This is my first year growing a big vegetable garden and I'm learning as I go along. When we first constructed the garden in February, we used 6" of garden mix topped with 1" of compost for the rows. I naively assumed this would be plenty of nutrients for our plants, and moved forward with sowing seeds and transplanting seedlings without testing the soil. When I noticed plants were growing very slowly, I tested the soil with Rapitest and found low (basically depleted) nitrogen. I added some Down to Earth All Purpose fertilizer and applied some bat guano. I noticed an improvement, but about 10 days later the plants' growth slowed down again. I tested the soil again, and the nitrogen levels had increased from depleted to deficient. I again added bat guano and saw nearly instant improvement on my lettuce (went from yellowish to green). Am I stuck in this perpetual cycle of adding nitrogen fertilizers and re-testing, or is there a more low-maintenance (and hopefully low-cost) solution? We have a drip irrigation system, and fertigation would be an option, but I was wondering if it was too late to add composted manure to the rows? Thanks so much for your help.
Certified GKH Gardening Expert
You can add amendments to the soil at just about any time. Just don't let the compost come into contact with your young plants.
Did you happen to test the pH of the soil while you were testing fertility? Sometimes a very high pH will lock out nitrogen, and it will be completely unavailable to the plant. You can lower this with iron sulfate, as well as applying just a little dolomitic lime to keep it stable. Just don't overdo the dolomite, as it will raise the pH if you use too much. Sprinkling an 8 oz. cup's worth evenly around each plant to about a foot out should be plenty.
About a week after adding all of your amendments, plus the few that I have described, it should remain a lot more stable. A photo of the area can help me too. Sometimes other trees, even if 50 feet away, can cause damage to garden plants. Trees like walnuts, pecans, and other related members are toxic to many plants.