The most commonly grown Mahonia are upright and tall but in fact there are many varieties with of different sizes although all tend to be fast growing. The group of Mahonia known as M. x media are all upright varieties, and illustrated below left is 'Charity' which has lovely yellow fragrant flowers. The upright varieties are the most common, but there are also a low growing varieties, Mahonia repens, which grows up to 30cms, illustrated in the image below right and can be used as ground cover.
The most popular varieties grown in UK gardens are:
Mahonia x media which grows up to 5m high 4 m wide and flowers from late autumn to early winter; good varieties are 'Charity', 'Winter sun' and 'Lionel Fortescue' and all are very hardy H4. These have large upright yellow, scented flowers. 'Charity' can be grown in a north facing spot which makes it a good shrub for a difficult growing area.
Mahonia fortunei smaller 1.2m high 1 m wide which flowers in the autumn
Mahonia aquifolium known as the Oregon Grape, image left is a smaller compact variety, up to 1.5 metres, very hardy and is spring flowering in March and April followed by blue black berries.
Recently the RHS have awarded Garden Merit (AGM) to Mahonia x media Underway which reaches up to 3m and has large erect spikes of fragrant yellow flowers in the winter.
Mahonia japonica is also hardy to H4, a mid sized shrub growing up to 2m.
A recent introduction is a red flowering Mahonia called Mahonia nitens 'Cabaret' which flowers in late summer and autumn.
When growing Mahonia you do not have to prune the shrub, but a light prune, from time to time after flowering, will trim the shrub into shape and remove any dead branches.
Mahonia look good under planted with snow drops and Hellebores to provide a mixed winter border. Suitable companion shrubs would be Berberis if making a thorny hedge, or Rhododendron, Azalea and Viburnum if planting a mixed shrub border.