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Mahonia - Growing Guide
Mahonia - Growing guide
The exciting thing about these (mainly) tough evergreen plants with shiny dark green pinnate foliage and spines only on the leaf edges (rather than the stems) is that, in recent decades, Roy Lancaster and others have discovered quite a number of new Himalayan species previously unknown in cultivation which we are starting to grow at Burncoose and hope to offer to you in the coming years. This has all caused much excitement and confusion amongst taxonomists who have had to reclassify and rename some species within this genus. These botanical rows and arguments have been ongoing for some time as to whether Mahonia are related to Berberis. The name mahonia commemorates Bernard M’Mahon, an American horticulturalist, who died in 1816.
Mahonias are grown for their handsome foliage. The new growth in some species is attractive too and often purplish-red or orange-red when young. However, it is their handsome racemes or panicles of cup shaped yellow flowers followed by purple or black berries which is the key attraction especially as, in many species and forms, this occurs outside the main flowering season in autumn and winter.
All the mahonias which we currently offer are fully frost hardy and have a variety of uses in the garden. Low growing species can be used as groundcover, taller, more upright species can fill the back of the border and larger growing species and varieties can be used as freestanding woodland garden plants. The spiny leaves make a good deterrent to intruders in a town garden and some mahonia species can make a good hedge which responds well to pruning and clipping.
Mahonias prefer full or partial shade. In full sun the foliage may discolour and turn yellowish unless the soil remains moist through summer.
To avoid too lengthy a list of different species it is easiest to split the genus into three types of flower form:
Upright clustered flower panicles (typically less than 4in long)
Mahonia aquifolium (Oregon grape) varieties (‘Apollo’ and ‘Smaragd’) are open suckering shrubs with 12in green leaves and nine ovate spiny leaflets which turn red-purple in winter. Flower racemes are 3in long in spring followed by blue-black berries.
Mahonia fortunei is an upright shrub growing to 4 or 5ft with 8in long leaves which have up to 13 leaflets. The upright flower racemes are 3in long and appear in early to mid autumn followed by dark blue berries.
Mahonia nervosa is a dwarf suckering shrub with 24in dark green leaves which have up to 23 leaflets which turn red-purple in winter. The flowers are in yellow racemes of up to 8in in length in late spring and early summer. Blue-black berries.
Mahonia x wagneri is a small upright shrub with 8in long leaves with seven to eleven dark green leaflets. The flowers are borne in spring in dense racemes 3in long and followed by rounded blue-black berries with a white indumentum.
Arching, spreading, flower panicles
Mahonia japonica forms an erect but spreading shrub and there has been much recent debate about the true form of the real M. japonica. It has stout branches and 18in long leaves with up to 19 ovate-lance shaped leaflets. The flowers are highly fragrant and can appear with us in December, January or February. They are pale yellow in arching, then spreading, racemes up to 10in long. The berries are blue purple and we do grow this species in full sun.
Mahonia japonica ‘Bealei’ has light blue-green leaves and shorter flower racemes.
Upright then spreading flower panicles (up to 18in long)
Mahonia lomariifolia is an erect shrub growing to around 10ft tall with chubby stems and huge distinctive 24in long pinnate leaves with up to 41 sharply toothed leaflets. The flowers are fragrant and up to 8in long from late autumn on into winter. Blue-black berries.
Mahonia x media varieties (‘Charity’, ‘Winter Sun’ and ‘Lionel Fortescue’) are hybrids between M. japonica and M. lomariifolia. They are generally regarded as the best flowering varieties and the very easiest to grow to maturity. In these forms the leaves are up to 18in long with 17 to 21 leaflets. The flowers are bright yellow or lemon yellow and at least a foot or more long in racemes which start upright and then spread more widely. They appear in late autumn to late winter and usually brighten up our Christmas displays in our sales area.
Recently we have added to our catalogue the popular Mahonia eurybracteata ‘Soft Caress’ which was RHS Chelsea Plant of the Year in 2013 although not in flower at that time. The flowers are a gentle yellow and, unusually, the leaves have no spines.
Hopefully to follow shortly as new introductions by us are Mahonia napaulensis, M. gracilipes and M. nitens.
Images to follow [Lots of pictures on blog plus we could add pictures of new varieties not yet in catalogue]