Why Tomato Blossoms Fail to Pollinate and Produce Fruit

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.

Lots of Blossoms But Not Much Fruit – What’s Happening?

Following is a seemingly simple question, the answer to which is very important to having a successful garden. To answer it properly is not so simple, but it is worth knowing, so I invite you to pay close attention to each element of my response.

Q. I have hundreds of blossoms on my tomato, squash and etc. plants yet very little fruit. I have observed that there are no bees around. Is this normal? What can I do to correct this situation?

A. The lack of pollinators is rarely a problem for tomatoes because their blossoms are “perfect”, meaning they contain both male and female parts. Even a gentle breeze or movement of the plant stems will allow pollination to occur.

Squash can be pollinated by hand quite easily, so long as you can find both male and female blossoms . You must take a male blossom – which is the one WITHOUT a small fruit forming behind the flower – strip the petals off, then touch the tip, or stamen, to the pistil, or tip of the female blossom. One male can pollinate several females if necessary.

This must be done in the early morning, when both blossoms are fully open, or the female won’t be receptive to pollination.

Next let’s consider the bee situation. Many places in the country are currently experiencing a severe shortage of bees. Diseases have ravaged many thousands of hives, and this is a good part of the reason honey is SO expensive lately.

First off, don’t use pesticides in your garden. They will very often kill the beneficial insects along with the problem ones. If you MUST spray a pesticide do it in the heat of mid-day when there is little or no wind. This is when bees and other pollinators are least active. And use the least toxic product possible that will accomplish your objective.

Attracting pollinators to your garden may be more difficult than just pollinating the squash yourself. Some people even resort to buying a beehive and placing it near their garden.

Many people also plant flowers near their gardens in hopes of attracting bees, etc. For maximum effectiveness you need to plant them in several bunches, rather than single flowers here and there. Flower colors that particularly attract bees include blue, purple, violet, white, and yellow.

Native plants are said to be much more attractive to native bees than exotic flowers. They are also well adapted to local growing conditions and require minimum attention.

Again, for maximum effectiveness, include several plant species that flower at the same time – to increase the number of bee species attracted to your garden – and plant a sequence of plants flowering through spring, summer, and fall, so that you attract a range of bee species that fly during different times of the growing season.

Another factor that could account for having very little fruit on plants is the temperature. This question was asked during the first week of August, which is usually the hottest time of the year.

Extreme heat is often the cause of plants not being able to set fruit. They like temperatures below 90 degrees Fahrenheit, and when it’s above 95 there is very little fruit-set.

Also, unless night-time temperatures are at least 15 degrees lower than daytime temperatures some plants won’t set fruit.

To mitigate the heat problem consider applying partial shade to your plants during the few hottest hours of the day. This is best done by placing a 25%-35% shade cloth directly above the plants, such that it shades only during the hours from 11 A.M. to 3 P.M.