Answer: A couple things come to mind. Lots of foliage at the expense of flowers and fruit can signal an overabundance of nitrogen and/or not enough phosphorous. If you have no flowers, this would be a likely problem. Here?s some basic info on fertilizer and nutrients that plants require. The 3 numbers on a fertilizer bag refer to the percentage of N (nitrogen), P (phosphorous), and K (potassium) in the bag. There are different formulations for different purposes. In general terms, nitrogen produces lush green growth, phosphorous helps strengthen stems and produce flowers, and potassium keeps the root system healthy. If you're applying fertilizer to fruiting (e.g., tomatoes) or flowering plants, you're not as interested in the plant developing leaves as you are in it flowers and fruit, so you'd use a formulation lower in nitrogen and higher in phosphorous, such as Miracle-Gro's Plant Food at 15-30-15. Bone meal is an organic source of phosphorous.
Organic sources of nutrients:
Nitrogen: alfalfa meal, blood meal, coffee grounds, cottonseed meal, fish emulsion, seabird guano.
Phosphorous: bone meal, rock phosphate
Potassium: greensand, seaweed, kelp
If your plants have flowers, but don't set fruit, it's likely that the flowers aren't being pollinated at all. There aren't as many pollinators (bees, etc.) around as in past years. Try gently tapping and shaking your plants in the early morning, or hand-pollinate with a Q-tip to see if you can get some fruit to set. Good luck!
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