Question
I’ve planted a dappled willow (Salix integra ‘Hakuro Nishiki’). Should I prune it in autumn? How much fertilizer should I give it, and does it need mulch and winter cover?
Answer
It’s not wise to prune this plant in autumn: this will expose it more to the cold, increasing the risk of frost and branch damage, and it may then suffer winter injuries. It’s best to prune in spring, when the risk of frost has passed. This willow is usually treated as a pruning shrub, i.e. cut back to 8-10 cm (3-4 inches) from the ground each year to maintain a shrub-like habit. Otherwise, it will become a small, sickly tree, losing its density. It is cut back a 2nd time in mid-summer, but more lightly, when its variegated leaves turn green, to stimulate colorful regrowth.
Beware of nitrogen-rich fertilizers with this plant: they stimulate dazzling growth… but you lose the beautiful pink and white colors characteristic of its foliage. Prefer a slow-dissolving organic fertilizer with a first number no higher than 7 or 8, or simply compost. Mulch will be very useful, as it appreciates moist soil, and mulch helps protect against drought. No winter protection is needed, as it is hardy in canadian hardiness zone 4b and you live in this zone.
Extending the Life of Your Spotted Willow
Finally, to prolong the life and vigor of your spotted willow, be sure to plant it in a sunny or partially shaded location, as it particularly appreciates light to retain its bright, vibrant colors. By favouring an environment that meets its light and moisture requirements, and using organic mulch, you’ll get the most out of its variegated foliage and compact growth, even without excessive maintenance.
Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This article was originally published in Le Soleil on November 21, 2005.
Why would autumn pruning be a consideration anyway? Although I am not concerned about frost (since the climate here is much milder than the harsh climates that it is native to), I would not want to prune it early and potentially stimulate any bit of growth during warm autumn weather that could actually be vulnerable to cold and rainy winter weather, with or without frost. I mean, the species is naturally dormant for winter so that it can be safe through frost. Premature pruning can stimulate premature growth, even if just minimally so, and such new growth could actually be vulnerable to frost, even here. Although I prefer to prune during the coldest part of winter, and am confident that this willow would stay dormant for the rest of winter afterward, I know that it is best to prune at the end of winter. That is because warm weather that can stimulate vascular activity and growth can happen at any time here, even in the middle of winter. In this climate, where winter is mild, I would not want to wait until spring, because, by that time, new growth is already emerging, and I would not want to damage it.