Lee Senior says getting an early start to growing tomatoes is easier than you think…

If there is one greenhouse crop that everyone will have heard of, it is bound to be tomatoes. And while not everyone likes the plants and their pungent foliage, they are surely the nation’s most commonly grown greenhouse crop. Perhaps one reason is that tomatoes are not particularly difficult to grow. As a horticultural college student, I quickly learnt that the seeds can be sown early in the year, if you can provide the correct conditions. Tomatoes are always one of the first seeds I sow in the New Year, as I don’t mind giving them the extra care they need.

Tomatoes originate from South America and therefore they need warm frost-free conditions to grow successfully. In the UK that invariably means growing them in a heated glasshouse or polytunnel until the end of May when the risk of frost passes in the UK.

The optimum temperature range for seed germination is 18-22C (65-71F). Germination takes place typically between 7-14 days within this temperature range. Cherry tomato varieties make great pot growing plants. Usually the warmth required can be achieved on a south-facing windowsill, or more reliably by utilising a radiator at home or by using an electric propagator.

We are only limited by our imagination and I’ve even heard of centrally heated kitchen and bathroom floors being used too. This is fine for the sure-footed! More erratic, slower germination (2-3 weeks) should still take place within a lower temperature range of 15C-18C (59F-65F).

Tomatoes could have been sown indoors from early January if you can provide heat for germination, and critically enough light for the seedlings to develop.These days it is easier than ever to supplement early season natural light with artificial lighting for plants, both at home and in the greenhouse. It is important that the young plants do not become too leggy. Turning the pot a quarter turn regularly can help as does keeping the glass clean. As spring draws closer in February, natural light levels gradually increase and slowly the need for extra lighting diminishes. If you can’t provide the warmth needed for germination, tomato seeds can be sown in a cold greenhouse from early April, if the weather is warm enough. Pot the tomatoes on when the first true leaves appear and handle the young seedlings by the leaf rather than the stem. Aim to keep the plants on the dry side during cold spells and do try not to let the temperature drop below 10C (50F) for any length of time.

This article extract was taken from the Spring 2024 edition of The Country Smallholder. To read the article in full (covering outdoor tomatoes and choosing a variety), you can buy the issue here.

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