Tomatoes, although technically short-lived perennials, are treated as annuals and raised from seed each year. They are sub-tropical plants that require a consistent temperature of at least 55ºF in order to germinate successfully, but a temperature of 70ºF will produce much quicker emergence and is generally preferred. Given warmth, good light and a damp friable growing medium tomatoes are very easy to raise from seed.
For most gardeners, even those that live in warmer districts where tomatoes are cultivated outdoors from their very early stages of growth, it is usual to start the seeds off in pans or flats of compost under controlled conditions. Tomatoes can be sown directly into the open ground, where the climate and soil conditions are suitable, but much better establishment of better quality plants always results from controlled seed raising and growing the seedlings during their initial stages of growth in independent modules or pots. Transplanting is easier and establishment is rapid.
As tomato seeds are large enough to handle individually, it is best to space them out on the surface of the prepared compost so that when they germinate they do not crowd each other. Also when they are pricked out there is no undue disturbance of the fragile root systems through them having become entangled with each other. A properly formulated seed compost is essential. A sterile medium of a texture and quality that will offer the best start for the germinating seeds.
There are a number of different composts available, but for the hobby gardener a good soil-based seed compost is to be preferred to a soil-less one. Soil-based composts, although generally slower to warm-up, and often slightly impairing the speed of seed germination, usually yield the finest and strongest plants, especially for planting directly into the garden outdoors.
Plants that have been raised in a soil-less compost, which almost always comprises a high proportion of friable peat, often take time to adapt their roots to the more hostile and less forgiving medium of natural garden soil when planted in their permanent positions. Sometimes a check in growth occurs while the roots adapt, resulting in an impairment in the plant’s development.
Soil-based composts also overcome the problem, commonly encountered with tomato seedlings raised in a soil-less medium, of the seed coat sticking the two seed leaves together, often making them inseparable without causing damage. The seed coat is generally detached by the coarser soil-based medium as the seedlings emerge.
Once the seedlings have their two seed leaves fully expanded they should be pricked out, ideally into individual modules or small pots, although they can spend two or three weeks pricked out into flats in order to save space when this is necessary. Like all seedlings, tomatoes that are raised in this manner are vulnerable to damping off disease. This causes the seedlings to rot at the base of the stem and collapse. The routine use of a fungicidal treatment is to be recommended.
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