Having your soil tested would be the best idea. It is hard to pinpoint the problem without knowing the ph balance of your soil. Like Jeannette posted, your local university extension service or a local agricultural office has kits that you fill with soil and send in for analysis. They will tell you exactly what your soil needs to be healthy. It is probably the most cost effective solution because you don't want to spend money on things to amend your soil only to find that it doesn't work.
Also try composting your kitchen scraps, small twigs and plant debris (healthy - not diseased and without seeds), newspapers, brown paper bags, coffee grounds, used teabags, cardboard, etc. to create a rich and nutritious amendment for your soil. Your plants will love you for it!
Testing your soil: Contact your local County Extension Service. They have a kit that you can purchase (a couple of bucks). The directions come with the kit an it explains how to take samples of soil from your garden. Return it to the address listed on the kit, they will check the soil and send you the results and how to amend your soil. Jeannette W. Palm Beach FL
Check for very tiny red spiders on your plants. They will cut the blooms off and you'll have no produce. You can also use 1 tablespoon of Epsom Salt to a gallon of water to get rid of the red spiders. They sound like they might need fertilize or they might have a blight of some kind. Sorry I couldn't be of more help.
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