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What to do when vegetables go vegetative

Cold temperatures, low light have changed direction of growth.

March 26, 2019  By Dr. Mohyuddin Mirza

Cucumber [left] and tomato [right] plants experienced rapid elongation. What happened?

Looking at these photos, do you know what happened to these cucumber and tomato plants? Growers were expecting a compact and strong plant, but within a short span of a few days, the plants were already touching the wire, internodes were unusually elongated, and weak sets of leaves developed, looking thin, misshapen and not fully expanded. The first cluster of tomatoes appeared five feet on the stem.

These pictures were taken in the third week of January. When seedlings were planted on the blocks, they were about three weeks old. The plants grew very fast. Although the flowers were set after about five to eight leaves, the stem elongated and one could see weak flowers developing towards the tops of the plants. Weak flowers do not show a typical deep orange colour, do not appear to have vitality and strength, and have weak stems (pedicles). There will be a delay in harvest and first fruit in tomatoes will likely be showing unbalanced shape (catfacing).

What to do when light is low and water and nutrients are unlimited
It is about managing electrical conductivity (EC) in the growing medium. Aim for higher EC values, over 3.5 mS in cucumbers and over 4.0 mS for tomatoes. When I asked a grower to check the EC in rockwool cubes, he told me that it was 4.0 mS in the squeeze from the cubes in which the seedlings were growing.


Use feed EC of around 3.0 to 3.5 mS and let the leach go over by 1.0 mS. In this manner, the plant will stay compact and will become generative quickly. There will be good balanced growth. Many growers use potassium sulfate 0-0-50 to raise the EC. In this way, the nitrogen to potassium ratio changes from 1:1.5 to almost 1:3.

If plants have stretched like what’s shown in the pictures, then remove the first cluster in the case of tomatoes. Remove any weak flowers as early as possible for both cucumbers and tomatoes.

An important note: When tomato fruit starts sizing up, start dropping the EC by 0.5 units. EC management by light can be used during cloudy and dark days, keeping the growth in balance. During summer periods, used lower EC values.

Mohyuddin Mirza, PhD, PAg, is a greenhouse specialist and consultant. Questions or comments? Contact him at

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