I’m wondering when is the best time to prune my Oregon grapeholly? It is a standard-size Mahonia, not a compact variety. It’s so pretty in bloom, but it needs trimming – if I do it now I’ll lose all the berries. If I trim it in the fall, will I lose the spring blooms? I hesitate to prune in fall because of the browning that occurs over the winter, which already takes a fair amount of leaves. Please help!
Sometimes in gardening, as in life, we find ourselves between a rock and a hard place. So it is in deciding when to prune your Oregon grapeholly (Mahonia aquifolium). As you’ve discovered, cut back this evergreen ornamental shrub in early spring and the slightly-fragrant, pyramidal-shaped cluster of bright yellow flowers won’t emerge during their typical April to May blooming time. Prune this shrub in early summer and there won’t be any of the bird-attracting, grape-bunched, chick pea-sized, blue-black berries in late July.
You must, however, prune to keep this vigorous-growing ornamental (it can reach nine feet) looking tidy. If you’re willing to sacrifice the flowers or the berries for a season, you can hard prune any time of the year, except early autumn. If you prune in September or later, the new growth that will be stimulated may not harden off before the killing winter cold. On the other hand, light pruning (cutting back one stem in three) in early summer will preserve most of the flowers and/or berries.
In terms of cultivation, if many of the lustrous green, leathery leaves die during the winter, perhaps your Oregon grapeholly needs to be moved to a different site. Hardy to zone 4, this native of the Pacific Northwest likes moist, well-drained, acid soil in a protected location; it doesn’t like exposure to excessive heat, dry soil, and desiccating winds.