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Feeding tomato plant


Tomatoes are one of the most popular vegetables to grow, and if you want to pick the biggest, tastiest crop it’s essential to feed your plants.  The nutrients in compost or a growing bag will last for only four to six weeks. And even controlled-release fertilisers have a lower level of potassium – essential for fruit development – than tomato feeds, and will be running low by the time tomatoes are ripening.  Using a good liquid feed will give you sweet, ripe tomatoes for longer than controlled-release fertiliser alone, so we set out to see which of the currently available products will do the best job. Tomato feeds are also great for feeding pots of flowering patio plants, such as petunias and begonias.

When to feed tomato plants

Adding a controlled-release fertiliser to your compost at planting time will provide your plants with the nitrogen, phosphorus and potassium (NPK) they need for healthy growth, but they may well be running low by the time your tomatoes start to ripen. If you haven’t added a controlled-release fertiliser, you should start giving your tomatoes a liquid feed once the first truss of fruit has formed.

How often should you feed tomato plants?

Most products need to be applied at least once a week, with the frequency sometimes increasing once the second truss of fruits develops; check the dilution and frequency on the product label.

Is tomato feed good for all plants?

Tomato feeds aren’t just for tomatoes; most have more potassium in relation to the nitrogen and phosphorus, which helps to promote flowering and fruiting. You can therefore use a tomato feed  on any container-grown plants that produce lots of flowers or fruits, such as fuchsias, clematis, aubergines, cucumbers, peppers, courgettes and chillies.

How we test tomato feeds

We selected eight widely available tomato feeds to test, plus one specialised compost that doesn’t require feeding. In mid-April we potted up tomato ‘Shirley’ plants in a Best Buy peat-free compost to provide three plants per feed treatment, then planted these into their final 10L pots in mid-May using the same compost.

For the specialist compost on test, we potted up tomato plants into 10L pots of this compost. We began feeding our tomatoes in mid-June at the rates described on each product. The plants in the specialist compost were given only water.

We grew our tomatoes as cordons in an unheated polytunnel, stopping the plants by pinching out the growing tip after six trusses of fruit had formed. We rated the vigour of the plants, and the quality and yield of fruits for each feed. We also rated each product for ease of use.