Sphere of Influence
Guest writer: Rachael Matthews | Portrait photo Paul McCredie | NZ Gardener Magazine, 2024
Topiary balls are a design feature for every garden style. Here are the best plants to use, expert tips to achieve a more organic shape, and advice on integrating them into your garden design.
Any hedging plant that has lots of little branches, with small leaves, that respond well to pruning, could be worked into a ball shape. The more you prune hedges and balls, the denser and more defined they will become.
Rachael Matthews calls these caterpillar balls. Instead of straight lines of hedge, the balls (Buxus sempervirens) are plantred in a gently winding caterpillar formation, and edged in a wide band of black mondo grass (Phiiopogon planiscapus “Nigrescens”). The flowering hedge behind is Viburnum tinus “Eve Price”. The conifer columns are Thuja “Smaragd”.
Most people know me as Mrs Hedge, but really, I should be known as Mrs Balls! Or perhaps, Ms Spheres – as my landscape architect friends prefer to call them.
I am a garden designer & I grow plants that add evergreen structure & style to a garden –plants that are pruned & trained to do a design job and provide the green backbone.
Rachael Matthews is the owner of Hedge Garden Design & Nursery in Wellington.
I make use of balls in my garden designs for many reasons. You can scatter them about and create pockets for planting foliage and flowers. They provide contrast, solidity, form and rhythm. They are invaluable in winter, when other seasonal plants are having some down time. They do a very similar job as hedges, but you don’t get into trouble when one dies and you’re left with a gap in your line.
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Pittosporum Golfball for evergreen structure between pockets of contrasting foliage and seasonal flowers. Hydrangea “Limelight” (on the right & in the garden behind) with tall windflowers (Japanese anemones) bollowing above. In the foreground is the finger-like evergreen foliage of Hellebous foetidus, with green flowers in winter and early spring.
Round is a more natural organic shape and a foil to hard lines. Instead of planting a straight line in one kind of hedge, you can introduce more variety & interest by using mixed kinds of balls, and in different sizes.
I also use them in combination with hedges to make the hedges more interesting – like a full stop on ends and corners, and to break up a straight line. I once reused some wonky buxus standards, and planted them inside the hedge itself, to create a domed effect.
Their round shape also suits any pot shape.
Buxus sempervirens in a formal garden – a great example of using balls on corners in combination with hedging. Edged with black mondo grass.
Which plants make good balls?
Any hedging plant that has lots of little branches, with small leaves, that respond well to pruning, could be worked into a ball shape. The more you prune hedges and balls, the denser and more defined they will become.
Smaller leaved plants work better for smaller sized balls; and larger leaved plants look better on larger balls.
Always select a small growing, moundy cultivar, so they don’t grow too big, and you don’t have to prune them too often. Once formed, you should only need to prune balls two-four times a year.
There are several new cultivars available – improvements on the parent plant - that are smaller growing with a naturally dense moundy shape. All their parent plants want to grow bigger than 3m, but cultivars Pittosporum “Golfball”, Westringia “Aussie Box”, and Polygala “Petite Butterflies” will stay naturally moundy at around 1m.
Finally, select a plant that is suitable to your conditions and style of your garden.
This is a practical but beautiful back garden design for a busy family with teenagers. There are pavers in the grass to keep the feet dry for frequent access to the washing line. And concrete lawn edging at the base of the wall so it’s easier to mow. The balls are planted in a raised garden to protect the plants from soccer games on the lawn. This was taken in early summer. Pittosporum “Golfball” are interplanted with white flowering hydrangeas (not in flower yet) and evergreen Buxus “Graham Blandy” columns for vertical evergreen structure.
How to shape & trim balls
In the past, we’ve been able to buy ball shaped training frames – but I haven’t seen any around for a while – and I have always trimmed my topiaries by eye.
First of all, remember that If you make a mistake, don’t worry, it will grow back …like hair.
When you’re trimming a plant into a ball, stand over the top to get a nice round shape from a birds eye point of view. Then walk around the outside to get a rounded profile. Just trim a little bit off at a time, walking around the ball in circles. Start by trimming your balls to look like a square – then curve the corners and edges. Mine can often look a bit flat topped, and this is fixed by flattening the sides.
I do most of the trimming with hedge trimmers, turned upside down to get a slight inwards curve. Then finish off the finer detail with shorter bladed and more precise snips. I don’t think you need to use special topiary shears. And looped handles, like scissors, give me blisters. My favourite trimmers are long handled ARS KR-1000 hedge shears – they very sharp and lightweight, with no pincer movement and an easy action on my (arthritic) hands, and are easier on the back as you don’t need to bend over as much.
Ball shaped-Buxus Green Gem adds solidity to a wonderfully layered bed.
My pick for Top Ball
No. 1 is Buxus “Green Gem, one of the most disease resistant buxus cultivars. It is better looking than and superior to the traditional Buxus sempervirens, producing fresh green foliage year round. Buxus is so slow growing (5-10cm a year), and is therefore more expensive, but it’s also longer lasting and lower maintenance, and a better option in the long run, plus it does well in pots.
If you’re starting from scratch and want to save a bit of money or speed up the process, group together three plants to grow into one larger ball. You could also start with bigger plants. I chopped up my established hedge at home, and turned it into a ball border. It took about four years to come right. So don’t give up if you go down this path, they will come right in time.
Buxus balls are like an anchor plant, and suit the widest range of conditions. You can add the other balls for variety and to suit your style and situation. I usually make a combination of three different balls. Plus, including cheaper and faster-growing plants in the mix is a good way to manage overall costs.
If you’re starting from scratch and want to save a bit of money or speed up the process, group together three plants to grow into one larger ball.
Bay is better suited to growing as a ball rather than as a traditional standard because it sends up suckers from its base.
Before and after: I chopped up an old Buxus sempervirens hedge from another part of the garden and planted “Green Gem” balls inbetween. Buxus is slow growing, and the hedge took about four years to reshape and come right.
Ball ideas for different garden styles
The edible garden – Bay laurel (Laurus nobilis) is better suited to growing as a ball rather than as a traditional standard because it sends up suckers from its base. NZ cranberry, (Myrtus ugni ) has a delectable fragrance of toffee fruit warmed in summer sun.
Bay is better suited to growing as a ball rather than as a traditional standard because it sends up suckers from its base.
Bay laurel (Laurus nobilis) with a mix of balls in contrasting shades of green.
Coastal & dry Mediterranean-style gardens – Silver-leaved plants are more drought tolerant, so choose a combination of corokia, Westringia “Aussie Box” or cultivars, Teucrium fruticans, Pittosporum “Silverball”, and lavenders .
Many of my customers love lavender, but you need the right soil & climate. Lavenders really do prefer the south of France, with its limey, free-draining soil and plenty of sunshine – not heavy clay and lots of rain. But French lavender (Lavandula dentata) and English lavender (Lavandula angustifiolia) can be pruned after flowering into a dense ball shape (and use offcuts for lavender pillows).
From left: Buxus “Green Gem”; Pittosporum Golfball”; Westringia “Aussie Box”; Ilex crenata “Heleri”.
Fragrant, formal, green & white gardens – Osmanthus “Pearly Gates” has fragrant white flowers in winter. I grow them in my ball border at home.
Compact white-flowering hawthorn cultivars such as Rhaphiolepis indica “Fergusonii” and R. “Oriental Pearl” are undiscovered & under-used in New Zealand gardens – they are very tough, compact growing, and beautiful.
Ilex crenata “Helleri” is a good alternative to buxus, as is Abelia “Snow Showers”.
I find Euonymus “Emerald Gem” doesn’t shape well into a ball - it’s a bit stiff. And I don’t tend to use traditional hedging plants like Viburnum tinus “Eve Price” or Portuguese laurels, (Prunus lusitanica) as balls or hedges, because they are very prone to thrip insects and require a (carcinogenic) spraying regime to manage insect damage.
The only problem with corokia is that they are prone to scale insect, so I prefer to use them as balls, rather than hedges, and if one dies you’re not left with a missing tooth.
From left: Corokia “Geenty’s Ghost”; Abelia “Snow Showers”; Corokia “Frosted Chocolate”; Muehlenbeckia astonii.
Native gardens – Native plants are well suited to New Zealand conditions, and can be used in traditional as well as contemporary designs.
My go-to native ball is Pittosporum “Golfball”. And I ’m currently trying out a new and promising cultivar Pittosporum “Pot Belly” as a compact and more readily available culitivar than “Tobia”.
Smaller leaved corokias such as C. “Geenty’s Ghost” (silver) or “Pipsqueak” (greener) suit smaller balls; and larger leaved “Frosted Chocolate” & “Geenty’s Green” look better on medium to larger growing balls. The only problem with corokias is that they are prone to scale insect; so I prefer to use them as balls, rather than hedges, and if one dies you’re not left with a missing tooth.
Muehlenbeckia astonii is like an industrial designer’s plant - a bit edgey. It is used to great inspirational effect in the Auckland Botanic Gardens. It is particularly beautiful when water droplets are caught on its wirey bronze stems.
I don’t tend to use hebes much (unless my clients request them) because they don’t respond well to pruning if left for too long, and they are short-lived. To maintain their size and shape, it’s best to trim them lightly straight after flowering, and don’t prune into hard wood (they seldom grow back). I also avoid coprosmas. They are colourful, but I don’t use them as balls because I find them too stiff to respond well to trimming and shaping.
Grasses are an interesting and versatile option, and do the same job as balls - providing evergreen structure, contrast and pockets for planting inbetween.
From left: New Zealand cranberry (Myrtus ugni); Polygala “Petite Butterfly”; Lavender (Lavandula stoechas); Teucrium fruticans.
Pretty flower garden – Polygala “Petite Butterflies”, Teucrium fruticans, and lavender are all gorgeous in combinations, especially with green foliage balls as a foil. But you can have too many flowers and busyness – and I tend to leave the flower show to the plants inbetween.
Silver germander (Teucrium fruiticans) is fast growing and requires a lot more trimming than other plants. But the leaves are the most beautiful shade of duck egg blue - there’s nothing else quite like them. So I always suggest planting just a few of these higher maintenance blue balls in the garden to bring in the gorgeousness, and as better alternative to a long line of hedge, which is a lot of hard work.