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Growing Tomatoes from Seeds

Tomatoes are one of the most popular vegetables (or should that be fruit?) to grow from seed in your own garden. Rewarding you with a bounty of tasty tomato crops that are much better tasting than the bland commercially grown tomato varieties bought in supermarkets. 

Planting tomatoes in a container

Tomatoes are easy to grow & might surprise you at how easy they are to grow from seed. With a wide range of tomato seeds to choose from, ranging from small sweet cherry varieties to large beefsteak ones, we will show you how to grow tomatoes and get the best results.

Sowing Tomato Seeds

Below are some useful tomato growing tips; from how to plant tomato seeds and grow the very best tomatoes, to growing tomatoes in pots.

Seeds can be sown from January to March. Using a multipurpose soilless compost or a good quality seed compost, fill seed trays or 7.5cm (3″) pots, leaving a ½” gap at the top. 

Sow the seeds thinly in the trays or singularly in the pots. Cover the seeds with a thin layer of compost and water. Place in a propagator or cover with cling film and stand on a warm, sunny windowsill.

Temperature for germination should be approximately 20o-25oC (68o-78oF) but check the seed packets for individual varieties. Too high a temperature in the early stages leads to spindly growth and unhealthy plants.

Once the seeds have germinated, usually 7-14 days from sowing, remove the cling film, or take them out of the propagator and return them to the windowsill. If growing in trays, the seedlings should be transplanted into 7.5cm (3″) pots when they are 2-3 cm tall, using a multipurpose compost. Keep the compost moist by watering with a fine rose, preferably in the morning.

Keep potting on as required until the plants are ready to plant out.

tomato seedlings
It’s rewarding to see tomato seedlings germinating

Planting out tomato seedlings

At the end of May or early June, when all danger of frost has passed, the tomato plants will be ready to plant out in their final positions. Select an open sunny position or plant into 30cm pots. Beds for the plants should be prepared well in advance, incorporating well-rotted manure or garden compost if possible, and a general fertilizer at the recommended rate of application.

Plant firmly, placing the ball of roots and soil about 25mm (1″) below the surface of the fresh compost. In beds or border, space the plants about 45cm (18″) apart, with rather wider spacing between the rows. Plants in pots will eventually need more water than those in the border, but the soil must never become waterlogged.

Tomato Veranda Red Burpee

Tomato seedlings after-care

Immediately after planting, it is an advantage to give some protection at night, either by using cloches or fleece.

Once flowers begin to appear, the plants should be fed with a liquid tomato fertilizer at the recommended rate weekly. The growing point should be removed when five or six trusses have formed, as this will encourage the fruits to swell more rapidly and mature more quickly.

Keep the plants well-watered, especially when the fruits have started to set.  Wide fluctuations in moisture supply may lead to irregular fruit growth, cracking of the skin, and dropping of the fruits.

Tomato bush varieties

Some tomatoes are described as bush varieties, and these are essentially outdoor types of early maturity and producing prolific crops.  This type of plant does not require staking, pinching-out or the removal of side shoots. These plants generally reach a height of about 38cm (15″) and are indeed relatively compact though they have a spreading habit are suitable for growing in the vegetable garden or in containers.

Plant about 60cm (24″) apart depending on the variety being grown.

The varieties Tumbling Tom Red and Hundreds and Thousands are suitable for growing in hanging baskets.

tomato tumbler plant
Tumbling Tom Red bush tomatoes

Growing tomatoes in compost bags

To secure the best results, the plants should be quite well developed and with the first flower beginning to open when they are planted in the bag.

Where the bags are to be used in a heated greenhouse having a minimum temperature of no less than 13ºC (55oF) they may be planted up in mid-March, but in unheated houses mid-April will probably be early enough, although much will depend upon the local climate conditions.

If headroom restricts the final height of the plant to 1.5m (5′) or less, (allowing 5 or 6 trusses), no more than 3 plants should be put into each bag.

Outdoor planting must be governed in some measure by local weather conditions, and late May or June will usually prove most suitable unless the situation is very warm.  No more than 3 plants should be placed in each bag.

It is recommended that a minimum space of 37cm (15″) be left between the “ends” with a 23cm (9″) spacing between double rows.

Frequently asked questions about growing tomatoes

Why are the flowers on my tomatoes dropping off with out setting?

Sometimes tomato plants produce good trusses of flowers but these wither and drop off without setting. This can be due to high or low temperatures, dryness at the roots or in the air.

Fruit setting occurs most freely in warm sunshine and in a moist atmosphere, so to aid pollination, spray the plants with water on sunny days around midday and then ventilate the greenhouse. Gently tapping or shaking the stems will encourage the flowers to shed their pollen.
If the plants are a dark, bluish-green and few flowers are being produced then they are probably suffering from an excess of nitrogen and this can be quickly corrected by feeding with a proprietary tomato food.

Why are patches on my tomato fruit not ripening?

A tomato fruit not fully ripening is due to disorders known as Blotchy Ripening and Green Back.

Blotchy Ripening is the development of unevenly ripe fruit which have green or yellow patches. In the case of Green Back the area around the stalk fails to ripen properly or remains green.

Both disorders can occur if there is a deficiency of potassium and when the greenhouse temperatures become high and the fruit is exposed to strong sunlight. Ventilate the greenhouse as much as possible in hot weather and damp down the pathway to reduce the temperature. Light shading may also need to be applied to the glass. Feed the plants regularly with a liquid tomato feed once the first fruit start to develop.

Why have my tomato plants died after developing dark blotches on the leaves?

Tomato Blight is a common fungal disease that can be serious in wet seasons but less so in dry summers. It is more likely to attack tomatoes grown outdoors although in some seasons those grown in the greenhouse can also suffer from this disease.

The first symptoms to be seen are dark brown/black blotches appearing on the leaf edges that quickly spread until the entire leaf is killed. White fluffy fungal growth may also be present on the underside of the leaf. Dark patches can also develop on the stem and the green fruit. The more mature fruit decays rapidly with a dryish brown rot which may not be visible for several days after picking.
Once blight has a firm hold there is little that can be done other than destroying the affected plants.

The variety Lizzano shows some resistance to blight. Crimson Crush is the most resistant variety available to the amateur gardener.

Why are the skins on my tomatoes tough?

The toughness of tomato skins is dependent on the way the crop has been grown. Too much heat or sunlight will result in tough skins so the greenhouse should be adequately ventilated and lightly shaded to prevent the fruit ripening too quickly.

It is also possible to produce fruit with tough skins where the plant is not growing vigorously due to low temperatures or the plants receiving insufficient water and tomato food.

Why have my tomatoes developed a brown area at the base of the fruit?

Blossom End Rot is a disorder that causes the development of a blackened leathery dark brown or black patch at the flower end of the fruit. This problem is associated with calcium deficiency and is often induced during periods of water shortage. It is important that the compost or soil does not become dry, even for short periods, and to apply water in sufficient quantities to allow it to soak right down to the full depth to which the roots extend.

Spraying at fortnightly intervals with calcium nitrate at 3 gms per litre of water (0.5oz per gallon) will help to cure this problem or you could use a proprietary tomato food that has calcium included or the Top Resist Vegetable foliar feed.

Why has my tomato plant produced a lot of lateral shoots at the top of the plant?

Occasionally the terminal shoot of the tomato plant aborts and is replaced by a number of lateral shoots. This is known as bushy head disorder. The flower truss at this point of injury is normally erect and has many branches. The leaves on the shoots produced can be mottled, malformed and have marginal leaf scorch.

This disorder often occurs from April to June in periods of bright sunshine. It is associated with high temperatures in the greenhouse resulting in the death of the terminal bud due to high leaf temperatures. Some varieties may be more susceptible to this disorder than others. Allow one of the terminal shoots to develop as the main leader which will grow on to crop normally. Remove all the other lateral shoots that have developed.

Why are the skins on my tomatoes splitting?

The splitting of tomato skins can occur quite frequently on tomatoes grown outdoors and in the greenhouse. It is caused by the onset of wet conditions following a dry spell or as a result of insufficient watering for a time. The plants become deficient in water and then with the onset of rain or an increase in water supply, the plant cells enlarge rapidly leading to the splitting of the fruit skin.

To avoid the problem ensure the roots are supplied with ample water. The addition of well-rotted garden compost to the soil will increase the moisture holding capacity.

Numerous cracks can develop on the fruit and this can be caused by wide fluctuations in the moisture content of the air.

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