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Tomato Sowing and Growing Guide

Published: 27th April 2023

Tomato Growing Guide


Tomatoes are a more flexible and faster growing crop compared with peppers and can be sown from mid-March until the end of May. Early sowings will have to be grown in an unheated greenhouse but later sowings from mid-April onwards can be planted outdoors. Sowings from mid-May will also benefit from being in an unheated greenhouse as fruit will not start to ripen until late-August and to maximise crops it makes sense to keep the plants growing inside until the end of October.


A kitchen windowsill or a heated propagator is perfect for germination. You can use either a seed tray (with or without grids), or a few small pots – filled with a seedling specific compost. Make sure you moisten the compost before planting your seeds. Plant your seeds evenly apart from each other and sprinkle with a dusting of compost on top. Cover the seeds with a plastic bag if they are on a windowsill – this will keep the conditions warm and moist. If your seeds are in a heated propagator this won’t be necessary.

Tomatoes need to be kept very warm in the germination period. A temperature between 18-20 degrees Celsius is optimum.


Prepare to transplant your seedlings after about 2-3 weeks. Your seedlings should have 1 true leaf on them before you consider moving over to pots. 9cm pots are perfect for tomato seedlings, and they can stay in these for up to 4 weeks. Your tomatoes will still not withstand being outside at this point and will need to be kept inside on either a windowsill, in a conservatory or moved into a greenhouse/cold frame. Plants should not be moved outside into a non-heated greenhouse/cold frame before the mid-end of April. Tomatoes have no frost tolerance and will not survive in a non-heated greenhouse or a cold frame if there were a cold snap.


Once your tomatoes start to outgrow the smaller 9cm pots, you can move them into their final pot/grow bag/polytunnel.

  1. For indeterminate/cordon types plants can be moved into grow bags or soil beds or large pots with a minimum soil volume of 20 Litres. Train the plants up a bamboo cane or vertical string and remove side shoots which form in the axils of the leaves to ensure a tidy and disease-free plant. Ensure regular watering and feeding with a liquid fertilizer of your choice and avoid blossom end rot by ensuring plants do not dry out and air movement within the greenhouse is adequate to encourage transpiration from the leaves.
  2. For outdoor growing, plant from late May onwards when the date for the last frost has passed but remember to cover plants with horticultural fleece if a frost is forecast. Varieties like ‘Cocktail Crush’ will need a stake to support their growth, or a proprietary support structure can be used like:
  3. For bush varieties like ‘Veranda Red’ sow in mid-April and transplant into a large patio pot of around 10 Litres (a 5 Litre pot is also possible but watering will need to be more frequent) and place in a sunny and sheltered location. Feed and water regularly.


Tomatoes should be harvested when the fruit colour is fully developed i.e. red, yellow or orange. Don’t allow fruits to over-ripen on the plants as they can become infected with fungal diseases which can then attack the rest of the plant.

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