to use the vinegar each time you water (adjust fresh tap water to a pH of about 4.5 - 5.0) and just fertilize with half strength doses of MG as required to keep foliage color nice.

Are the plants zone appropriate? Could they have over-heated?

Al

The blueberries are in 1/2 spagnum peat moss and 1/2 potting soil. I've been using half strength miracle gro when watering other plants in containers, but I'm still a bit shy about it with the blueberries because I always suspected it was the cause of my problems last year. It's good to know that it's ok to use at this strength. I think I figured out that 1/2 strength (1 tbsp in 2+ gals water) is about 200 ppm. Does that sound right for miracle gro? How about using the miracle gro for Azaleas, would that be better.

I don't know if the plants are zone appropriate, but they were all bought at local nurseries(Misty, Southmoon, O'Neil, Jubilee, Sharpblue, Emerald, Star,and some others). I get plenty of chill up here, and the summers can be hot, lots of 90-95F days. I try to wrap the containers with something to keep the sun off the black plastic. The blueberries also get some shade during the day. Ultimately I'll have them all in 15 gal containers, but right now only three are in these large ones.

The reason I was going to use the Ammonium Sulfate was that I read more than once that it worked well with blueberries, although I don't remember if the references were to in ground or container plants. I was interested in it as a good fertilizer that also was acidic. Is everyone saying not to even think about using it with blueberries?

Have you tested the pH and Total Alkalinity of your water? 2 Tablespoons of vinegar in 2.5 gal of water would drop the pH at least 5 points. I recently tested mine and 1/2 teaspoon dropped the pH of one gallon, one point. I plan on trying 2 blueberry plants in containers this year. 4 teaspoons of vinegar per 2 gallons of water would get my water down to a pH of 4.

One tbsp of vinegar in 2.5 gals of my water drops the pH to 5.5-6.5. I was trying 2 tbsp because I read that blueberries handled summer heat best at a pH of 4.5-5.5 so I reasoned that it would be worth trying the extra vinegar. I haven't tested it much so most of the time I stay with one tbsp. You must have much stronger vinegar that I do, I use the cheap stuff from the supermarket. When I've checked the water pH it's usually been right at 7.

The buffering capacity (the amount of acid or base it takes to change pH) of various water supplies varies widely, so the amount of vinegar it takes to change the pH of Jack's water a full number might only change Jill's by a couple of tenths. That's why, if you feel it necessary to closely monitor pH (I don't), you should get a test kit so you can actually measure how much of your chosen acid it takes to lower your tap water to it's target pH so you can add that amount of acid each time you water.

Al

You need to be careful which MG fertilizer you use for blueberries. If it contains nitrogen from a nitrate source, don't use it. It will kill the blueberries.

I got some MG MirAcid to try on mine and doesn't contain nitrate nitrogen, so I hope it will do a good job. It looks like it contains some trace elements, too.

You need to read each label and not take it for granted it's all right for BBs.

Vivian

I have some Miracle Gro Azalea-Camelia-Rhododendron plant food, haven't been able to find Mir-Acid for years. I mixed up a weak batch, 1 tbsp in 2.5 gals water and I'm trying it on two of the blueberry plants. It uses urea and there is no mention of nitrates in the ingredients list. Interestingly, when I check the pH of the mix it was higher than my straight water (7 vs 6.5 or so). I'm using cheapo pH strips but it was clear that the mix produced a strip that leaned towards yellow-green, while the tap water strip showed an orangish color.

I see its 30-10-10 compared to Miracle Gro 24-8-16, so perhaps the Miracle Gro with added vinegar is a better solution.

How often would I fertilize the blueberry plants using the weak solution I mentioned?

Hi @jbclem how did this (MirAcid + vinegar) turn out?