Answer: Without more information on your growing practices (soil improvement, fertilizing), it's difficult to give an answer, but it sounds as if one problem may be that your soil is depleted of nutrients. I think a soil test is a good idea. I'll also include some info below on improving soil and fertilizers.
Another potential problem is lack of pollination. There aren't as many honeybees around due to variety of factors, such as the public's fear of "killer bees," which translates into many bee hives being exterminated. In addition, the bee population has been decimated by a mite problem. You can hand pollinate squash blossoms yourself by taking a small artist?s paint brush or Q tip and rubbing the pollen from the male (without a small fruit behind the flower) and into the female (with a small fruit behind the flower).
Also, plants need phosphorous to produce flowers and fruits. You might want to use a side dressing of fertilizer high in phosphorous (the middle number) or an organic source, such as bone meal. Scratch it into the soil to the side of the plant's roots.
It's also important to rotate crops every year so crop-specific diseases, such as wilt, and insects don't have a good chance to build up in the soil.
Vegetable crops and annual flowers are heavy "feeders" and no matter how fertile the soil, it must be continually improved to maintain it. Add a 2-3 inch layer of compost to your soil several weeks before planting to greatly improve it's fertility.
Continue to add lots of organic matter each year, which over time will not only improve your soil's fertility and drainage, but will also increase it's ability to retain moisture and nutrients. It also provides food for earthworms and microorganisms that do the soil-building process. You can never add too much compost!
In sandy soils, compost improves soil fertility, water and nutrient retention. meal, fish emulsion, seabird guano.
Phosphorous: bone meal, rock phosphate
Potassium: greensand, seaweed, kelp
After planting, add a 1-2 inch layer of mulch. Mulch is great to help retain soil moisture, reduce weeds, and as it breaks down it provides nutrients to the soil. Any organic matter can be used as mulch. Try compost, bark, wood chips, straw, or pine needles.
In clay soils, it improves drainage. Add a 4-6 inch layer of compost and incorporate it about 12-18 inches deep. Each planting season, add more compost. You may want to incorporate a balanced fertilizer (e.g., 10-10-10) or add organic fertilizers such as fish emulsion, bone meal, and seaweed/kelp before the initial planting. Follow package instructions. If you prefer organic fertilizers, you may need to use three different sources, since they seldom come mixed together the way non-organic fertilizers do.
Side dressings of fertilizer are often beneficial during the growing season, but you shouldn't have to fertilize as frequently as you water. Perhaps once every two weeks at most. As your soil fertility improves, this won't be needed. Examine your plants to see what might be deficient. Slow growth and/or yellowing leaves is often a sign of lack of nitrogen. No flowers or fruit set means phosphorous is missing. Always ensure that the soil is moist before fertilizing, and then water the fertilizer in well afterwards. This helps prevent "burn." If you use a granular fertilizer, scratch it into the soil at least 4 inches to the side of the plant to prevent burning roots.
Here's a little background on fertilizers for your info: You probably noticed that fertilizers have 3 numbers on the container. These numbers refer to the percentage of nitrogen (N), phosphorous (P), and potassium (K) in the fertilizer. These 3 elements are referred to as macronutrients because plants need them in fairly large (i.e., macro) amounts to thrive. How these elements interact is complicated but in general terms, nitrogen produces lush green growth, phosphorous helps strengthen stems and produce flowers (and eventually fruit), and potassium keeps the root system healthy.
Here are some organic sources of nutrients:
Nitrogen: alfalfa meal, blood meal, coffee grounds, cottonseed
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