Monthly Q&A February

Matt Biggs says: Plums need a warm, sheltered spot, ideally on slightly acidic soils. Protect blossom from frost with horticultural fleece. Feed in late winter with high potash general fertiliser and maintain a grass-free circle at least 1m around the tree. Prune in summer to keep an open form. Leaf curling aphid and mealy plum aphid do not generally affect productivity. Squash small populations by hand, encourage ladybirds, lacewings, hoverflies and earwigs, or spray with soft soap or plant invigorator and continue with winter wash. Plum rust does little damage overall; simply remove fallen leaves and dispose away from the garden.

I’ve got a cordyline in the garden which is sprouting shoots at its base. Can I propagate these or will it kill the main plant? Joanne, Doncaster

Humaira Ikram says: I’ve found that cordylines are the most robust and tenacious plants. Examples of this are that there's one that has grown in a crack in my garden and is now 1.5m tall. I should have removed it, but it seemed heartless after it had found such a tiny little niche. And the other is a rootball that was abandoned on top of a compost heap. It now has three small plants growing away. So I would say yes! Cut off the small plants with a sharp knife and pot them up in a free-draining, peat-free compost, put them somewhere with sunlight and give them a watering or misting, and wait. The main plant should be fine if you remove the suckers.

I have a family apple tree with three varieties but one is growing upwards, whilst the other two grow downwards. Can I train the upward-growing variety to grow downwards? Amanda, Kent

Matt Biggs says: Cut back the previous year’s growth by one to two thirds in late winter, to encourage side branching. The same branches are then cut back each winter by one third to encourage the formation of side branches and fruiting spurs. ‘Festooning’ is only possible if the stem is still flexible. Carefully bending the stem towards the horizontal, wrap the tip with soft sponge to prevent bark damage, then anchor it to the ground or lower down the tree stake with string. Alternatively weigh them down towards the horizontal with a heavy stone or brick until they stay there naturally.

Why are my camellia leaves yellow? It flowers but a lot of the leaves are yellow or partly yellow. Eeva, Essex

Humaira Ikram says: I love a camellia and usually they are pretty trouble-free. Yellowing leaves could be a few things. Camellias like an acidic soil so if they are in an alkaline soil this can impede their ability to take up iron and other nutrients, and this can cause a yellowing of the leaves. It could be from underwatering or overwatering, or it could be a virus. The only way to deal with these viruses is to cut out all infected materials and dispose of them carefully. Make sure that you disinfect your tools afterwards.

I planted a goji berry about three years ago. So far there have been no flowers, let alone fruit! What might I be doing wrong? Graham, Moray

Matt Biggs says: Goji berries prefer an open, sunny site, tolerate some shade and should ideally be trained against a wall or fence. Improve the soil with plenty of well-rotted organic matter before planting, mulch around the base in spring and feed each spring with a high-potash general fertiliser. They take three years to establish and flower and fruit on the previous year’s growth. Remove badly placed stems or those that are growing in the wrong direction in spring, along with some of the older wood at the base, any that are dead or weak, and cut back long stems to a well-placed branch.

We have hawthorn trees which have become covered in ivy. Will this eventually kill the trees and should it be removed? Jill, Nottinghamshire

Humaira Ikram says: Ivy is really misunderstood as a plant. It’s such a great source of nectar for pollinators and insects later on in the year when very little else is about, and it also creates lots of nooks and crannies for birds and wildlife to live in. It is a bit of a thug, but it usually does not affect trees that it grows through. It can become heavy and unwieldy in a storm, but really it's quite a good thing all round. However, if you really want to be able to see the hawthorns then, yes, of course remove the ivy – but be aware that it is part of the ecosystem of your garden and removing it will mean it takes a few years for the garden to get back to its equilibrium.

When is the best time to start off ranunculus? I've tried them in spring, they grew rapidly but gave up before flowering and had aphids. Gill, Livingston

Matt Biggs says: Soak them for 12 hours before planting from late summer to early winter, with the ‘fingers’ facing down, in moist and fertile but well-drained soil in full sun to part shade, in a warm, sheltered position away from cold winds. Add organic matter before planting if necessary. Water after planting, and keep the soil constantly moist but do not splash water on the leaves as this encourages disease. Fertilise with high-potash general fertiliser every two weeks, until they start to die back. Mulching around plants controls weeds and conserves moisture. Control slugs, snails and aphids using environmentally friendly methods.

How do I get rid of wild garlic plants? Linda, Northumberland

Humaira Ikram says: This is a tricky one! One of the benefits of wild garlic is that it looks lovely in the spring. They produce a soft, white carpet of umbels, and early pollinators really benefit from having these open flowers with their good source of nectar at that time. They taste pretty good too, if eaten in moderation. However, once established they are tricky or labour-intensive to remove. Out in the wilds there is usually no real issue, but in a garden you may want to plant something else that wouldn’t be overtaken by the thuggishness of this plant.

I find that if you can get it early, and dig out before it gets established, that’s the best way. Usually you don’t have that option, but really it’s about digging and being really thorough about removing all of the bulbs, which can be tiny. If you do this year after year it will weaken the crop. You could also cover an area with a black cloth or sheeting to remove sunlight, or as a last resort you could remove the topsoil to a spade's depth, but really the management of this is in being vigilant and removing any new plants. The other option is that you can start a wild garlic pesto company and gather, forage and sell the produce. When life gives you lemons...

Can you suggest any evergreen plants suitable for hedging that would grow on wet peat? Kathleen, Argyll

Matt Biggs says: Planting the hedge on ridges at least 60cm wide above the surrounding water level will help plant growth. Semi-formal hedges can be created from upright forms of camellia like Camellia x williamsii ‘E.G. Waterhouse’ with clear pink flowers, ‘Gwavas’ with double, pink blooms, or white-flowered Camellia japonica ‘Elizabeth Cooper’. All of these would be happy in your part of Scotland. Alternatively, try Erica arborea ‘Albert’s Gold’ with golden foliage and white flowers, which can be lightly trimmed to maintain its shape. There are many rhododenrons to choose from depending on the space available, including pink-flowered Rhododendron ‘Rocket’ and creamy-white flowered ‘Phyllis Korn’.

Is it sensible to plant a raised vegetable bed in front of an Air Source Heat Pump? Tim, Oxford

Humaira Ikram says: The easy answer is "no". Pumps and conditioning units have a different microclimate around them. This can be quite labour-intensive as you will have to be especially vigilant with watering and really do need to pick very robust plants to be able to even have a chance of dealing with these extreme conditions. I would keep plants away from all pumps if possible – maybe put up a screen to hide it and also to disperse the air more widely and consistently.

Our experts

Ashley Edwards

As a head gardener with charity Horatio’s Garden, Ashley enjoys sharing his passion for plants

Humaira Ikram

Humaira has worked as a garden designer for over 10 years and runs a garden design course

Christine Walkden

Garden writer Christine appears on BBC1's The One Show. She is also a lecturer and tour leader

Matt Biggs

Matt trained at Kew and has been gardening professionally for more than 30 years

More of your questions answered:

• Watch Adam Frost's answers to your questions in January
• Your December questions
• Your November questions