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Kalopanax - Growing Guide
Growing Kalopanax septemlobus (Syn. Kalopanax pictus)
The Castor Aralia or Prickly Castor Oil Tree
This is an Asiatic genus of one species of tree which is now being more widely grown for its attractive foliage and superb yellow autumn colour. One can readily put up with its many juvenile spines or prickles for a few years as this tree is very quick growing and the spines disappear from the trunk and older branches as they mature.
The mature and Cornish record tree at Caerhays was planted in 1991 and is 30-40ft tall today with a girth of around 3.5ft. There is every reason to suppose that it has some way to grow yet. It has an attractive spreading habit, grows in full sun and needs plenty of room to spread into.
The leaves are up to 14in across with five to seven lobes. The flowers appear in July or August in huge umbel-like panicles which are 8-12in across and composed of small white flowers whose scent is not entirely attractive. Thereafter the umbels exhibit rounded blue black fruits which fall to the ground in autumn after gales.
In Cornwall, where few trees readily produce decent autumn colour in our wet and seldom cold conditions, this is an exception. The leaves start to turn yellow in early October and fall in mid November a bit before other native species have started to turn and drop. One of the great sights in the autumn season to rival Cladastris.
Kalopanax can be germinated fairly easily in the cold frame in containers. Green or fresher new growth cuttings are more difficult to root or so we have found.