Q. I bought a lemon plant about a month ago. It flowers perfectly but the fruit detaches itself very early. I have also noticed some black and yellow, active caterpillars on its leaves. I don’t want to spray pesticides and need a companion plant for it. I believe that guava is the one. The issue is that I have my plants in a gallery, so could you tell me of some small companion plants which are suitable. Should a companion plant be in the same pot as the plant it is a companion for? I reside in Garden East, Karachi.

A. Lemon trees shed immature fruit for a number of reasons, the most common ones being incorrect watering practice and lack of nitrogen in the soil. Over-watering and insufficient water both cause fruit to drop, so it is important to strike a balance: never allow the soil to completely dry out before watering and, when you do water, do not flood the soil. Waterlogged soil can also cause fungal diseases and root rot ... watering lightly and often is the best way. Nitrogen levels in the soil can be increased / maintained through regular additions of organic humus / compost, or you can grow members of the ‘legume’ family of plants (peas, beans, clover, alfalfa, etc) in the same pot as these enrich the soil, via their root systems, with much needed nitrogen.

Guava trees are, as you mentioned, good companions for lemons, but as you are restricted for space, you may like to grow one or more of the following in the same pot as the lemon tree (depending on room): Marigolds (not Calendulas), tagete, nasturtiums, petunias, borage, lemon balm, dill, thyme or parsley, all of which deter pests. The caterpillar problem can, as the tree is small, be solved by picking off the caterpillars / sponging off clusters of eggs with warm, soapy water. Good that you are growing organic. Keep it up!

Learn how to keep your plants as bright and sunny as the weather with these summer gardening ideas

Q. It is said that sewage water is the best fertiliser for plants. Your opinion is requested, please.

A. Sewage water requires various chemical treatments before it is safe to use for irrigation purposes but, sadly, this rarely happens here and tests (carried out by environmental agencies and others) have shown sewage water to be highly contaminated with toxic substances. Under existing conditions here, I do not recommend its use. Installing a sewage treatment facility solely for home use is, in our climate, prohibitively expensive.

Q. The usual linguistic framework we operate with mali, nursery, seed outlets, etc, is in Urdu whereas in your articles you only mention English names. It’s been a constant struggle to look for equivalent Urdu names or the nicknames with which they are available in the local context. Kindly add the Urdu names of every plant and technical entry you make. This would save us from confusion.

A. The problem is that whilst indigenous plant species do have Urdu or names in other local languages / dialects, few of the introduced species — these dominating the current flower, vegetable and herb scene — have names aside from their actual botanical names in Latin, or ‘common’ names in English. I do try to include Urdu names when possible, but even Urdu names are not understood by everyone. It is not possible to list names in Urdu, Punjabi, Pashtu, Seraki, etc, each time an indigenous species is mentioned as space is limited. The same applies to ‘technical’ words, many of which do not have even an Urdu equivalent. Whilst commiserating with your predicament, please do bear in mind that this is an English language publication in which English language standards are expected to be maintained.

Q. You have been advocating recycled household (grey) water for gardening use. The water after washing used crockery or taking a bath becomes a mixture of detergents, soaps, fats, etc. How can such water be used or made safe for gardening use. Please explain in simple terms.

A. A column dedicated to this subject is scheduled to appear next month.

Q. In winter my rooftop garden does well and produces tomatoes, salad, chillies, bitter gourd, grapes, strawberries, etc, but now all salad and tomato plants are dying in the heat. Can you guide me as to what vegetables can be grown in pots / crates in summer? There is shade for all the plants as well as five hours of sunlight each day.

A. Five hours of direct sunlight, in summer heat, is too much for some plants, especially as heat is intensified on rooftops. Salad plants will need shade all the time, as will other tender species. For what to plant and when, please consult the suggestions given on the first Sunday of each month and select from those.

Q. About one-and-a-half year ago, I planted an African tulip tree. It has grown extensively since then and produced beautiful orange flowers. I’ve been wondering if it’s possible to grow a Jacaranda tree too as it belongs to the same family. I live in Karachi and my garden is west open.

A. Congratulations on your African tulip tree. Jacaranda rarely does well in Karachi, I am sorry to say, but maybe you can give it a try and hope for the best.

Please continue sending your gardening queries to zahrahnasir@hotmail.com. Remember to include your location. The writer does not respond directly by email. Emails with attachments will not be opened.

Published in Dawn, Sunday Magazine, June 26th, 2016