Monty Don shares one trick to making tomatoes grow bigger and tastier

Tomatoes are a favourite among gardeners due to their ease of cultivation, but they require more nutrients than most other plants. Gardening expert Monty Don from Gardener's World suggests that tomatoes will yield larger and tastier fruit if adequately supplied with potassium, an essential nutrient for fruit production.

The green-fingered guru also revealed how to create a homemade potassium fertiliser to give your crops a boost using just one common garden plant. Monty told the Express: "Potassium is what plants need to form good flowers and fruit, and fruiting flowers like tomatoes and gooseberries have quite a high potassium demand.

"You can boost that at this time of year and improve fruit production. One way of doing that is to go to a garden centre and buy liquid or granular fertiliser, but there's no need as you can also grow your own supply of potassium really easily through comfrey."

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Comfrey, a common garden weed recognised for its large hairy leaves, is rich in potassium and other nutrients needed by tomatoes, such as calcium.

Monty added: "Its main use to me in this garden is to provide the raw material for a liquid feed that's high in potassium." But he cautioned: "A word of warning about comfrey is that once it gets established it has deep roots and it's quite hard to get rid of. However, you shouldn't get rid of too much as it really is so useful."

How to make a homemade tomato fertiliser

You will need comfrey leaves, a large waterproof bucket with a lid, large stones to weigh on the bucket, plastic bottles (old milk bottles will do) and a watering can.

When gathering comfrey leaves, remember to wear gloves as they can irritate the skin. Once you've collected enough leaves, remove any flowers and stems, chop them up, and pack them tightly into a waterproof container.

Fill the container with water, seal it with a lid and find a safe spot for it in your garden. Gardening guru Monty Don advises: "The idea is to loosely fill a bucket or just put what leaves you've got, then put water in on top of that and leave it to brew for three weeks."

Don't forget to add a weight, like a stone, on top of the lid. While comfrey works wonders for tomatoes, its aroma during the breaking-down process is less than appealing. Monty Don said: "Then when it is properly made, it will form a black vile-smelling sludge, and I'm not exaggerating it smells disgusting... it's covered not to protect the brew but to protect us from its vile smell.

"After about three weeks, you'll notice the mixture transforming into a pungent brown liquid that's your cue that it's ready. Bottle it up in plastic containers and store in a cool, dark place."

When it's time to give your tomatoes a boost, dilute the concentrated fertiliser with water (one part comfrey liquid to ten parts water), adjusting the ratio based on the colour - the darker, the more diluted it needs to be. Then place it in a watering can and use it to feed your tomato plants, where you will help give your tomatoes a boost to get bigger, juicer and better quality fruit for your next harvest.