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Garden answers
Here are the answers to some commonly asked gardening questions. This section is constantly being updated.
If you are unable to find the answer here, then why not send me an e-mail
Houseplants
Q My aspidistra is looking very sick. It produces new leaves but very soon they go brown at the tips and then this spreads up the leaf. Why?
A Brown and crisp edges to aspidistra leaves is caused by the plants being stood in a very warm, dry atmosphere. The common name of cast iron plant came about because they grew very well in cold, dark parts of old Victorian houses. But they aren't very good plants for modern houses with central heating which produces a warm, dry environment.
Repotting isn't the solution as aspidistras prefer to be potbound. If you do decide to split the plant, make sure you repot the divisions into a pot only just big enough to take the roots.
Q Can you tell me why the leaves of my Christmas cactus have turned a reddish colour?
A There are a number of reasons why the leaves of Christmas cacti turn red.
The plant may have been overwatered - being a type of desert cacti they don't like to be waterlogged. Knock the plant out of its pot and check that the roots are still white and healthy. Remove any damaged or dead roots and some of the stagnant compost, and repot into a container only just big enough to take the resulting rootball.
It may have been placed in a position where it receives too much direct sunlight. Again, being a desert cacti it only needs diffuse light.
Last, it may be not have been fed enough. Feeding now will also help flower production.
Q Is it possible to grow an avocado from a stone?
A The avocado is not hardy in Britain - it comes from a tropical climate - so has to be grown as a houseplant. It will never fruit in this country but makes a useful foliage houseplant. Plants soon become tall and lanky if not pinched back regularly.
Position the plant in plenty of light - close to a south-facing window in winter and autumn, a west or north-facing one the rest of the time.
Pruning is best started as soon as the shoots are about 15-23cm (6-9in) high - you just take out the growing tip. Pruning and pinching out is best carried out from March to August.
Q What's wrong with my begonia plants? The leaves have brown marks on them.
A From your description, it could be sun burn.
Begonia leaves are very sensitive to strong light - they prefer a position in light shade - certainly out of strong, burning sunlight.
Sometimes small molecules of water settle on the leaf and then act like a magnifying glass when the sun is on them.
Check for any other symptoms like tiny black insects (thrips or tarsonemid mites) which might be damaging the leaves. If these are absent then it will definitely be the problem with the sun.
Q Why did my indoor plumbago drop all its leaves in winter?
A It's quite common for plumbago to shed its leaves in the winter. Just be careful about watering - don't drown the poor thing, but don't let the compost turn to dust either.
Plumbago should be pruned annually in late March/early April. The aim is to build up a framework of main stems to cover the area needed, and then to cut back all the side growths coming from this framework to a couple of inches long.
Q Any help please on looking after a dragon tree (dracaena)
A Dracaenas need average warmth - with a minimum winter temperature of 55F.
Plants need good, overall light - but not strong direct sunshine; an east or west-facing window would be ideal.
Keep the compost moist at all times; reduce watering in winter but don't let the compost dry out.
You should mist the leaves regularly to increase the humidity and stop the leaf ends turning brown.
Q I repotted some cyclamen plants I had kept from last year. They have good healthy leaves on but no flowers. Should I be feeding them and if so with what? They are indoors in my conservatory which faces west.
A The problem may lie in the repotting. Cyclamen - like other flowering houseplants - like to be potbound to encourage flowering. Only when the pot is full of roots will they start flowering.
Help encourage flowering by feeding fortnightly with a high potash liquid fertiliser - such as a tomato food or similar.
Q For the first time ever, I've managed to keep my Christmas poinsettias alive for the year by spraying regularly. They are fairly healthy with new leaves. How do I make the tops turn red?
A To encourage a poinsettia to turn its bracts red, you have to give it 14 hours of complete darkness every day for 8 weeks. It is essential that you don't give the plant any light at all during the 14 hours.
Q I am growing an indoor bamboo which came in a glass jar and which isn't doing that well. Can you give me any advice on growing it.
A I would be tempted to take it out of the glass and repot it into a pot of John Innes No 1 compost. The pot should be about 9cm (3.5in) wider than the diameter of the rootball/roots. The best time to do this is March to May.
These plants are almost hardy so don't molly coddle it.
Keep it in good light - on a west or east-facing windowsill for instance.
Keep it cool - don't let the temperature soar especially if your house is heated by central heating which will dry out the atmosphere.
Keep the air around the leaves humid - spray with tepid water daily or, better still, stand on a saucer filled with moist pebbles.
Q I have two banana plants. One is doing OK, but the second is having a hard time. It's name is Ensete ventricosum. I ordered it by mail from Louisiana. (I live in Oakland, California) It had two leaves when it arrived. The first two leaves were greenish with yellow/brown cracking at the edges, the emerging leaf was a healthy green. I thought that as the plant grew, I would have several healthy green leaves, and could cut the others off. It's only growing about one leaf a month, however, and the leaves are turning brownish yellow sooner than the poor plant can produce new leaves.
Do you have any advice? Maybe things will get better when the days ar longer? I am fertilizing it, and watering it frequently. I also wipe the leaves sometimes, I find some reddish stuff on the cloth after wiping them and it looks like there are tiny red bugs living there on the leaves.
A To be honest, bananas aren't the easiest of plants to keep looking attractive and growing well. The leaves naturally shred and the plant looks untidy.
I presume the plant is growing outside.
Light levels now are a bit too low for strong growth, but things will get better in spring. As a result of these low light levels the plant won't be growing much if at all, so feeding should stop - the plant can't use it so it just sits in the soil and builds up to toxic levels burning the roots.
Plants also need less water when not growing so try reducing the amount of water you're giving. Bananas don't like too much water.
Without seeing the patient it is difficult to make a diagnosis on the stuff on the leaves. It's possible that if it is bugs they are are masses of red spider mites which attack plants in dry conditions. Try using a general insecticide to try and get rid of them. But it could just be a natural bloom. Stop wiping the leaves, mist with tepid water if you want to try cleaning them up; if it is a natural bloom you may be harming the foliage.
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