Is it really important to give blueberry plants acidic soil?

Question

I have two blueberry bushes which I planted at the end of the summer. Although I had read online that they prefer acidic soil, I didn't have the time to check the pH of our soil, and go out to buy something to make it more acidic. My bushes seem reasonably healthy (although perhaps suffering from a lack of water), but I wanted to know how important it is to give them acidic soil?

There are a few parts to my question:

1. Is this something to bother with, or just something to do if you are a really serious gardener?
2. Does the soil acidity affect the growth and health of the plant, the fruiting (quantity and quality), both, or neither?
3. If you would recommend adding something to the soil to lower the pH, what?

Thanks for your help!

Answer 1

Blueberries certainly like acidic soil (about 4-5 pH) and is quite necessary for a healthy plant with good fruit production. This is not just for "serious gardeners", but is something that blueberries need. While the plant might grow in neutral soils, the fruit production might be low and the leaves generally sparse. I can tell you from experience that my blueberry bush did not do well before I decreased the pH of the soil.

You can increase the soil acidity in a few ways:

• mulch the plants with pine needles, if that's easy to acquire in your area.
• work peat into the soil around your plant and in the top couple of inches (take care not to damage the roots, they're shallow) and then cover with mulch.
• use a soil amendment mix that's commonly sold for Azalea/Gardenia. These are two other plants that require acidic soil and it's common to find mixes for these. These work very well for blueberries too and is in fact, what I use since I can't find either of the two above all that easily.
• If your soil is already moderately acidic, you needn't do any of the above, but use composted coffee grounds every few months to maintain the acidity.

In addition, blueberries also need well drained soils. As I've mentioned above, they have very shallow fibrous roots and if your water doesn't drain away, it will cause root rots. So never plant blueberries in the low points of your garden, where water is more likely to collect.

Also, you'll need to water regularly too, because shallow roots can't reach deep down for water. Use a thick layer of mulch to conserve moisture and water it often enough such that the soil is always moist and never let it dry out for too long.

Answer 2

A pH of about 4.5 is required for blueberries to do well. (Some sources say as low as 4.3, some as high as 5.0; most sources say they do well between 4.0-5.5, which is a fairly large range.) At higher pH, the bushes will have an iron deficiency; see the photo and discussion on this page for iron deficiency caused by high pH.

The best way to adjust the pH depends on your soil type and the starting pH. Blueberry plants live a very long time, so it's worth the up front effort to prep the soil so they can thrive. Once they're planted, it's more challenging to alter the pH.

First, get your pH tested. In my opinion, the best thing you can do is to get a professional soil test -- contact your county extension service in the US. When I get my soil tested, the form has a checkbox for blueberries, and the results will come back with recommendations for fertilizer and pH adjustment.

• For a temporary effect you can water the plants weekly with a vinegar solution (2 tablespoons per gallon of water). This won't alter the soil pH though, you need a long term solution.
• You can work in peat moss to make the soil more acidic. On an established planting, you can't work in the peat without damaging the roots. Top dressing with peat will have some effect.
• You can apply sulfur to lower the pH.
• Use a high acid fertilizer when you apply fertilizer. You can find appropriate fertilizer at your garden center. Look for "acid loving plants" on the label; it will usually list blueberries on the back but sometimes the front will just say for azaleas/rhododendrons.
• Top dress with coffee grounds. This will also add some nitrogen.
• Mulch with pine needles, pine shavings, or other acidic mulches.

Once you get the pH to the proper range, you will need to maintain the level. If the area where you live has naturally alkaline soil, it will revert back to high pH over time. Continue to fertilize with acidic fertilizer and use acidic mulches and top dressings.

Certain soil types resist changes in pH more than others. (If you want to get technical, look up "CEC", Cation Exchange Capacity.) Basically, sandy soils are easier to modify. Clay soils are harder. Soils with high organic matter are even harder. As the pH gets lower, it's easier to modify. So if you have sandy soil with a pH of 5.5, you will have to do much less work than if you have loamy clay soil with pH of 6.5. (And this is why I recommend a professional soil test from a local lab -- they can give the best recommendations that are most suitable for the soils in your area.)

Answer 3

Pine needles will not acidify your soil! They are slow to decompose, and even after they do, dead pine needles are pH neutral and thus have no effect on soil pH. It's amazing how many people, including gardening experts, believe this myth! (See Garden Myths-pine needles.)

That being said, pine needle mulch is a great mulch for any plants, regardless of their pH preference.

Likewise with coffee grounds (see Garden Myths-coffee grounds). They can add fertility and boost organic matter, but note that composting coffee grounds before adding them to the soil is advisable, as uncomposted grounds contain carcinogens!

Also, see Garden Myths-increasing soil acidity for a discussion about the relevance of soil type to your acidification strategy, and Wikihow acidifying soil for further instructions on acidifying soil.

Answer 4

An additional method for acidifying soil is elemental sulfur. Start with about 1 lb S in the form of powder per square yard. The reaction is slow -- actually the sulfur is eaten by a bacteria, and converted to sulfuric acid. It takes about 3 months. The sulfur has to be worked into the soil No bacteria on the surface. Once you get the pH down,you can maintain it with periodic doses of prilled sulfur at a higher rate, but less often. (about every 5 years)