Basil is one of the most popular potted herbs, ideal on a kitchen windowsill to tear off as required and add to tomato and mozzarella salads, soups, sauces and home-made pesto.

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However, the reality can be different. Within a few weeks the supermarket plant has often become leggy, yellow and a few steps from death. So, what did you do wrong?

So often basil wilts and dies within days. (Hannah Stephenson/PA)
So often basil wilts and dies within days (Hannah Stephenson/PA)

“The chances are it was simply a case of the pot being too small – the shops put a lot of plants into one pot to make them look bushier and more attractive. But very soon they outgrow this home and need a bigger pot,” says George Williams, CEO of plant care advice app SmartPlant.

“This can easily be solved by removing individual plants by the roots, and replanting them into a bigger pot.”

Here’s what to do:

Repotting basil

Repotting basil. (SmartPlant/PA)
Repotting basil (SmartPlant/PA)

Fill the base of your new basil pots, which need good drainage holes, with multipurpose compost. One large supermarket-bought basil pot should make around five smaller plants. Split the existing healthy plant gently into sections, without touching the stem or the leaf, teasing the roots gently apart.

Plant them in the compost, packing compost around the plants to fill the pot, making sure the plants are at the same height that they were in the original pot, and water from below.

Choose a sunny spot

Basil likes sunlight. (Thinkstock/PA)
Basil likes sunlight. (Thinkstock/PA)

Find a space with lots of sun, as ideally basil needs 10-12 hours of light a day.  Choose a south-facing window, or whichever one gets the most natural light. At sundown, a fluorescent grow light can be used to top-up the number of sunlight hours.

[Read more: How to grow herbs you can’t find in the supermarket]

Be waterwise

Water but don't over-water. (Thinkstock/PA)
Water but don’t over-water (Thinkstock/PA)

Basil likes moisture too – but not too much. Its soil should be kept moist, but not soggy, or its roots may rot. Make sure your  indoor container has good drainage.

Fertilising your basil plants every few weeks will keep them strong and healthy. Any household fertiliser will do, but use it at half the recommended strength.

Regularly check your plant for small insects. You can’t blame them for choosing the ‘Royal Herb’ as their palace, but make sure you wash them off – they aren’t good for your plant or your plate.

Keep harvesting

Pick leaves from the top. (Thinkstock/PA)
Pick leaves from the top (Thinkstock/PA)

The beauty of this delicious herb is that harvesting its leaves encourages further growth, but only if you leave a section of leaves remaining each time. Pick leaves from the top, pinching just above a leaf pair, which will also encourage further growth.

Remove any flowers, which will dull the flavour of the leaves.

If you’ve got more basil than you know what to do with, you can either freeze it in ice, or dry it out and store it in containers.