Trees for your garden – the complete guide

Trees create structure, impact, shade, vertical interest and privacy in a garden. They make it look established and of course they provide valuable nesting sites for birds and habitat for other creatures. Beyond these practical things, I feel trees give a garden its spirit – its soul if you like. They become like old friends. But trees aren’t cheap to buy. So you clearly don’t want to make a mistake when getting trees for your garden!

Happily, to help us get things right, Douglas Weale, the Tree Operations Manager at Westonbirt, The National Arboretum, has kindly agreed to answer some of my most pressing tree questions.

So for an expert view on selecting, planting and caring for those trees for your garden, read on…(by the way most of the photos in this piece are sadly not taken in my garden. They’re mostly pics I took at Westonbirt a couple of years ago. If they don’t inspire you to visit the place I don’t know what will – it’s stunning!)

What should we consider when choosing trees for the garden?

Autumn is a great time to buy and plant a new tree or shrub, as you can choose from both container-grown and bare-root trees. But before you leap in and start buying trees for your garden ask yourself:

• What final size tree are you looking for?
• What sort of canopy?
• Is the tree or shrub to be deciduous or evergreen?
• Single or multi-stemmed?
• Vigorous or slow growing?
• What is the spot in your garden like – is the soil dry or moist, rich or poor, in a sunny or shaded position?

These things will affect your choice of tree. But there are also practical things to consider.

What are the practical considerations when buying a tree?

If buying a specimen tree (semi-mature), you need to think about the practicality of bringing a large tree into the garden. What’s your access like, and the proximity to drainage pipes.

Think about how you are going to transport your tree home carefully. Never carry trees on roof racks or in open trailers unless they are wrapped in polythene sheet, as fast-moving air quickly harms them. Trees are not designed for an open-air driving experience!

You also need to decide between a bare-root or container-grown tree.

Bare-root or container-grown trees – what’s the difference?

Bare-root trees and plants are cheaper but only available in autumn and winter. Container-grown plants tend to be more expensive but available all year around. If you’re looking for fruit trees they are often available bare root.

How can I tell if the trees I’m buying for my garden are healthy?

There are a number of things to look out for. First-up beware ‘root girdling’ of containerised trees and shrubs, or dead fibrous roots. Such a pot bound plant is a sign of poor irrigation.

Also avoid trees with damaged roots, for example main roots that are torn, split, or stripped of fibrous growth. Avoid trees that show signs of pests, diseases, wounds to bark, dead or distorted foliage and uncovered or dry roots.

How should we plant trees?

Once you are home, plant your tree as soon as possible. But don’t rush the job, take care, paying attention to any specific planting instructions and be careful not to invalidate guarantees that may come with your tree.

Do what you can to give your trees the best start, thinking about time of year and location.

The traditional tree planting period is November through to March, however you can plant containerised trees at any time of year.

Choose a suitable location, planting trees when soils are moist and free from frost. Cultivated soils are generally better for root development and plant growth. Dig the planting pit to the correct depth – normally no deeper than the container. The width of the planting pit should be a minimum of one and a half times as large as the root-ball/container and up to a maximum of two times as wide, if the soil is compacted. Treat a tree or plant with care before and during planting.

What about aftercare?

Once you have planted your tree, its aftercare is essential. Key to establishing a newly planted tree is regular watering, especially in spring when the weather becomes drier and the tree starts to come into leaf, continuing until leaves drop in the autumn.

Water newly planted trees at least 2-3 times a week in the summer, with at least a full watering can of water. Applying water from the top of the planting pit, using a watering can with rose attachment, as this allows the water to percolate gently through the soil enabling the tree to make the most of it.

And don’t forget to regularly remove weeds as they compete with young plants for water and nutrients, restricting their growth. Keep at least a one-metre diameter weed free spot around the tree, and consider using sustainably sourced mulch (e.g., bark) to help in sites with soft ground. In rural locations, you may need to use a tree guard or fence to protect young, establishing trees from deer or rabbits.

How can I spot if a tree is struggling?

For a gardener this is basically about keeping a watchful eye on the health of your trees and plants. Things you will be looking for when you carry out a ‘tree health check’ are typically:

• Thinning leaves. A thinning crown, or when a usually leafy tree is looking sparse and thin, could signal a pest infestation from something like Oak processionary moth or a disease like ash dieback (caused by the fungus Hymenoscyphus fraxineus), which blocks the water transport systems in trees causing leaf loss or lack of nutrients.
• Discoloured or mis-shaped leaves – are the leaves as you would expect for the species of tree and time of year? Yellowing or brown leaves, or leaves falling early are signs that you need to investigate. Check the leaves to see if they are uniform in shape, size and colour. Yellow (chlorotic) leaves often indicate lack of nutrients or poor root function. This could be due to waterlogging, soil compaction or drought.
• Dead wood and crown die back. A healthy tree should put on new growth every year, increasing in both trunk and branch size. Check for branch tips on the crown of the tree, and growth at the end of branches. Lots of small dead twigs at the end of the branches, or whole branches dying off, is a big sign that the tree is stressed.
• Dead, flaking bark. The bark protects the tree from lots of external threats like storms, pests and diseases. If there’s a sap oozing from the bark at the stem, or trunk, then that indicates a problem within the cambium (layer of tissue that helps the tree grow by adding another layer of wood). A ‘bleed’ like this can mean either a bacterial or fungal infection, or an infection from Phytophthora, which are microscopic, fungus-like organisms that can cause dark fluid to ooze from the bark, running down the tree trunk. Insects can also cause this. For instance the great spruce bark beetle, Dendroctonus micans, causes the tree sap to run out of the holes the beetle makes after entering the trunk.
• The trunk. Keep an eye out for cavities, cracks, bulges and wounds – all of which can indicate possible structural damage, and act as entry points for pathogens (pests and disease).
• Roots. If tree roots are exposed and look damaged, or if some digging near the trees has brought them to the surface, then their feeding system is going to be disrupted.
• Timing is key, meaning you might need to note symptoms over time. For example, when looking at a beech tree (Fagus sylvatica) more dead wood or twigs may appear on the ground. That could mean the Meripilus giganteus fungi is present. You can only confirm this from June to September, when that fungus is in season.
• If in doubt, do consult a knowledgeable arborist (a tree specialist).

Westonbirt has some gorgeous acers, is there any advice you can give specifically for them?

We grow several species of acer at Westonbirt Arboretum, and these are some things we look for when checking their health:

• Maples can be prone to leaf scorch in windy or excessively sunny positions.
• Young leaves can be caught by frost.
• We avoid pruning Maples at the wrong time of year (January-July) as they will bleed from pruning cuts.
• Poor autumn colour or purple-leaved varieties turning green may suggest a lack of light, such as being in a very shady spot or where larger trees have overhanging branches. We take care to locate a plant carefully, taking shading into account. Pruning can help reduce shade from other plants.
• Maples are susceptible to Phytopthora root rot in wet soils. Verticillium wilt can also be a problem.
• Maples in dry soils may suffer from powdery mildew.

As you can see from this specific advice about acers, the sign a tree is struggling varies from one species to another. If you think your tree has a problem it is good to research the growing and health tips for that particular tree species, either in gardening books or via reputable online sources such as the RHS

How can people look after their trees given the dry spell we’ve had?

This is all about when and how frequently to water, along with how exactly you do your watering. Pay particular attention to newly planted trees and those looking stressed.

Keep the area around the tree weed free so that the tree isn’t competing with the weeds for water and nutrients. Putting bark down around the tree can help.

Do your best to use ‘grey water,’ collecting and using rainwater as much as possible. For a great list of tips see the Tree Council’s top ten tips for watering trees in a drought.

How do we need to adapt our tree care given climate change?

 I think we need to think broader than just tree care. The changing climate has a significant impact on the way we garden. It is time to consider how to make our gardens more resilient. We are experiencing more extreme weather events in the UK, giving rise to flash flooding and periods of drought or extreme cold.

Alongside this, the UK is facing pressure to build more homes, with the natural environment squeezed for space. So, garden resilience becomes more critical such as creating gardens that alleviate flood damage; this generally means using less concrete, paving or hard paths. We need to improve carbon sequestration i.e., capturing carbon dioxide from the atmosphere. Plants do this, so planting trees helps! And we can focus on providing, or reinstating, habitats for wildlife to maintain biodiversity, which can also help decrease the threat from pests and disease.

Planting stock adapted to hotter, drier climates doesn’t mean simply selecting Mediterranean and exotic trees. They may suffer from unseasonal frost damage as we do still have occasional cold winters.

What trees like hot dry conditions?

The following trees are tolerant of hot, dry conditions and all of them can be seen in the collection at Westonbirt Arboretum, so do look out for them when you next visit:

Small trees for a garden:

• Gleditsia triacanthos: Common name Honey Locust, the yellow leafed cultivar ‘Sunburst’ is ideal for garden use, with bright yellow young leaves turning light green by late summer and is smaller than the green leafed species.
• Crataegus persimilis ‘Prunifolia’: Common name: Plum leaf hawthorn. Small, spreading, evergreen tree with bark flaking attractively into cream, grey and green patches during summer. A good garden tree.

Medium trees for a garden:

• Ginkgo biloba: A robust deciduous tree with striking foliage. Can be seen at Westonbirt Arboretum, within the Old Arboretum. Also known as Maidenhair tree, its conservation status is ‘Endangered’. A popular, well-loved tree, the gorgeous maidenhair tree is under threat in the wild from habitat loss due to deforestation to make way for agriculture and exploitation of its timber for construction.
• Eucalyptus pauciflora subsp. niphophila: Common name Snow Gum. A particularly hardy evergreen tree noted for its flaking and colourful bark. Note, eucalyptus have been frequently implicated in subsidence so be wary of planting near buildings.
• Pyrus calleryana var. fauriei (syn.)‎: Common name Pear. A very robust deciduous tree widely used in landscaping.

Large trees for a garden:

• Cedrus atlantica: A large conifer, conical when young and spreading when taller. The blue leaved form ‘Glauca’ is especially spectacular as a specimen tree for very large gardens. Common name Atlas cedar this is a tree that can also be seen at Westonbirt Arboretum, within Silk Wood. Many individuals of this species are protected within National Parks and are being monitored for die-back. Its conservation status is ‘Endangered’.
• Quercus ilex: Common name: Holm oak, of Family: Fagaceae (Beech). A large spreading evergreen with attractive green foliage.
• Acer rubrum: Common name Red maple. A large spreading deciduous tree with remarkable autumn colour.
• Taxodium distichum: Common name: Swamp cypress. A large deciduous conifer, fairly tolerant of drought and very tolerant of waterlogging. Beautiful golden hues in Autumn. Suited to very large gardens.

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I can’t thank Douglas Weale and the brilliant team at Westonbirt Arboretum enough for this amazing advice. It’s certainly given me plenty of food for thought as I look at the trees in my garden and think about how I can keep them healthy and happy.

Here’s to happy trees – and happy gardening – x

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Choosing trees for your garden? Why not visit Westonbirt Arboretum

If you are thinking about trees for your garden, do fit in a trip to the amazing arboretum. It has the most incredible array of trees. I’m lucky enough to live relatively near it and no matter what time of year I visit, I love it. So if you’ve the chance to go – do! In the meantime, check out my Westonbirt blog.

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