When tomato seeds are sown too early, they will often become tall and spindly, or ‘leggy’ as we refer to them. This is where they reach up to the sky to try and get light. As soon as the weather starts to improve, many of us become very keen and sow seeds before they should be sown. Leggy seedlings are often weaker and much easier to break when you transplant them. With some plants, there is no cure to legginess except to start again, but you can usually rescue tomato plants due to their unique manner of growing.
The most common cause of leggy seedlings is lack of strong, overhead lighting. Tomato plants become long and spindly when they are reaching for the light. If the light only comes from one direction, then your seedlings not only become leggy, but will also lean towards the light. Tomato seedlings benefit from being rotated every day so that the lean does not become too pronounced. This results in stronger, straighter stems, which are much easier to transplant.
When tomato seedlings are not transplanted soon enough and left for too long in shallow containers, their energy is put into stem growth rather than creating a strong root system. Prevent the roots from becoming stunted by transplanting your tomato seedlings regularly to larger containers, particularly if you have started them off in a shallow seed tray. Keep repotting until they are in their final pot. This gives the roots plenty of room to grow so that the stem grows normally.
Another cause of leggy plants is too much fertilizer in the soil. If the levels of nitrogen are too high, then the seedling will become leggy. When feeding your tomato plants, it is best to use a specialist tomato fertilizer rather than a general purpose one to ensure your plants get the right balance of nutrients.
If your tomato seedlings do become leggy, then all isn’t lost. Unlike plants such as cauliflower, tomato seedlings can be rescued because they grow roots from the main stem.
Before transplanting, remove the bottom few leaves and then plant the seedling more deeply than normal in the new container. Leave the top few sets of leaves exposed above the soil. The plant will develop new roots from the main stem and the stem will become thicker and strong. Place the seedlings in a position where they get full sun all day, or invest in some grow lights to place above your plants to encourage them to not become too leggy.
If an established, or larger plant becomes leggy, then they can often be saved by pruning them well and pinching the top off the plant. This encourages the plant to grow bushier and put its energy into something other than growing tall.
Leggy tomato seeds are not the end of the world. If you repot them deeply and place them somewhere with a more consistent light source, the plants can be rescued and will grow into healthy, productive adult plants!