Ask Adam: part five

Your questions answered

We recently invited you to submit your gardening questions for Adam Pasco, editor of Gardeners' World Magazine. View Adam's fifth set of answers, below.

Every two weeks between now and Gardeners' World Live, 13-17 June 2012, Adam Pasco will be answering a selection of your gardening questions.

If you'd prefer to ask Adam a question in person, you can do so at the Gardeners' World Theatre at Gardeners' World Live, where he'll be appearing regularly. Save 10% on your show tickets by booking now:

Tel: 0844 581 1344
Book online quote code GWNE




Last year I got a good set on my cherry, plum and apple trees. However, when the fruit was just a week or so old they were all wiped out by a sudden frost. At what point are newly formed fruits immune from frost damage? From Brian Nicol

Adam says: Fruit is most vulnerable to frost damage when in open flower, and this is as true of fruit trees as it is of soft fruits like strawberries and currants. Frost harms the sensitive anthers and filaments within flowers, so they cannot be pollinated and do not form fruits.

Although it may have appeared that small fruits were developing, damage to flowers meant these were not viable and aborted, falling to the ground. Once pollination has taken place I don't think mild frosts will do any harm, but very severe ones potentially could.

I always keep a few large sheets of fleece handy to throw over trees when in full open flower in the hope they'll provide a degree of protection. These are removed each morning to allow bees and pollinating insects full access. Remember that pollinating insects are not often active during cold weather. Even if frost didn't do any damage, if blossom isn't fully pollinated then fruits will not form.

I planted garlic last October. It was growing well but I've just noticed it is starting to go to seed. I have pulled a couple up, and there is only one bulb. Also, some of the leaves have rust spots on them. What's wrong? From From macdifficult

Adam says: Flowering is quite common on hardneck varieties of garlic. These are hardier varieties than softneck types, making them ideal for autumn planting. Garlic flowers are called 'scapes', and should be removed. However, don't waste them as they're edible, and can be added to stir fries for extra garlic flavour. I wouldn't expect bulbs packed with cloves to be fully formed yet, so be patient.

However, your biggest problem is rust, a debilitating fungus disease that also attacks leeks and onions. This disease is always worse after long periods of wet weather. Sadly there is no cure. Plants may survive a mild infection, but should be removed and destroyed if infection is bad, preventing it spreading onto the other crops mentioned. Do not put infected crops on the compost heap. Avoid growing garlic, leeks or onions on this site for at least three years. Steviefr also asks about garlic. He lives in North Yorkshire, and is worried that all the rain will cause bulbs to rot. Garlic does enjoy moist soil, but not waterlogging. As this has been the wettest April since records began over 100 years ago most of us have probably faced the wettest soil conditions in our gardens for many, many years. My garlic is still OK, and not suffering from rust, so I do hope others will have a successful crop despite the weather.

I have a garden arch set in my lawn. Would it be possible to grow a Clematis montana 'Rubens' in a pot and train it over the arch? If so, what is the minimum size pot, and would clay or plastic be best? From spring2

Adam says: Although you could grow clematis in a very large container I would always prefer planting in the ground, so do consider this if possible. Clematis montana is a vigorous spring-flowering climber, and could be planted in a large pot perhaps 60cm or more across and deep. A plastic pot with good drainage holes in its base will retain more moisture than a terracotta one. Shrubs should always be planted in loam-based John Innes No.3 compost.

Anything growing in a pot relies on you for its care, and in particular regular watering. If you can't commit to weekly/fortnightly watering through summer then avoid growing in a pot, and plant in the ground instead.

I bought an aeonium a couple of weeks ago, but it keeps dropping its leaves. They are going yellow and see-through, and then falling. It is in a north-facing window and at room temperature without heating. What's wrong? From Mark Burbidge

Adam says: I love these tender succulent plants, native to Canary Islands, North Africa and Madeira. This tells you the sort of conditions they require – warm and bright. I think the leaf-drop you've been experiencing is entirely natural and to be expected in the conditions you've provided. Older leaves continually fall, leaving long bare stems with rosettes of leaves at their tip. I'd recommend finding a brighter windowsill to provide more light. Shoots become elongated and gradually bend towards the light when growing indoors, so turn pots regularly.

An ideal temperature would be around 16˚C, but aeoniums will tolerate lower winter temperatures provided they don't drop below freezing, which will kill them. Move pots outside during summer to enjoy warm and bright conditions similar to their Mediterranean origins.

I have a large amount of clover in patches over one acre of lawn. Can you advise me on getting rid of it. Would chemical treatments be OK to use with animals? From Harry Bristow

Adam says: Clover is often viewed as a valuable lawn weed, and some seed companies even add a small-leaved 'micro-clover' to their lawn seed mix. Their flowers are much enjoyed by bees, and during periods of drought clover often remains green even when grass has browned-off.

If you do want to get rid of it, several suitable lawn herbicides are available. No garden chemical can be sold that when used as directed poses any danger to pets or children, so these should be safe to use. However, I wouldn't let grazing animals feed on treated or dead clover. Keep animals away from the treatment clover, and rake out remains before letting them back. Once the clover is gone you'll need to re-sow with grass seed or weeds will quickly take its place.

Should I pinch out the tips of my cosmos seedlings? From Arjuska

Adam says: You've asked a very interesting question, and one that often confuses me. Pinching out the growing tip of a plant is often recommended to encourage plants to produce more shoots, and become bushier. No, I would not pinch out cosmos seedlings, but plant them out as they are, allowing them to branch naturally as they develop. I do not pinch out zininias or snapdragons, but do find some bedding plants benefit from pinching, like petunias. I also pinch out sweet peas, dahlias, fuchsias, marguerites, heliotrope, coleus, osteospermum, dianthus and others to encourage plenty of shoots to develop.

Most of my garden plants, including new ones I've just put in, have white spots on them. Can you tell me what causes this and how can I stop it. I'm pretty new to doing the garden. From Francis Jarvis

Adam says: This sounds like hail damage. I experienced several extreme hailstorms in my Peterborough garden during April, and I believe many other areas did too. If you walk out into a hailstorm you'll know how painful it can be on your face, so just imagine what damage these sharp and fast-moving chunks of ice can do to delicate leaves.

I've also noticed small white spots on many leaves, especially the pots of lilies I'd just moved outside. These spots are actually tiny cuts in the epidermis of the leaf. Sadly the damage is done, and they will not repair. Any new leaves that unfold should be perfect, provided hail doesn't return!

Little can be done to protect plants growing outside, but if I ever hear that hail is forecast I do try and move plants in pots under cover. Alternatively, throw a sheet of fleece or fine netting over plants to provide some protection.

Recent hailstones have damaged my young plants and rhubarb. Will plants recover, and will my rhubarb be edible? From rtcurry

Adam says: As I've said in the previous answer, sever hail storms have been very damaging in some areas, with the size and force of hail actually puncturing and tearing leaves.

A couple of years ago a hailstorm in May ripped through my hostas, ruining the display for the whole year! With a quick glance the holes could have been mistaken for snail or slug damage, but Mother Nature was really to blame. Very damaged leaves should be removed to prevent them rotting. Although your rhubarb leaves have been damaged the rhubarb stalks will still be fine to eat.

I have agapanthus in pots, but because of the water shortage would like to plant them in the garden borders. Is this OK? From Gill Gardner

Adam says: These South African natives can tolerate a fair degree of drought, so although they could be planted in the ground I'd prefer keeping them in pots.

Agapanthus always flower best when allowed to get quite pot bound, so this is another advantage of keeping them in pots. Many of my agapanthus have been in pots for over five years, and are completely full of roots. These agapanthus still flower well, but I do always remember to feed with liquid fertiliser every week during the growing season from May to September. Varieties vary in hardiness, too, so in districts with cold and wet winters, and on heavy soils, they may not survive. Plants in pots are easier to move into an unheated greenhouse or conservatory to provide winter protection. They're also easier to move around and create summer displays, and pots can even be positioned or sunk into borders while in flower.

These South African natives can tolerate a fair degree of drought, so although they could be planted in the ground I'd prefer keeping them in pots.

When is the right time to trim a laurel hedge? From Jill Ashe

Adam says: Cherry laurel often needs pruning several times through summer, and the number of cuts really depends on how neat and pristine you want your hedge to look. The more often you cut, the neater it will look. Avoid cutting hedges at any time when birds are nesting, so check carefully before you cut.

You could give laurel hedges their first cut in May or early June, and again in July or August. However, do not cut any later than the end of August or there will not be time for new shoots to grow, and gaps can develop. Choose dry weather for cutting, and pruning cuts heal more quickly so disease is less likely to infect plants. Although slower, always try to use secateurs for pruning by hand rather than using a hedge cutter. By cutting off individual shoots you'll avoid damaging leaves. Hedge cutters sever leaves that then die back and look unsightly.

Aim to stop the height of the hedge at your desired height, using a length of string as a level guide rather than try and judge this by eye.

Laurel makes a robust hedging plant, and will send shoots out of old wood. This allows old or overgrown hedges to be cut back severely, and they will re-grow!


Ask Adam: part one

Ask Adam: part two

Ask Adam: part three

Ask Adam: part four

Ask Adam: part six