13 May 2023

Top ten bonsai care tips - from a Kew Gardens expert

Kew's bonsai specialist Richard Kernick on how to get the most out of your tiny trees

By Ellie Wilson


Richard Kernick has been in the bonsai game for more than thirty years. As the bonsai expert at Kew Gardens for the past decade, he's in charge of more than 80 bonsai trees, including some that are over 200 years old.

You can find Kew’s bonsai collection at the Bonsai House, at the end of the Kitchen Garden. Different trees are on display according to the seasons, so it’s always worth a visit.

For World Bonsai Day, here are ten of Richard’s favourite tips for growing healthy, beautiful bonsai.

Let it grow

A bonsai tree doesn’t always have to be “bonsai shaped”. There’s no need to pinch, snip and shorten branches as soon as they start to grow.

I leave most of the trees in the Kew collection to grow uninterrupted throughout the spring and early summer before carrying out a ‘June prune,’ when the long spring growth is shortened or removed," says Richard. “This early spring growth spurt significantly improves the root production and the health of the tree."

Shot from above, a plastic pot plant dish holds some clipped conifer needles, beside three bonsai tools
Bonsai tools and clippings © RBG Kew

Every cut a tiny improvement

Pruning a bonsai is the same as pruning a tree. Every cut you make should be a tiny improvement to the structure and health of the tree - so the tree gets better and better through the hundreds of tiny changes and choices you make over the years.

Bonsai tree in a white glasshouse with roots exposed
Bonsai with exposed roots

Remember your roots

Roots are an essential part of a bonsai’s physiology, but they can be somewhat overlooked – they are, after all, buried. Don’t let out of sight mean out of mind. The crown of the bonsai will reflect what the root system does. Many fine branching roots will create a mature crown to your tree, with a fine branch structure.

Black and white image of three tiny bonsai held in a hand
Tiny bonsai held in a hand © Paul Little, RBG Kew

It's not a pot, it’s a frame

Bonsai is all about the aesthetics. You don’t want to distract from your hard work with a pot so large, gaudy or unusual that you end up looking at the pot instead of at the tree. Try to choose a pot that harmonises with the look and feel of your tree, the way you’d choose a frame for a picture.

You can also try making a kokedama, or moss ball, using compost and sphagnum moss. Kokedama are easy to hang or display in a dish, and a great sustainable way to show off your plant without using a pot. Find out how to make a kokedama.

A drop of water on a leaf
Water drop © Unsplash

The art of watering

Getting the watering right is one of the most important parts of bonsai care. It's so important that bonsai apprentices in Japan aren't let loose with a hose or watering can until their fifth year.

Don't panic: if you only have a few bonsai trees, try dip watering. When the tree’s soil begins to look and feel dry, plunge the whole pot underwater: you might want to use an old washing-up bowl. Once thoroughly soaked, take the pot out and set it aside, slightly tilted to help the excess water drain away. Repeat the process when the tree starts to dry out again.

Pink blossom of bonsai Hall crabapple tree (Malus halliana)
Bonsai Hall crabapple tree (Malus halliana), Emma Chandler © RBG Kew

You don’t need special feed

Expensive ‘tailored’ feeds are unnecessary, and a waste of money!” says Richard.

Any standard commercially available houseplant or garden fertiliser will keep your bonsai happy: ideally something organic or seaweed-based. As long as the NPK (nitrogen, phosphorus, potassium) ratio is close to 5:5:5, your plant should be fine.

close up of a hand pouring fine red gravel onto a bonsai in a pot
Richard Kernick demonstrating akadama soil on bonsai

You do need special soil

On the other hand, specialised soil is a wise investment.

Richard's take: “The best type of soil for bonsai is called akadama and comes from Japan - but I’m experimenting with cheaper alternatives as it is very expensive, and importing it is not exactly environmentally friendly!

Akadama is made up of tiny grains of volcanic clay. Bonsai growers love it because it holds onto moisture and nutrients while still draining well. It’s often combined with other materials like sand to make a customised soil mix.

At Kew, Richard is currently experimenting with moler clay, a type of diatomaceous clay found in Denmark, which works in a similar way to akadama. You can often find diatomaceous earth available as cat litter – just make sure not to use clumping or scented cat litter on your plants.

A bonsai tree shot from a low angle, planted in a gravelly garden bed surrounded by other plans with brick walls in the background
Bonsai in garden bed in the nursery © RBG Kew

Give your tree a holiday

Sometimes bonsai get a bit tired of being in the same pot. Maybe a pest outbreak has weakened the tree, or a few missed waterings on an unexpectedly sunny day have left the bonsai feeling and looking stressed. Many of the trees in Kew's collection struggled after the pandemic, especially in the hot summer of 2020.

Richard's secret is that a change is as good as a rest for an unhappy bonsai.

"If I consider a tree to not be healthy enough to be displayed, I’ll occasionally give it a holiday for a year or two in a plastic crate, polystyrene box or even a flower bed: any temporary container that is a bit bigger than its usual pot. Once the tree is stronger and healthier, it will better withstand being put back into its old pot."

Three men cluster around a bonsai maple with bright red trees, pruning and examining the leaves

Remember: it's just a plant

It's easy to get wrapped up in the art of bonsai; it lends itself to careful concentration and focus. Amongst all the specialist feeds, tools, pots, soil and other bonsai paraphernalia, it’s occasionally worth taking a step back for a dose of perspective.

Richard's take: "Remember that you’re basically just looking after a pot plant."

Close up of red acer leaves on a bonsai, with a long shot of a small white glasshouse in the background featuring other bonsai trees
Kew Gardens bonsai house © RBG Kew

Don't forget to enjoy it

In Richard's words:

In the early days of working at Kew, I made the mistake of remarking to my Japanese bonsai tutor, Nobuyuki Kajiwara, about one of the trees: “It’ll be good when it’s finished”.

He looked at me slightly quizzically and responded:

"When it’s finished, it’ll be dead. Up until that point, it’s doing one of two things: getting better or getting worse. It’s your job to make sure it keeps getting better.”

In the West, we can be very fixated on goals. We delay gratification to some point in the future when we perceive something to be “good enough”. Take the time to enjoy your bonsai, whatever stage of the journey it’s on.

As the saying goes: The best time to plant a tree was ten years ago. The second-best time is today.


Two women gardening

Community and access learning at Kew

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