Grow­ing Ja­panese ac­ers for ex­cep­tional au­tumn colour

Get the ex­pert’s tips on grow­ing these much sought-after trees for ace au­tumn colour

Garden News (UK) - - Contents - Words Neil Ken­ney, RHS gold medal-win­ning acer spe­cial­ist

Here we sim­plify the mys­ter­ies of grow­ing maples and ex­plode the myths that sur­round them, and pro­vide you with all you need to suc­cess­fully grow Ja­panese maples (ac­ers) .

We hope you’ll ex­plore the beauty of these grace­ful trees, with their stun­ning colours and ma­jes­tic forms, by plant­ing one or maybe two!

Are they hardy?

apanese maples are mis­un­der­stood. Peo­ple be­lieve 'they don’t like the wind’ or ‘they don’t like the sun’, yet maples have lived with wind and sun for thou­sands of years, and if they weren’t com­pat­i­ble with these el­e­ments they wouldn’t sur­vive to be the beau­ti­ful trees they are to­day.

In the win­ter of 2010/2011, the UK ex­pe­ri­enced tem­per­a­tures of -20C (-4F), and Ja­panese maples were one plant that came back fight­ing. Any that didn’t sur­vive had other un­der­ly­ing prob­lems.

How­ever, when maples break leaf in spring they can be sus­cep­ti­ble to air frosts in late April and May. These can burn the leaves, show­ing a bleach-splat­tered ef­fect. This won’t kill the plant, but if an air frost is fore­cast and your maple’s in a pot, move it tem­po­rar­ily to the green­house.

Grow­ing Ja­panese maples in a pot

It’s im­por­tant to re­mem­ber not to choose too large a pot or con­tainer. Don’t use ter­ra­cotta pots, as too much mois­ture is lost through the wall of the pot and the tree will de­hy­drate, caus­ing brown leaf tips and edges. Al­ways use glazed stone/ce­ramic or plas­tic with good drainage holes. ● If you’re pot­ting on from a one litre pot, only move up to a max­i­mum of a 2-litre pot, which will be suf­fi­cient for one season’s growth. Then from a two litre to three litre, and three litre to five litre – and from then on move onto a con­tainer that's just big enough to get the flat of your hand down be­tween the root­ball and the side of the new pot. ● Re­pot in spring just as the leaves are about to break, or in Au­gust when top growth is start­ing to slow down. Pot­ting on can be car­ried out mid­sea­son, but may cause brown­ing of the leaves as the roots adapt them­selves to the en­vi­ron­ment of the new com­post. Don’t re­pot Ja­panese maples in au­tumn when the leaves have dropped as they’ll make very lit­tle root, and the ex­ist­ing roots could be­come dam­aged and rot away. ● If you’re us­ing a tall planter, don’t fill the whole depth of the pot with com­post as this will cause the root­ball to rot over time. The bot­tom three­quar­ters of the planter should be filled with coarse stone or bricks for sta­bil­ity and only the top quar­ter should be filled with well-drained, multi-pur­pose com­post. ● In pots they need feed­ing through their grow­ing season. Be­tween May and July we use Mir­a­cle Gro liq­uid feed once a month. From Au­gust un­til the end of Septem­ber use tomato feed, which will har­den off soft growth ready for win­ter.

Over­win­ter­ing

The big­gest threat to pot­ted maples is be­ing left out in win­ter and be­ing al­lowed to get wa­ter­logged; this in turn rots the fine root sys­tem, which en­ables them to grow suc­cess­fully in con­tain­ers in the first place.

To avoid this hap­pen­ing, as soon as your maple has dropped its leaves in au­tumn, the tree and con­tainer should be moved to a po­si­tion shel­tered from rain. This must still be out­doors with free air move­ment all around. Don’t wrap up your maple as this will cause bac­te­ria to form. Re­move any dishes that the pot’s stand­ing in, to avoid col­lect­ing wa­ter. Pots should be raised off the ground to stop wa­ter be­ing drawn up into the pot. Don’t wa­ter your maple again un­til the buds be­gin to break in the spring, and only very spar­ingly to start, in­creas­ing as the leaves un­fold and the weather improves. Pro­tect from late frosts.

Maples don't need large pots – they can be planted in shal­low con­tain­ers – but avoid ter­raco a as these lose mois­ture

Ja­panese maples won't put down deep roots in the gar­den and stay com­pact, too

When po ing ac­ers into tall pots, fill three quar­ters with drainage ma­te­rial and the rest with multi-pur­pose com­post

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