Dr Christopher Teh, soil biologist and senior lecturer at Universiti Putra Malaysia answers gardening questions in the gardening column, Ready, Set, Grow!, which is brought to you by social enterprise Eats, Shoots & Roots. Go to questions.eatsshootsandroots.com to send in your queries.

I grow edible plants like herbs and vegetables in little pots on the balcony and near windows with plenty of sun. I notice that they don’t grow as lush as ‘landed’ plants. The leaves are smaller and not as green. Can you suggest a natural and safe fertiliser to use or any other eco- and health-friendly measures?

As a general rule, the larger the pot, the better. Larger pots give more room for your plant roots to grow, and with larger roots there is more plant growth. Smaller pots also encourage root coiling, a condition that distorts the roots.

Smaller pots also dry out faster than larger pots. This is generally why landed plants do better than potted plants. Smaller pots also contain less soil, which in turn may not contain sufficient nutrients for your plants.

Generally, you should use a pot with a diameter of at least 20cm and a depth of 15cm for small herbs and vegetables.

A natural and safe fertiliser I recommend is compost or mulch. (See “How To” column on making your own compost.)

How do I deal with mosquito larvae in the water when growing edible plants?

You have two options. You can install an appropriately sized aquarium air pump to keep the water moving. Female mosquitoes lay their eggs on the surface of stagnant water, so when the air pump blows bubbles into the water that keep the water moving, it prevents the mosquitoes from laying their eggs.

The second option is to rear fish in the water. They will eat the eggs, pupae and larvae of the mosquitoes. Koi, goldfish, betta fish, and guppies are good choices. Koi, of course, are large fish so that would be suitable only if your pond is large. Except for koi, feed the smaller fish less than usual to encourage them to eat the pests.

A suitable companion plant for tomatoes is the cucumber plant. Photo: Filepic

What plants can I grow that are companion plants?

There are too many suitable combinations of plants that can be grown together to list here. Without knowing which plants you are growing, I can only suggest that you search the Internet for a list of companion plants.

For instance, companion plants for tomatoes are onions, cucumbers, and asparagus, whereas companion plants for melon are okra and corn.