One of the primary causes for poor production of summer vegetables is over-fertilization. Fruiting plants need a balance of nutrients to produce well. Too much nitrogen, or a fertilizer weighted too heavily in nitrogen, causes leafy growth at the expense of fruit production. Leafy growth is fine for cool season vegetables, but warm season fruiting types, like pepper and tomato, suffer from excessive leafy growth. Besides chemical fertilizers, it's also possible to overdo it with organics such as manure. It's better to add fertilizer as-needed, rather than starting out with too much. If over-fertilization is suspected, nitrogen can be leached out of the root zone of plants by watering heavily.

Vegetable production also suffers from adverse temperature conditions. Tomato and snap bean will drop their blooms when temperatures exceed 95 degrees. Blossom drop is more of a problem in tomatoes when night temperatures remain high, 75 degrees and above. That's why it's so important to plant tomatoes out early in the spring to maximize their productivity. Cherry tomatoes are the exception as they will set fruit over a wider temperature range than most large-fruited types. Cherry tomatoes will fruit throughout the heat of summer, even here in Tucson.

Corn is another vegetable adversely effected by high temperatures. The corn tassel (pollen producing part) is often killed when temperatures are above 100 degrees. Injury to the tassel will prevent development of kernels in the ear.

Water plays a crucial role in fruit production. With summer vegetables, blossom and fruit drop is commonly a result of moisture stress. Be consistent with watering. Maintaining an evenly moist soil in the vegetable garden encourages the best production. After fruit have formed, continue with consistent watering. Blossom end rot, common on tomatoes and peppers is a result of fluctuating levels of soil moisture.

It is common for summer squash plants not to produce, or to produce poorly. This is because of insufficient pollination of the female flowers. Both male and female flowers are produced on the same squash plant. Sometimes many more male flowers are produced and few if any female flowers appear. At other times many more female flowers are present, but male flowers are scarce. Pollination from male to female flower fails to happen, and no squash are formed. Hand pollination can be carried out. 

Male flowers from one plant can be used to pollinate female flowers from another, or of the same plant. Female flowers can be identified by the miniature squash (unfertilized embryo) attached under the flower. Male flowers have no such attached miniature squash. To hand pollinate, a male flower is removed and the pollen producing anthers in the center of the flower are rubbed onto the stigma of the female flower to achieve fertilization.

Finally, some vegetables fail to fruit or fruit poorly because they are not adapted to the intense heat and sun of the desert. Bell peppers for instance are not adapted to our summer growing conditions and do poorly, but chili peppers love the heat! Many garden seed catalogs have a selection of vegetable varieties that will tolerate intense summer heat. Early ripening varieties are also well suited to the desert as they will mature before the heat of summer sets in.

Local garden centers and nurseries also have good selections of heat adapted varieties. 

Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona 626-5161.  Material originally appeared in Arizona Daily Star gardening column, on May 2, 1999
Return to index