When we first opened the garden, we had the soil tested, and the pH (acid/alkaline balance) was very low, about 5.8. We added 170 lbs of lime when we dug it up – about 17 lbs/100 sf. We checked the soil again on June 26 in a few spots around the garden, and the pH was around 6.6, which is just about perfect for most vegetables. It takes a while for the lime we added in April to change the soil chemistry, so we wanted to verify that we’d added enough. Every time it rains, the soil becomes a little more acid, so we need to keep checking and adjusting throughout the season.
We lightly dusted lime around the plants that have a sweet tooth (cauliflower, broccoli, tomatoes, beets and greens). Some plants (potatoes, eggplant) like it a bit more acidic, so we did not add any lime to those beds.
We used calcitic lime (plain ordinary powdered limestone, or calcium carbonate) because it adds a quick shot of calcium to the soil, to help prevent blossom end rot on the tomatoes.
Soil pH is important because plants won’t absorb nutrients from the soil as well if the pH is too high or too low. A good introduction to soil pH is here, on the UMass Extension web site.
Did you know that farmers used to check their pH by tasting the soil?