What form of sulfur should we add to our vegetable garden to decrease the pH level?
Our vegetable garden shows too high levels of pH (7.3-7.5) in all the beds and rows according to soil samples processed by UMaine Extension. We began to establish the garden nearly 50 years ago on a glacial moraine. The soil type us predominantly Naumberg Sand and Gravel. The advice from UMaine Extension was to “Apply 15 lbs. of elemental sulfur/1000 sq. ft. to lower pH to 6.5. Till in well.”
Our question is what precise form of sulfur should we purchase, and when apply? A farm shop has several varieties, some apparently an insecticide. We don’t use a tiller, so would we simply dig it in with shovels? Would our garden likely become much more productive, given the high current range of PH? And if production will increase with added sulfur, would we see a change within a season or would it take several years?
First, let me offer you kudos for getting your soil tested before adding any amendments. All too often, gardeners add things willy-nilly in the garden and if they don’t know what the starting point is, they can often wind up causing more trouble than they fix. You are already using science to your responsible advantage.
What you are looking for is sold as “elemental sulfur.” If it doesn’t say that specifically, check the ingredients, as you just want sulfur–you don’t need to add any insecticides into your garden soil, based on what you’ve told me. Sulfur can burn plant foliage in the high temperatures of summer, so you’re going to avoid that risk entirely by adding your amendments early in the spring, just as soon as you can work the soil without damaging its texture. If you aren’t using a tiller, I would fork it into the top 6-12″ of your garden beds (if left on the surface, it will eventually help with the pH, but it may also blow away in the wind or wash away in sudden rainfall).
Unfortunately, while sulfur is pretty non-toxic, inexpensive, and easy to add, it’s not a quick fix, as it must undergo biochemical oxidation in the soil in order to transform into a form usable by plants. Under ideal conditions, your pH might change in a single season, but it will probably be the second season before you notice. That said, while your pH is too high, it isn’t crazily so–you will notice an uptick in both productivity and general health of your plants, but it won’t generate shockingly higher yields.