Ask Adam: part six

Your questions answered

Welcome to the final installment of our Q&A series with Adam Pasco, editor of Gardeners' World Magazine. Discover if Adam answered your gardening question, below.

If you'd like 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:

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How do I propagate camellias? From katiesgirl

Adam says: Camellia is not an easy shrub to propagate, and I'll admit that I've never done it myself. However, when I worked on a commercial nursery in Surrey many years ago I did watch it being done.

Two techniques were used. The first was bench grafting, where a shoot from the flower variety was grafted onto the rootstock of a strong-growing camellia. This is a specialist technique, and was carried out by experienced propagators who had been grafting for years. Grafting was carried out on pot grown rootstocks early in the year, and plants kept in a warm greenhouse until the graft had taken.

The second technique is to take cuttings using shoot tips. Semi-ripe cuttings are taken in during summer/early autumn, dipping their cut ends in hormone rooting compound, and placing into an open, ericaceous compost in a propagator to root. Alternatively, try taking hardwood cuttings from autumn into winter, using a heated propagator to provide a temperature of around 16-20˚C to encourage rooting.

Be patient, as rooted cuttings can take 3-4 years to form a shrub carrying flowers.

I have oleander plants which have never flowered, although I've tried growing in pots as well as soil. They were grown from cuttings taken from my mother's plants that flowered all the time. What's the problem? From nulusaccmancieii

Adam says: I sympathise, as I've never had great success getting oleander (Nerium oleander) to flower outside in my Midlands garden. Commonly seen growing into large evergreen flowering shrubs in Mediterranean countries, the trick is to mimic these conditions in your own garden.

Oleander should be grown in a large pot using a loam-based compost, and pot will need moving indoors to a heated greenhouse or conservatory for much of the year. Once conditions warm up later in May the pots can be moved outside to a warm position in full sun. Choose a south-facing site if you have one, backed by a wall that warms in the sun. Plants require regular watering, especially in pots, although they'll tolerate drought. Give regular feeds with a high potash fertiliser to encourage flowering rather than leafy growth.

I have vine weevil in my containers. How can I treat them without affecting my flowers, and with what? From RobertEliott

Adam says: Vine weevil is a damaging pest. The adult weevils are a large grey beetle about 1-2cm long that eat notches out of the edges of leaves of many types of shrub. They're successful pests as they are all female, do not need to mate, and every weevil is capable of laying eggs!

These eggs are laid in soil or compost, and hatch into C-shaped cream-coloured grubs with brown heads that eat away at the roots and underground parts of numerous plants. They're very partial to cyclamen, begonia tubers, and the roots of strawberries, fuchsias, primulas, and many more. Root damage can cause plants to wilt or die.

Adults are usually active at night, so check plants, picking off and destroying any you find. Grubs discovered in compost should be squashed, but you won't have found them all. Treat compost or soil around plants with a biological control nematode or suitable pesticide. You'll need to completely drench compost so that the treatment comes into contact with the pests. Gardeners have come up with other innovative methods of control, like forming barriers around the edge of pots with petroleum gel or even standing pots on an island surrounded by a moat of water. An internet search could reveal more ideas.

The top leaves on a red acer tree have all turned brown, damaged by frost and bitter winds. Is it best to take the dead leaves off? From philipgardner

Adam says: This sounds like a Japanese maple, and I grow a couple in large patio pots. They're very susceptible to wind scorch, with some varieties growing best in a shaded position so that leaves don't get scorched in the sun.

Warm temperatures in March encouraged lots of plants into growth, only to be caught by the frost and cold weather that followed. Let's hope the cold just killed the leaves and not whole shoots, so carefully pick off the dry leaves to tidy the display. If new leaves don't sprout from these shoots by mid-summer then prune back to a leaf to remove the dead tip.

Keep acers in pots regularly watered, as drying winds can dehydrate and damage leaves. And next spring keep a large piece of fleece handy to throw over your acer to protect it if frost is forecast.

What appears to be black soot is covering the leaves on my pieris and rhododendron. What can I do? From sheddy

Adam says: This sounds like sooty mould, and I've found it in the past covering the surface of camellia leaves. This mould is growing on honeydew dripping down onto the leaf from above where a pest is feeding. The most likely pest is scale insect or possibly an aphid, so inspect the underside of leaves to see what you can find. Treat the pest with a suitable pesticide and you'll stop honeydew falling. Then gently wash off the sooty mould. This can get dry and hard, making it difficult to remove unless softened first with soapy water.

This layer of sooty mould does look unsightly and stop light reaching the leaves, so do spend time removing it. I've used a soft cloth or sponge to do this. Then give these and other ericaceous plants a generous liquid feed with a solution of iron sequestrene.

How can I prevent leatherjackets in my lawn? I've just had the turf relayed after first treating the area for pests, but how can I stop this happening again? From annie8

Adam says: Leatherjackets are large grubs feeding on grass and plant roots that hatch out into crane flies, or daddy longlegs, later in autumn.

Many pests are just part of our natural environment, like ants, so preventing them coming into your garden is not an option.

However, you may feel it is worth investing in a biological control treatment for your lawn to kill any leatherjackets that could still be feeding, hidden from your view. Most natural gardening companies sell biological controls, so ask them about treatments for leatherjackets. These are a microscopic nematodes that are mixed with water and applied to lawns and borders. The nematodes move through soil moisture to search out pests, releasing bacteria into them as they feed, killing the leatherjackets.

By reducing leatherjacket populations you'll stop the damage they cause, and also that of birds and other animals scratching away at your lawn to reach a tasty meal.

I've heard that Tenby daffodils (Narcissus obvallaris) reproduce from seed rather than by producing clumps of new bulbs. When is the best time to take the seed, and how do you get it to germinate in Yorkshire?

Adam says: The Tenby Daffodil is a lovely yellow species to naturalise in wild areas, flowering in February/March on short stems only about 25-30cm long. As far as I'm aware the bulbs will divide and form larger clumps year on year, so just water clumps with a liquid feed now that flowering is over to boost bulb development to improve flowering in future years. Most daffodils will form seed heads, and I prefer picking these off so that energy goes into bulb growth and is not wasted forming seeds. However, you could try leaving seed heads to fully ripen on plants. These could simply be left to shed their seed onto surrounding soil, where hopefully some will germinate and grow. Alternatively, collect ripe seeds and sow in large pots of compost. Keep seedlings in these pots for a couple of years so that a bulb develops before transplanting.

Then be patient, as bulbs usually take 3-4 years to reach flowering size from seed.

Ask Adam: part one

Ask Adam: part two

Ask Adam: part three

Ask Adam: part four

Ask Adam: part five