Given adequate space and light, cranberries won’t require much maintenance. However, that often isn’t the case, and I usually have to reinvigorate these plants as I encounter them.
Pruning Time: Late winter is ideal. I prefer to prune these plants in dormancy so I can see what I’m doing. I use one of two methods: 1) Reinvigoration – I remove old, woody, overgrown stems that are crossing throughout the canopy. As well, I remove as much deadwood as is feasible (it can get pretty messy in there!). After pruning, the shrub has a structure that “makes sense”, with evenly spaced stems flowing up and out to the growing tips; 2) Renovation – In small areas, like over-planted shrub beds, it is useful to renovate woody suckering plants to grade, in rotation. For instance, one year I might renovate all the potentillas and favour the cranberries, and the next year I might renovate the cranberries. It is a drastic pruning method that is similar to coppicing. I like using this technique to control the height and width of the shrubs, and to ensure that I always have the most healthy-looking new growth. Once again, given enough space, this would not be the technique of choice.
Hedging: I have been able to make acceptable hedges out of the compact forms of European cranberry. Use hand shears as you would for any hedge, after the spring growth flush. Avoid shearing if the plant has powdery mildew on the leaves. I wouldn’t recommend this plant as a formal hedge for the main reason that if we get an extreme winter, you may get patchy die-back, ruining the look of the hedge.
Diseases: Powdery mildew can be a problem on the compact forms, during a warm, wet summer. Generally, the cranberries are insect and disease resistant.
Renovation: As noted, old or overgrown plants can be renovated, during dormancy, to a few inches above grade. Healthy new growth will emerge and reach a height of about 2-3’ in the first growing season. This can be further reinvigorated and trained in successive seasons.
Irrigation & Fertilization: As with most plants, cranberry prefers moist, well-drained soil. I provide a mulched area under the plant to protect the roots and retain soil moisture during extended hot weather, and to decrease watering requirements. These are reasonable drought-tolerant plants.
(c) 2011 Shane LePage, Wild Rose Tree Service, Red Deer, AB