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John Fulton


John Fulton
Former County Extension Director



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In The Backyard

Horticulture columns and tips done on a timely basis

Steering your tomato plants for optimum growth and yield


According to the National Gardening Association, tomatoes are the most popular vegetable grown in home gardens. And, if you have ever grown tomatoes, you know that a well-grown tomato can produce an abundance of fruit. But have you ever had a year where you had huge, leafy plants, but the tomatoes were fewer and smaller than expected and took longer to ripen? If so, you were experiencing an excessively vegetative tomato plant.

The key to successful tomato growing is to be able to balance vegetative and generative (reproductive) growth. A plant that is vegetative is using the products of photosynthesis to grow more plant (stems and leaves) while a generative plant is using these products to grow more fruit (most effort put into flowers, buds and fruit). Fruit size and yield will decrease if your tomato plants become either too generative or vegetative. Vining crops like tomatoes produce vegetative and generative growth at the same time while plants like spinach are vegetative one day and reproductive the next.

What are the clues that your plants are telling you about their growth? What do you need to look for? The table below lists the plant characteristics for reproductive and vegetative growth. To assess if your plants are in a vegetative state, look at the top seven inches. Do you have a fat stem six or seven inches below the tip? An aside, in order to use this to assess growth, you will need to notice how things change over the course of the season as there are varietal differences in stem size (grape vs. beef). Other signs that a plant is vegetative are thick and curled leaves and flower trusses (the branch of yellow flowers) that are thin, long and stick upwards. Also, vegetative tomato plants have flowers that may be a pale, light yellow and the open flowers are father down the vine away from the growing point. Fruit are small, poorly shaped and slow to ripen.

Table 1. Steering the tomato plant: reproductive versus vegetative growth

Characteristic

Generative (reproductive) Growth

Vegetative Growth

Leaves

Flat and open, light green, soft

Curled, thick, dark green

Flowering

Close to the top of the plant

Flowers open fast and uniform

Rapid flowering within truss

Further from the top of the plant

Flowers open poorly; sepals stick

Poor uniform flowering within truss

Flower Color

Dark yellow

Pale, light yellow

Truss Stem

Thick, sturdy, short and curved

Thin, long and sticking upwards

Fruit

Large, many, good shape and fast

development

Small, few, poor shape and slow

development

Jensen, Merle H. "Steering your tomatoes towards profit." Greenhouse Crop Production and Engineering Design Short Course, Tucson, AZ (2004): 3.

The signs of a generative plant are basically the opposite of a vegetative plant. The stems are thinner at the top of the plant. The leaves are flat and open and the flower trusses are shorted and curved, arching out from the plant instead of sticking upwards. Flowers are dark yellow and at the top of the plant.

Ok, so you are now able to assess the state of your tomato, but what can you do to influence their growth? If plants are vegetative, reduce or forego fertilization. Adding fertilizer to a plant in a vegetative state will only encourage them to produce more leaves at the expense of fruit. You could also manage your watering by allowing your plants to dry out and water more thoroughly when you do water.

Remember, balance is what you are looking for.

For more information about growing tomatoes, check out the Illinois Vegetable Growing Guide at http://web.extension.illinois.edu/vegguide/grow_tomato.cfm




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