The most common garden dilemmas, and how to solve them – from pests to pruning

Writer Tom Brown, head gardener at West Dean College, offers advice for 10 common gardening problems - Russell Sach

There are a number of, dare I say, thorny problems that many of us wrestle with in our gardens, myself included. Ahead of National Gardening Week next week, the RHS recently revealed that its Gardening Advice Service received a record number of queries in 2025 – 121,081, to be exact. Among the queries were many related to pruning, diseases and pests.

Here are 10 of the most common ones, along with my thoughts and solutions to these universally frustrating gardening issues.

1. Why are the leaves on my rose speckled and/or black?

Speckled, yellowing and black spots on rose leaves are generally a sign of stress during spring and summer - Boy Anupong

Speckled, yellowing and black leaves are generally a sign of stress, exacerbated during periods of hot, dry weather. There are several black-spot treatments available to buy, but, in my experience, if the conditions are wrong for that rose, it’ll be like pushing a large boulder uphill and it will be very expensive to try to manage those foliar symptoms.

Generally, our gardens are becoming hotter and drier places in the summer, and these are tough conditions for traditional roses, which can result in speckled leaves. However, there are several tougher species that are far more tolerant of those tricky conditions.

The Peter Beale and David Austin websites have lots of information about drought-tolerant roses and those suitable for poor soils, so even with less than clement conditions, we can still grow roses in our gardens.

2. Is there a simple winter pruning plan for an over-vigorous apple?

The rootstock of your apple is the driving force towards the vigour of your tree. When you’re planting a new tree, it’s well worth taking time to research the rootstock that you need for your garden situation. The rootstock is the main contributor to vigour, but some varieties like Bramley’s Seedling also tend to be very vigorous trees, compared to other varieties.

Tom suggests a five-year pruning schedule for out-of-control apple trees - Clara Molden for The Daily Telegraph

If your tree is out of scale and needs to be reduced, this should be carried out over a five-year period. This may seem like a long time, but the harder you prune a vigorous tree, the harder it will come back at you. Aim to remove no more than 20 per cent of the tree each winter, so over those five years you are gradually replacing the canopy, ultimately making the tree more compact. An open goblet-like shape with fewer upright branches is what you’re looking for.

Reduce congested areas and take fewer but slightly larger branches, which will avoid lots of little cuts resulting in a tree that resembles a bird’s nest.

3. Is this a macrophylla or paniculata hydrangea – and which pruning applies?

Different types of hydrangea require different pruning methods, and it can be quite difficult to tell them apart purely by their leaves when they’re not in flower.

The process of annually pruning the shrubs removes deadwood and encourages a compact and balanced shape, but if you miss the window of opportunity for a year or two it’s not the end of the world. If you’re unsure what type you have, don’t do any pruning in the spring and allow the hydrangeas to flower freely that summer. When they’re in full bloom it should be much easier to identify which species you have: paniculata hydrangeas have conical flowerheads, while macrophylla hydrangeas have round heads. Here’s how to prune each one.

Hydrangea macrophylla

Hydrangea macrophylla have round flowerheads, and are much more common on garden borders - zhuyongming

Wait until the buds begin to break in spring to identify the live and dead wood, then remove any dead stems, which are often brittle. To be certain, scrape the bark with a nail. Viable stems are green underneath the bark. Take out a couple of the oldest stems each year from the base to encourage growth, ultimately aiming for an open goblet shape.

Once the oldest stems have been removed, prune back to a strong pair of buds from the shoot tips on the remaining stems, removing any dead flowers or the extremities of the shoots which may have died back during the winter. Overzealous pruning of this species of hydrangea will lead to an absence of flowers.

Hydrangea paniculata

Paniculata varieties typically have conical flowerheads, as seen here with ‘Polar Bear’ - Rymasheuskaya Volha/iStockphoto

Paniculate hydrangeas will produce flowers on growth produced during that year. Prune in winter or early spring back to a strong pair of buds, 5cm from the origins of last year’s growth, for large flowers.

The harder you prune your paniculate hydrangeas, the later and larger the flowers will be. This will often come down to your aesthetic choice. Adventurous gardeners can prune stems back to varying lengths to achieve flowers of different sizes, produced over a longer period. While pruning, remove any dead or damaged growth, simplifying clusters of stems on an annual basis.

4. The leaves on my cherry tree are blotched – is it leaf spot?

Leaf scorch and leaf spot are common fungal diseases on many cherries. The best and only treatment to control the spread of these fungal diseases is good hygiene. As leaves fall, they transmit the fungi to the ground, which allows reinfection the following year.

Clear away any infected leaves and send them to landfill or incinerate them. Any brown leaves that persist on the tree through the winter should also be removed and disposed of in the same way. Mulching around the feeder roots of your tree will improve the general health of the tree, which will help to mask the symptoms. Prunus ‘Kanzan’ is said to be more resistant compared to other cultivars.

Cherry leaf spot is a common fungal disease that affects many cherry trees during the growing season - kazakovmaksim

A note on pruning: my advice when it comes to pruning cherries is to be incredibly minimal: over-pruned cherries rarely recover and you’re left with an ugly, stumpy tree. Simply remove any deadwood or crossing branches during the period of active growth from April through to October. Pruning during the winter will often lead to the disease silver leaf, which can be detrimental.

5. The leaves on my acer have edge scorch – is this due to the sun, wind or watering?

This is a really common problem. Many of us grow acers in pots, which can lead to more scorching due to the fluctuating conditions of the compost within the pot: the soil or compost in containers is far more prone to temperature fluctuations and dries out much more quickly than an established root system in the open ground.

Japanese maples thrive in conditions with moist soils and dappled shade, and thus can struggle when grown in pots - Richard Becker / Alamy Stock Photo

On the plus side, it’s very easy to find a new spot which should be more conducive to healthy growth. Acers like woodland conditions with moist, rich, leaf-mould-like soil and dappled shade from trees with a much higher canopy. There is a lot of shelter in these locations, and very little drying wind. Replicate these conditions for your acer as much as possible, placing it in a sheltered spot in a large enough pot so that it won’t dry out during the summer.

6. My potted camellia has yellowing leaves – should I re-pot or feed it?

Excessive loss of leaves, or yellowing leaves across the entirety of the plant, can be a result of the pH of your soil being too high. A simple pH test, which you can buy from a garden centre, will determine whether you have acidic-to-neutral soil in which you can grow these plants successfully.

Camellias that are grown in containers rely on us for their water and their nutrition. A liquid feed every fortnight from March to August would be beneficial, with an ericaceous feed. Liquid feeds often give very quick results and ensure that your camellia is well watered and fed through the summer months, which is when flower buds begin to grow.

Note: a lack of flowers can be a result of the plant drying out too much in the summer. Bud drop is also linked to erratic moisture levels within the root ball during those key months of late spring and summer.

7. Should I prune my wisteria in summer or winter ?

Although pruning will help to allow more light into the canopy and will help a little with the development of flowering spurs, I find that this work is not essential during the summer on established plants. Simply manage those whippy tendrils back to a couple of buds as they appear throughout the summer, unless you want to tie them in for extending the framework.

Wisteria pruning is not essential during the summer for established plants - Clara Molden for The Telegraph

Wisteria pruning, particularly of the flowering spurs, simply means having fewer but bigger flowers. I find wisteria can be equally as beautiful with many flowers, slightly smaller in size, so it’s one of those jobs in the summer that I don’t lose too much sleep over.

8. When should I cut back my clematis?

There are three main groups of clematis, all flowering at various times, and they require different types of pruning to avoid compromising that flowering period.

Group one clematis include the winter-flowering types and should be lightly pruned immediately after flowering, avoiding old wood, to give them enough time to produce flowering wood for next year.

Clematis montana is a group one clematis that should be pruned immediately after flowering, producing buds on the previous season’s growth - Kinga Krzeminska/Moment RF

Group two clematis tends to flower in early summer; simply remove any dead wood when shoots emerge and then lightly trim after flowering.

Group three tends to flower much later in the summer, and this is the group that can be pruned hard down to around 15cm from the ground each spring, as this leaves enough time for the clematis to grow and produce buds before the end of the summer.

9. What’s eating my viburnum leaves – beetles, aphids, or something else?

Viburnum leaf beetle is a common pest, leaving lacy, skeleton-like remains of foliage during the late spring and summer. It is not impossible to manage with the use of biological controls such as lacewing and ladybird larvae, but it’s very difficult to restrict those predators to your own garden without them flying next door.

As with many pests and diseases, trying to battle the problem can often leave us feeling frustrated and out of pocket. Viburnum species such as carlesii and plicatum cultivars are more resistant to the beetle and worth considering as replacements for long-suffering shrubs. In some cases, it is better to admit defeat and plant a species that is less susceptible.

A note on pruning: a healthy, mature viburnum should respond to hard pruning, but if an old shrub lacks vigour, a hard prune can sometimes tip it over the edge. Removing a third of your shrub each March over a number of years will cause far less of a shock to the plant and will increase your chances of successfully rejuvenating it.

Viburnum leaf beetle can prove to be a menace for many different viburnum species - Jacky Parker Photography

10. Why are the leaves of my rhododendron curling and pale?

All shrubs and trees require a few years to establish, and we should temper our expectations until those plants have settled in. Trees and shrubs simply need us to avoid extreme conditions such as waterlogging or prolonged drought to help them establish.

This often means ensuring that there’s reasonable drainage before planting and making sure that new trees and shrubs are watered for the first few summers until their root system is established and they can start to fend for themselves to a greater extent. Leaves curling or going pale can often be a sign of stress, due to too much water in the winter or not enough of it in the summer.

However, as with any ericaceous plant, it’s also worth carrying out a pH test to ensure that your soil is acidic-to-neutral, because a rhododendron will not thrive in a soil with a higher pH. Rhododendrons can be grown successfully in pots but require regular liquid ericaceous feed to keep them buoyant.

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