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Many of our customers buy topiary plants (and hedging plants) to grow in containers, one frequently asked question is how large does the pot that I plant them into need to be?

For topiary there are 2 answers…..

The first and best answer if you want to treat your topiary plants as a long-term investment instead of expendable, short term decoration, is to choose a container that is at least 20cm wider than the pot it is in (so allowing for at least 5cm all around the root ball when you replant it). This way the plants should give you many years of service, especially if they are potted on again every few years….and eventually transferred into the open garden when they eventually get too big.

If you buy a topiary plant from us in a 10 litre pot, that pot has a diameter of about 28cm, so the plant will need to go into a new pot of at least 38cm –  which is approx. 30 litres volume.

So, the rule of thumb is that the new pot ideally should hold at least 3 times the volume of compost so that the plant can grow and develop properly. (4x would be even better!)

The best compost for long term topiary plants is a soil based one such as John Innes No 3. It won’t dry out and shrink like soil-less compost and will hold onto nutrients more effectively which is important because topiary plants in containers will need regular feeding to keep them looking their best.

The second answer is you can use any container that’s just about large enough to accommodate the root ball, and that can make for some very attractive ‘window dressing’. We don’t recommend this approach unless you are prepared to replace the plants frequently (the small volume of soil will not be able to buffer for dry spells, or someone forgetting to water them in hot weather – leaving the plant very vulnerable. Also, they won’t have fresh soil for the roots to develop into long term. For that reason, we don’t guarantee topiary plants that have been transferred (‘transferred’ is a more appropriate word than planted!) into small containers like this). Topiary treated this way will realistically need to be replaced once or twice a year to keep the containers looking tip top. Sometimes space is limited and it’s the way things must be, for example the window boxes outside prestigious hotels are usually ‘overplanted’ but they look magnificent. The flip side is that part or all of the display needs to be replaced regularly.

One final word on planting topiary – almost all Box, Yew and Japanese Holly topiary is grown in the soil in the nursery fields – these plants simply will not develop into the required shapes in the restriction of a pot, they need a free root run. Once they are ready the plants are carefully root balled and potted to keep them fresh and ready for sale. So often when you remove the plant from the pot that we supply it in – if the plant was prepared for sale recently then the roots will not have re-grown yet. There will be a root ball in the centre and some loose potting compost around it. It may seem a little disconcerting, but its fine – all topiary whether from us or the local Garden Centre is likely to be the same. Like any new plant, just keep it well watered while they establish, and add some rootgrow when you plant to speed up the growth of those new roots!

A few words about planting hedges in containers

Our first advice is always this…..dont do it!

While this isn’t something that we recommend, sometimes screening is needed but there is no soil to plant in – just hard paving or concrete. If growing a screen or hedge in containers is the only option, our advice mirrors that for topiary – the pot or trough should have a bare minimum of 5cm clearance all round the root ball if the plants are to survive for any amount of time.

As another rough guide, if you buy hedging plants in 10 litre pots (28cm diameter) then the trough should be a minimum of 38cm diameter and at least as deep.

If we round that up just a touch to keep the sums simple, then a 1metre long trough would need to be at least 40cm wide x 40cm deep (x100cm long) which would hold 160 litres of the same John Innes compost that we recommend for the topiary.

Full of soil and plants and freshly watered, each trough could easily weigh up to 250Kg (quarter of a tonne), far too heavy to move without machinery if that was needed, on the plus side it would be less likely to get blown over in strong winds!

Even with a decent amount of soil for the plants to grow in – it would still be quite easy for the hedge to suffer (or even die) if watering was neglected for a few days in hot summer weather. Potted evergreen hedges can dry out even in the middle of winter if there are cold, drying winds. (For this reason, we do not guarantee any species of hedging plants that have been planted into containers).

We aren’t trying to put you off the idea completely – just to state that growing a good-sized living screen in a container is a big undertaking to begin with, much bigger than you might think at first. And then comes with the continuous ongoing responsibility of watering it. It’s worth considering every other option first and only opting for containerised screening if every other option has been excluded. Digging up concrete or paving might even be cheaper and less hassle in the long run, and it will certainly give better results if the hedge is growing in the soil!

About the Author

Morris Hankinson is the founder and MD of Hopes Grove Nurseries, the largest grower-retailer of hedging plants in the country. He started the business in July 1992, the day after completing his last exam of a BSc. Horticulture course at Writtle College in Essex. Morris has had a fascination and love of growing things since childhood when he was a keen exhibitor at his local Horticultural Society. Over the years the nursery has developed from a one person operation to an employer of 25 staff and so his interest is put to very good use, keeping an experienced eye on all operations across the 125 acres of nursery production.

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