I live close to the pcific ocean, just a few steps outside my garden. The soil is black sand and I plant seeds that are4 suitable for my area. Many tines they grow well but later on when they are six or seven inches high they suddenly wilt and dont recover. People have told me that its because there nematodes in the soil (I can get nematicides here) and others tell me to wash the soil with boiling water before planting. I noticed some varieties it does not seem to bother so I suppose they are immune to that. I would appreciate any advice