Winter Protection

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While many plants, including those that do not originate from the UK, cope well with our winters, others have more difficulty and need a little attention if we are to enjoy them next year. This blog describes some of the techniques I use to get some of my more ‘tricky’ plants through our coldest season.

Frost can kill plants if the roots are frozen in the ground and unable to take up moisture, especially with evergreens where the foliage will still be losing it. I leave all the cutting down of perennials until early spring to afford some protection but also mulch the bases of particularly vulnerable plants with straw, fern fronds or even garden compost – melianthus major and hedychiums are among those to receive this treatment. If possible, this is put in place while the soil is damp but not saturated (although that won’t be possible this year after the wettest November on record). Very borderline hardy plants will also be wrapped with fleece for added protection.

Some plants can take low temperatures provided the roots are not sitting in saturated conditions. When planting these, I mix lots of horticultural grit into the surrounding soil and put more in the bottom of the planting hole. My banksia took -8C in its stride last winter because it was in a very sharply drained mix. Other plants, such as arisaemas and lobelia cardinalis, require moisture in the growing season but much drier conditions when the temperatures drop, coming from areas where most rainfall occurs in summer rather than winter. These are grown in pots stood on bricks around the edges of my pond and moved into a cold greenhouse for the winter. Here they receive no attention at all and are put back in the pond in spring without any hardening off and seem none the worse for this regime.

Some of the heucheras with orange leaves (such as Amber Waves) don’t relish cold, wet winters either; as mine is growing in a pot, it can be stood in a cold frame until next year.

Similarly, many alpines, coming from mountainous areas, will take cold weather but, being protected by a blanket of snow, do not have to deal with cold rain freezing in their crowns. Using some the bricks from the pond, I cover the vulnerable ones with sheets of glass which gives them the shelter they need to come up smiling again next spring.

I don’t grow many annuals but one grass that is not frost hardy is pennisteum setaceum ‘Rubrum’. The rootball is fairly compact so this can be dug out and potted up each autumn and overwintered indoors where it receives a weekly watering. In the spring, I cut back all the top growth, harden it off and, when all danger of frost is past and the weather in a warm phase, replant it back into a sunny border.

There are other plants which I know won’t take much frost but are not as obliging as the pennisetum so I am experimenting with a new method for them. When planted out, they are placed in a bottomless plastic pot, buried in the soil (the bottom is cut off so there is no hinderance to drainage during the growing season). Come autumn, they are dug up and because the roots are contained, there is minimal disturbance.

Now the pot can just be slid inside another of the same size and the whole thing brought inside for winter on a windowsill.

I hope this gives you some hints and ideas about successfully getting plants through what can be very testing times for them.

• 2 Dec, 2009
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