The following is adapted and condensed from the book Let’s Grow Tomatoes, by Dr. Jacob R. Mittleider.
In addition to the 13 essential mineral nutrients man can provide, plants require water, exercise, anchorage, sunlight, warmth, living space, and protection from extremes in weather, disease, and insects. This would indicate that there are many possible causes for your garden to fail at producing a crop, and this is true. However, there are a few common problems which deserve special attention.
Nematodes – Soils everywhere are infested with these tiny eel-like worms that eat into the roots of plants and live off the plant juices. Infected roots have irregular brown-colored swellings which appear like rough knots. Infestation can be serious without affecting plant color or other visual appearance. Failure to set fruit is usually the first indication the grower has of the problem. Producing fruit places a heavy load on the plant, and if nematodes are present the plant will abort the fruit in order to stay alive. Because the plant cannot expel the nematodes it continues the same process, with new stems, leaves, and flowers, and being unable to support the burden of producing fruit, it aborts the new fruit at or near conception.
Lack of complete and balanced fertilizer – A proper balance of all 13 nutrients is essential for optimum performance, and a deficiency in even one nutrient can result in crop failure. See the 3 volume set of The Garden Doctor books by Jacob R. Mittleider for details on deficiency symptoms and solutions.
Insects and soil maggots – Tomato fruit worms eat the new fruit as it is formed, and thrips eat the pollen and prevent pollination. Soil maggots eat the stem below the soil surface and weaken the plant similar to nematodes. A regular dust or spray program is necessary to control the first two, and a Diazanon drench will eliminate the soil maggots.
Weather Problems and air movement – Temperatures above 95 degrees Fahrenheit will cause tomatoes to stop setting fruit, and below 50 degrees there is almost no plant growth, so protecting against those extremes is very important.
Heat can be reduced by using shade cloth, and plastic coverings can increase temperatures – at least during the day. However, care must be taken to avoid losing essential sunlight, since that is the number one law of plant growth. Fruiting crops will not produce without direct sunlight for 6-8 hours each day. 25-35% shade cloth that shades the plants during the hottest part of the day is recommended where daytime temperatures are consistently above 100 degrees Fahrenheit.
Some growers believe that greenhouse-grown tomatoes may fail to pollinate if there is no air movement. They try to resolve this by vibrating the vines occasionally. Dr. Mittleider has never experienced difficulty from this source, and our experience has been that pruning, guiding plants up the baling twine strings, and removing sucker stems provide adequate movement for self-pollination to occur (the flowers are self-pollinated because tomato flowers are “perfect”, including both male and female parts).
Diseases – If your tomato plants are suffering the effects of disease the symptoms are usually very evident, and are not limited to pollination or fruit set to know that something is wrong. Rotation is sometimes recommended to minimize problems, however the family garden is rarely large enough to allow the separation needed to be very effective. Fungus diseases can often be controlled by a good and timely spray or dusting program. The chapter on Diseases in Let’s Grow Tomatoes is recommended for a more in-depth discussion of this subject.
Let’s Grow Tomatoes is available as a digital download at Food For Everyone Foundation – http://www.growfood.com/Shop.