Q. The recent column on tomatoes has inspired me to try growing them again. I tried many times in DHA, Karachi, and also in Malir but each time the plants were attacked by curly leaf virus. Is there some way of protecting tomatoes against this?

A. This nasty virus is carried by whiteflies. Spraying the plants with warm soapy water, garlic spray, chilli spray or a neem-based organic pesticide at the first sight of whiteflies is the best method of control. It is also important to keep the area around the tomato plants weed-free as some weeds host whiteflies, too.

Q. I have a 300 sq ft space on my house roof in Karachi. It receives plenty of direct sunlight. Which vegetables and flowers can be grown there, keeping in mind the local climate and temperatures?

All your gardening queries answered here

A. This may not be the reply you expected but first and foremost, you need to create both shade and wind protection. Otherwise, exposed as your rooftop is, few plants will survive. Shade and wind protection can be created from a combination of shade cloth and sturdy frames and it is essential that everything is firmly fixed in place; otherwise a strong wind can bring the whole lot tumbling down, possibly injuring someone in the process. Safety is paramount.

Once this is achieved, you should be able to grow a wide range of vegetables and flowers in pots/containers carefully selected to accommodate the roots of whatever it is you decide to cultivate. Please keep in mind that pots/containers full of soil and plants are very heavy, even more so when the soil is wet. Before putting them in place, it is advisable to consult with a construction engineer to find out if your rooftop is capable of supporting the weight without causing structural damage. Lots of people are creating wonderful rooftop gardens now and they are veritable private paradises within the city, but it is important to check feasibility and fine details before beginning to turn your dream into reality.

Q. I want to grow cherry blossoms in Karachi. Is this possible and, if so, where can I get the seed? If not, then please suggest a flowery alternative.

A. The Karachi climate is not suitable for cherry trees, but if it is gorgeous spring blossom you desire then invest in a Kachnar (Bauhinia) sapling. The orchid-like blossoms are stunning and they often begin to flower at just two years old; the flowers are edible. This small- to medium-sized tree should be available in local nurseries over the winter months.

Q. I want to grow potatoes in rooftop containers and would be grateful for advice. I haven’t attempted this before.

A. This is the perfect time to begin. Select pots/containers that are at least 12 inches in diameter and 24 inches deep if you want to plant just one potato per container or something like a large bucket or bin with a 40-litre capacity for four potato plants at once. Ensure that drainage holes in the base do not get blocked — laying broken pieces of clay plant pot, at angles, over the drainage holes is an easy way of doing this. Put about six inches of good quality soil mixed with well-rotted manure/organic compost into the pot/container. Then lay a potato (preferably one that is already sprouting) on top, with as many of the potato sprouts as possible facing upwards. Cover with approximately four inches more of soil/manure/compost mix and water. Keep the soil moist but not overly wet. Shoots should appear fairly quickly. Each time they do, cover them with a little more soil mix until the pot/container is almost full. Allow the plant/s to grow to maturity, flower and to naturally die back before digging up the crop (this will be about 60-80 days from planting). When watering, avoid getting the plant leaves wet as this can result in diseases such as blight.

Q. I recently bought a weeping willow from an Islamabad nursery but two days after I planted it, in a local park, its leaves began curling up and the stems turned yellow. There are also black spots on the leaves. What can I do to save it or should I take cuttings from it and try to root them in water to get a new tree?

A. Black spot is a common problem with weeping willows and its sudden appearance was probably encouraged when the sapling suffered transplant shock on being moved from its comfortable pot into the ground. Continue tending it, keep it weed-free and it should develop new leaves in the spring.

Q. I have two sharifa trees. One is about five to six years old and gave only two fruits three years ago. The other is two years old and had fruit on it when purchased six months ago. What should I do to encourage them to fruit and when is the fruiting season?

A. Sharifas (Annona reticulate or Custard apples) can be encouraged to fruit by training branches to grow downwards rather than upwards. This can, with care and with young, supple, branches only, be achieved by securely tying a weight towards the branch tip — a smallish weight at first, increasing the weight over a few weeks but stopping when branches are still at least three feet above the ground. Do not attempt to bend old branches as they may break. Plenty of water, from flowering through until harvesting, is essential. Sharifas generally fruit over the cooler months of the year.

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, EOS, November 11th, 2018