FAQ - Growing Tomatoes

How to Grow Tomatoes

Tomatoes are very rewarding to cultivate and it doesn’t have to be hard, but if you find yourself struggling here is a guide to the most frequently asked questions.

How Do I Cultivate Tomatoes?

Tomatoes make an excellent plant for cultivating either in a growbag or pot provided a few simple steps are followed, in particular getting your watering regime correct. You can find a full step by step guide for cultivating tomatoes here.

How do I cultivate tomatoes from seed?

To cultivate tomatoes from seed you need to fill a seed tray with any multi-purpose compost. Sow the seeds in furrows, cover and water them. They now need to be kept in a heated propagator or on a warm windowsill at a temperature of 18 degrees and should be ready to prick out in 4 weeks. You can find a detailed Tomato cultivating guide and video here.

When should I sow my tomato seeds?

If you are growing your tomatoes in a heated greenhouse or are using a heated propagator with optional grow lights you can sow them in January to February. When doing this you need to ensure that the soil is kept at around 18oc. If you plan to sow you seeds outside you will need to wait until late March or early April.

What varieties to use?

Our Gardening Angel Paul recommends the following 4 varieties of tomato;

1) Beefsteak Tomatoes: Country Taste

2) Cherry Tomatoes: Sungold (orange), Rosada (baby plum)

3) Standard Tomatoes: Cristal

4) Plum Tomatoes: Olivade, San Marzano

When should I plant my tomatoes?

It should take around 60 days for your seedlings to reach the point where they can be pricked out. At this point they should be around 3cm tall and will need to be transferred to individual 3 inch pots. Once your tomatoes are 15-20cm they will be ready to be transferred to their final growing pot.

Do I need to support my tomatoes?

Bush (determinate) tomatoes will grow to approximately  1 meter and may require a certain amount of staking. Vining (indeterminate) tomatoes can grow to 9 meters and will need substantial support. Take a look at our support frames.

quadgrow support frame

Do I need to prune tomatoes?

You will need to remove the side shoots of certain varieties, which involves removing the new shoots growing between the leaf and stem ensuring that all the plants energy goes into growing its main stem. Once the plant has reached a desired height you will need to remove the growing tip. You can find videos on how to do this here.

Can I cultivate tomatoes outside?

Yes you can cultivate tomatoes outside, however you will have to be aware of issues which are largely absent when cultivating in a greenhouse. Tomatoes cultivated outside will need protecting from the elements and will need close monitoring for under/over watering. Do not plant tomatoes outside until night temperatures are above 10 degrees.  Tomatoes will be slow to ripen outside as the will need heat and light.

Can I cultivate tomatoes in a conservatory?

A conservatory is the ideal place to cultivate tomatoes, particularly if you don’t have access to a greenhouse as you can easily control the growing conditions of your plant. The main issue you could have is with erratic watering as this will stress the plant and could then lead to fungal diseases. Self-watering kits such as the Quadgrow will eliminate this problem.  

quadgrow self-watering planter

What pests do I have to watch out for?

Tomatoes suffer from much the same pests as any other plant, however the most common would be aphids. Aphids will gather around new shoots or young plant leaves and you will commonly see a curling of the leaf as the aphid sucks on the sap. They can be controlled with a pesticide or by introducing a natural predator such as ladybirds.

What is blossom end rot?

Blossom end rot is a dark circular patch around 1cm in diameter at the base of the fruit. This is not caused by a pest or disease, instead it is due to a lack of calcium usually due to a poor watering regime.

How can I prevent blossom end rot?

There is unlikely to be a lack of calcium in the soil, however a good water supply is needed to transport the calcium to where it is needed in the fruit. Fruit which has developed blossom end rot cannot be saved, however it is a good indicator that the watering regime needs to be improved. The soil should be constantly moist throughout the growing season, if this is not possible a self-watering planter will solve the problem.  

What is tomato blight?

Tomato Blight is a common problem among outdoor grown tomatoes and is a fungus like organism which spreads rapidly through a plant during wet weather periods. Blight is characterised by a rapidly spreading rot through the leaves and stem, green fruit will also turn brown and mature fruit will decay rapidly.

How can I prevent tomato blight?

Infected plants should be removed and either buried or taken away for green waste collection, this will help prevent the spread of any infection. For outdoor plants you can spray your plants with protective sprays when wet weather is forecast, however in very wet weather this will only slow the spread of the disease and not prevent it. For indoor plants as long as you follow a good watering schedule and do not over water your plants they should not contract the disease.

Why are my tomato plant leaves curled?

There are 2 main reasons for leaf curl, the first is Aphid in which case you will see clusters of this pest gathered on the underside of the leaves. This pest sucks the sap from the leaves  giving them the appearance of shrivelling up. Alternatively it could be a reaction to environmental stress’ such as temperature or watering, in this case the plant should recover within a week of this stress finishing.

Why do my tomato plants have spots on them?

The most common reason for spots appearing on your leaves is a fungal or bacterial attack however it could also be and early indicator of blight. Your plants become susceptible to fungal attacks when they are stressed and the most common reason for stress is watering issues. Treating the plant with a fungicide will help control the fungus however if it has spread to the majority of the plant you are best removing it from the growing are to prevent any spread.

What is grey mould?

Grey Mould is the common name for Botrytis, similar to tomatoes it presents itself as a grey fuzzy mould on a plant which is stressed, in very bad infestations the whole plant can shrivel and die rapidly.

How can I stop Botrytis?

There is currently no cure for botrytis available to amateur growers, if a plant develops the signs of an infection it should be taken away from other plants and either buried or taken away for green waste collection, it should not be used for home composting.

How tall should my tomato plants get?

Tomatoes will continue growing until they are prevented from growing by the weather or a lack of food and water. In reality the plants are allowed to grow to a manageable height at which point the growing tip is pinched out forcing the plant to put on side growth instead of height. Our Gardening Angel Paul regularly grows tomatoes in a Vivigrow planter which eventually grow to 9 meters before he pinches them out.

Vivigrow Planter

What is ‘pinching-out tomatoes’?

Pinching out is where you remove the growing tip of your tomato plant once it has reached its desired height. This will force the plant to throw out side growth instead of putting on more height and it is this side growth where truss’ are formed. To ‘pinch-out’ the tip you will need to leave 2 leaves above the last flowering truss and cleanly pinch the tip away from the stem.

What is a tomato truss?

A Tomato truss is simply the stem on which the yellow flowers develop, these will later fall off and develop into fruit once they have been pollinated.

How do I harvest tomatoes?

Pick tomatoes as soon as they are ripe (this will encourage the plant to produce more) make sure you leave the stalk (calyx) on the tomato for a longer lasting fruit. The ripening process can be speeded up by using a ripening cover.

ripening cover

How many tomatoes can I expect to harvest?

The amount of tomatoes you can expect is dependent on a number of factors, the variety of tomato you chose will affect the outcome greatly as will the environment in which it is grown. Typically a plant will keep producing fruit until something changes to stop them producing fruit (i.e. food, water or suitable weather) If you are growing in a greenhouse you can control these factors more precisely and extend the growing season. Cherry type tomatoes will produce many smaller tomatoes wereas beefsteaks will produce fewer larger fruit.

How can I make green tomatoes turn red?

Contrary to popular belief tomatoes do not require a large amount of light to ripen, instead they require heat. If you are growing tomatoes indoors or in a heated greenhouse you should not have a problem ripening your fruit. If your plants are growing outside or in a unheated greenhouse you may notice them start to slow down as the season progress’ in this case using a ripening cover will insulate the plant and continue the ripening process.