Growing Tomatoes: Greenhouse Growing Guide

Many acres of greenhouse are devoted to the cultivation of tomatoes, and they may also be raised successfully from seed in frames. A tomato house should never have a temperature of more than 70° F. (21° C.) in the daytime, or less than 50° F. (10° C.) at night, and it should always be well ventilated, particularly in midsummer, so that the growth does not become too lush and soft.


Sow tomato seeds in the greenhouse any time between February and late May. Later sowing produces a crop that needs very little artificial heat, while a February sowing will yield fruit from early July till October, leaving the greenhouse free for bulbs in early spring and chrysanthemums in the autumn.

Fill a seed box measuring 14 by 8-1/2 in. with John Innes seed compost or Eclipse No-Soil compost. Press down and level the compost before sowing the seeds 2 in. apart. Push each seed into the soil with a pencil and cover with ¼ in. of the compost or sterile sand. Again press the soil down gently with a board to within ½ in. of the top of the box. Water from a can with a fine rose, using rain-water if possible, but do not allow the soil to become sodden.

Cover each box with a piece of glass and put a sheet of newspaper on top, removing these each morning to wipe the condensed moisture from the glass. When germination takes place, in about seven days, remove the glass and paper altogether and place the boxes as near as possible to the glass roof of the greenhouse. The temperature of the house throughout this stage should be maintained at about 55° F. (13° C).


Seeds raised in frames should be sown early in April. Fill 3-in. pots with John Innes seed compost or Eclipse No-Soil compost, and sow three seeds 1/2 in. apart and 1/2 in. deep in the centre of each pot. Place the pots in the frame, and when the seedlings appear, thin them down to one to each pot.

They should then be left in the frame until the end of May, when they should be ready for planting out in the garden.


After about 28 days the seedlings that are in boxes in the greenhouse should be about 1-½ in. high, with two pairs of true leaves. Each seedling should then be potted off into a 3-in. pot, using John lanes potting compost No. 1. Always handle the plants by the leaves, never by the stems.

At the beginning of May plants that are to mature out-of-doors should be placed, in their pots, in cold frames to harden. By the third week of May the glass of the frames may be removed, and the plants should be ready for planting out in the garden at the end of May or early in June.

Plants that are to continue growing in the greenhouse may either be planted out in the border, potted on into larger pots or boxes, or cultivated in rings on beds of aggregate.


The ideal soil for tomatoes grown in the border of the greenhouse is a friable, well-drained, but firm, sandy loam. Dig in 4 oz. of fish manure per sq. yd., and spread l lb. of lime per 100 sq. yds. on the surface of the soil. To improve aeration in soil that is heavy, or which has held tomatoes for several years, dig straw into the ground, or use a bucketful of coarse peat per sq. yd.

When the young plants are about 5 or 6 in. high, turn them out of their 3-in. pots, carefully keeping the ball of soil intact and removing only the crock. Most varieties can be planted 15 in. apart in rows that are alternately 1 ft. 9 in. and 2 ft. 3 in. apart. With proper treatment each plant should yield an average crop of 6 to 8 lb.

Water the plants in well immediately after planting. Thereafter, a good soaking once or twice a week will generally be sufficient. It is difficult to lay down hard and fast rules, however, and the gardener should be guided by the appearance of his plants as well as by atmospheric conditions. If the leaves flag, it is a sign that water is needed; a light sprinkling of water over the leaves is also beneficial.

Do not be tempted to over-feed with manure during the growing season, as this may result in the dropping of the flowers, watery and insipid flavour, and disease because the plant is soft. Top dressings of peat or straw may be given as a mulch, and a fish fertilizer with a 10 per cent potash content may be applied in July, August and September, using about 2 oz. per sq. yd. Watering with Liquinure (Tomato Special) is also an excellent method of feeding tomatoes in summer; use once a fortnight, following the instructions on the bottle.


Plants that are to mature in boxes or pots should be grown for about three weeks in their 3-in. pots and then transferred to 5-in. pots for a similar period. Meanwhile, fill 10-in. pots or boxes with a compost of two parts good soil to one part peat, filling to within about 4 in. of the top, so that top dressings can be added later. Leave the compost to warm for some time before planting, and then dig a hole large enough to hold intact the ball of soil from the smaller pot, so that the root system is disturbed as little as possible when the plant is moved.

Give a top dressing of 2 to 4 in. of John Innes potting compost No. 2 when several trusses of fruit have set. Another dressing may be necessary six weeks later; water well after each dressing to settle the soil. Pot plants require more watering and manuring than plants in the border, and it will usually be necessary to water every day, adding a suitable liquid feed to the water twice a week.


This method indicates the growing of tomato plants in open-ended pots, which stand on beds of moist aggregate. The plants form their first root system in the pots, where they obtain their food, and a secondary root system in the aggregate, from which they receive moisture. Ring culture is labour saving, and has the added advantages of promoting steady growth, earlier cropping and greater freedom from soil diseases.

To make a bed of aggregate, dig a trough or excavate the floor of the greenhouse to a depth of 6 in. Line the sides of the excavation with slate or polythene to prevent the soil from washing in. In the case of clay soil, which does not drain freely, slope each side of the base of the excavation towards the centre, and give the trough a very slight overall incline. Cover the base with a polythene sheet, and place drain-pipes down the centre, leading to a rubble-filled hole outside the greenhouse. Then fill the trough with aggregate.

The best aggregate is weathered boiler ash, which can be kept moist. Alternatively, use fine weathered clinker or a mixture of three parts 1/2-in. gravel and one part coarse grade vermiculite.

Wash the aggregate with a 2 per cent formalin solution each year, and close the greenhouse for several days. It should then be ventilated until all the fumes have disappeared.

For a double row of tomato plants, make a bed 3 ft. wide, or for a single row, 1 ft. wide, pressing down the aggregate well and then soaking it with water.

Make bottomless pots for the tomato plants from rings of roofing felt or lino 9 in. deep and 9 in. in diameter. The simplest nutrient compost is the John Innes potting compost No. 3, or Eclipse No-Soil compost, a bushel of which will fill five 9-in. pots. Good results can also be obtained from three parts heavy loam and one part peat (both by bulk), adding 12 oz. John Innes base fertilizer and 4 oz. ground chalk.

At the end of April or in May, stand each ring on a slate, and half fill it with compost, pressing this fairly firm with a piece of wood. Set a plant, which should be showing its first truss of flowers, in the ring, and pack compost round it to within l in. of the top of the ring. Place the pots on the aggregate, leaving 1-1/2 ft. between each; pack a little aggregate between them.

Keep the aggregate moist by frequent watering, but do not flood it, for the plants should receive only a little water until the first flowers have set, so that roots develop downward into the aggregate before growing in the compost. Water the pots only when the ball of soil dries out, and if they are splashed from the daily watering of the aggregate, it is not necessary to water them separately.

Start feeding with a liquid fertilizer when the first truss of flowers has set and the fruit is beginning to swell.

Frequent feeding gives the best results, and should be confined entirely to the pots. Give about one pint per plant every third or fourth day, and water the aggregate afterwards.


Whichever method is used for growing greenhouse tomatoes, all side shoots should be pinched out immediately they appear, and dense foliage may be thinned to allow air and sunlight to reach the fruit.

Avoid any ruthless cutting away of the leaves, though any yellowing leaves may be removed.

Stop each plant by pinching out the growing point when it has produced nine or ten trusses of flowers.

All tomato plants need support. Bamboo canes can be used, or lengths of string can be attached to overhead wires strung tightly from one end of the greenhouse to the other, about 6 ft. from the ground. Tie the other end of each string to the base of a plant, or to a short bamboo cane driven in near its base, and twist the string round the plant as it grows and needs support.


The following varieties of tomato are recommended for cultivation under glass:

All Clear, a good cropper, fairly resistant to mildew.

E.S.5, a tall, heavy cropping variety, with fruit of excellent quality.

Eurocross, a hybrid which is resistant to tomato mould disease; a heavy early cropper.

Market King, a heavy cropper, good flavour.

Syston Cross, a free-setting, short-jointed variety, immune from tomato mould disease; easy to grow.

16. February 2012 by Dave Pinkney
Categories: Featured Articles, Garden Management, Gardening Calendar | Tags: , , , | Comments Off on Growing Tomatoes: Greenhouse Growing Guide


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