Q. For many decades, in my village in Murree district, people have been constructing septic tanks that have messed up land, and natural water springs. Could you please suggest some plants/trees that could be grown around these septic tanks to mitigate their effects?

A. From personal experience of the area, I believe you are talking about soak pits not septic tanks, as there is an important difference. A soak pit is a fairly old-fashioned method of dealing with household wastewater and sewage. It is an underground pit, filled with stones which filter solids that get slowly digested by bacteria. Excess water eventually seeps out into the surrounding soil. Soak pit water is not safe for irrigating edible crops of any kind.

On the other hand, septic tanks are of an enclosed design, including filter systems, and the resultant greywater can be used for irrigation of some crops, as long as the connected household does not use large volumes of detergents. Detergents kill bacteria that are necessary for septic tanks and soak pits to work efficiently. The majority of soak pits in the Murree area are quite old, and increasingly abused by household detergents. These should have been either replaced or upgraded to septic tanks years ago.

Because of the aforementioned reasons, many soak pits no longer work, and the highly contaminated water seeping from them pollutes the adjacent soil, seeps into the groundwater system, and eventually contaminates valuable drinking water springs too. To ease and hopefully prevent soak pit seepage at my property in the area, I planted weeping willow trees, chinar-maple, and poplar, at a distance of 3-4 metres from the soak pit boundary. Once established, these thirsty trees can be pollarded to control their height. The cut trunks/branches are used as animal fodder or fuelwood, and they quickly regrow.

All your gardening queries answered here

Q. We have a six-year-old guava tree in Tarnol, Rawalpindi. It fruits well but the guavas are not sweet even when ripe. Also, there is caterpillar infestation in them, as soon as they begin yellowing. The caterpillar issue was less this year, but the taste remains the same. We do not fertilise it but we do use pesticide. Please advise. 

A. Guava trees need rich, well-draining soil and should be fed, preferably with fully decomposed, organic, animal manure, every 3-4 months to achieve strong growth, and to maximise fruiting potential. Guavas also need regular and heavy irrigation, right from blossoming through until the harvest of fruit is complete. The sweetness of the guavas varies from variety to variety so, presumably, you are growing a variety of low sweetness, and there is nothing you can do to alter this. Caterpillar infestation is actually the larvae of fruit fly, a common problem with guavas, and one that has been discussed here in the past.

Q. The office gardener gifted me a guava plant two years ago, but it has not grown very well. What can I do to encourage its growth and help it to bear fruit?

A. Please study the answer to the precious question.

Q. What kind of growing conditions are required for a kurry patta plant? I have tried growing them in pots in Karachi. Despite taking good care of them daily, they always die.

A. Kurry patta plants/trees require a nutrient-rich, well-draining soil/compost, and lots of direct sunshine. They also need quite a lot of water, say once a week in winter, and at least every other day during summer. In a heat wave, daily evening watering is ideal.

Q. What is leaf mould and can it be made at home?

A. Leaf mould is an incredibly nutrient-rich compost, best mixed with sweet earth before being used to grow plants in. This excellent mulching material is simple and reasonably fast to make at home. Fill either a large-sized bin with a fitted lid or a large, black-coloured, garbage bag with packed-down fallen leaves, collected from deciduous — not evergreen — trees and shrubs. Close the lid of the bin or tie up the bag. After a month, take a look inside the bin/bag which should now contain a crumbly, dark brown, soil-like substance, which is pure leaf mould.

Q. Can rhododendrons be grown in Karachi?

A. No, because neither the climate, nor the soil is suitable for these gorgeous flowering shrubs. They can only be cultivated in the mountainous north of the country.

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, February 27th, 2022