Unwins Seeds

Growing tomatoes

Tomatoes have come on in leaps and bounds over the years and now we see multi-coloured tomatoes, attractively striped and spotted. They’ve been bred to withstand diseases, some you can grow outdoors and now there are grafted tomatoes, where the fruiting plants grow on robust roots for prolific growing.

Just read these helpful pointers to guide you in growing this popular and versatile salad vegetable.

Sowing tomatoes (indoor varieties – grow on single-stem cordons and outdoor varieties – bush-like growth)

Germination time 1 -1 ½ weeks

In late February to mid-March sow seeds singly into module trays or sow into a seed tray and prick out into 9cm pots when the seedlings are approx. 2in (5cm) high, and with 4 leaves.

You can them transplant them into grow bags, containers or prepared soil in the ground.

Planting tomatoes (indoor varieties – grow on single-stem cordons and outdoor varieties – bush-like growth)

Plant into pots, baskets or soil in the ground when you see the first flower form. Spreading black plastic over the soil surface and planting in slits made into the plastic will give tomatoes plants a head start. The roots will appreciate the increased soil warmth that the plastic allows.

Feeding Tomato Plants (indoor varieties – grow on single-stem cordons and outdoor varieties – bush-like growth)

Add a general purpose fertiliser to soil before planting, and if digging over the soil in winter pre-planting, add bulky compost to increase the soil fertility.

For container-grown tomatoes, feed regularly with tomato feed.

Feed little and often – this will ensure the tomato fruit ripen well and do not split- an indicator of sporadic yet deluge-like feeding.

Watering Tomato Plants (indoor varieties – grow on single-stem cordons and outdoor varieties – bush-like growth)

Like feeding tomatoes, watering too needs to be a set quantity and often, rather than sporadically. Tomatoes are thirsty plants and for healthy growth need water regularly and evenly. Misting plants, particularly indoor types, will keep humidity up, keep red spider mite at bay, and allow a more favourable growing environment for the plants.

You can water the floor of the greenhouse to encourage rising humidity.

Similarly water outdoor tomatoes regularly and evenly. Be aware that a rain-shower will not be sufficient to substitute a watering.


If young seedlings or young plants have rotted, more or often than not it’s down to over-watering.

Prevent this from happening;

  • When young, water from above when soil feels dry until roots are emerging from the bottom of the pot.
  • Never stand pots in water for a length of time. Roots need to breathe and get sufficient oxygen; if you keep them standing in water they drown.

A good tip for established plants is to stand them in a tray of water overnight, if the soil is dry. In the morning tip out the excess water from the tray. Only ‘flood’ the tray again when soil surface feels dry to the finger tip. Again, make sure you re-visit after a few hours or overnight to tip out excess water.


For germinating seeds ensure an ambient temperature of 18C (64F). As seedlings/ young plants grow ventilation is key and if growing indoors make sure plants are shaded to lessen the burning effects of direct sunlight of 25+C (77F).

How to prune

Indoor cordon-types

Tie the main stem loosely with string or twine to a central cane. As the young plants grow side shoots called suckers will grow out of where the leaf stalks join the stem. Pinch these out once they reach 3cm (1in).

Once the plants are 1.2m (4ft) tall, remove leaves below the first flower stem. (This is called the ‘truss’ and the flowers stems turn into the ‘tomato vines’. Remove yellowing leaves as the season goes on, but look to remove only about a half of the yellowing leaves.

When the plants reach the top of the roof or you’ve counted around seven trusses. Pinch out the tip at 2 leaves above the top truss.

Outdoor bush-types

These tomatoes do not need as much pruning , and you can enjoy the fruits without any truss- counting, stem pinching etc. Although they are easier to grow in this respect, they are needier in other respects and you may need to be vigilant in spotting more pest and disease damage or nutrient deficiencies.

Harvesting and Storing Tomatoes

Harvest fruits when they are ripe and deep red, but still possess firmness to grip. Twist them off so they break off at the swelling of the old flower stalk.

For the glut of green tomatoes at the end of the season, harvest and place with other ripe fruit to encourage the hormone ethylene to do its work in ripening fruit quickly.

Alternatively pick and use the green tomatoes for chutney, curry and other recipes that take advantage of the tang of unripe tomatoes.

Tomatoes stay fresh for a week when refridgerated.

You can pulp tomatoes and freeze as a passata for future use.

Best Varieties of Tomatoes

Artisan Tiger Stripes


San Marzano


Pests and Diseases of Tomatoes

Blossom end rot, Split fruit, Dry set, Root rot, Leaf yellowing, Mosaic virus

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