By Kathryn Pankowski
The most common question at this fall’s plant swap was “Will this survive winter on my balcony?” So, since you asked, here’s how to help a potted plant live to see the spring.
The first step is to make sure you know what your plant is. A rose by any other name might smell as sweet, but it’s much harder to look up on the internet, a point which seems to have escaped Shakespeare. If you need help, there are lots of plant ID apps available, and they’re getting better each year. Or you can post a photo on the UBC Botanical Garden plant ID forum. Or take a photo and/or leaf to the Master Gardeners next time they hold a clinic at the Central Branch of the library.
Once you know a plant’s scientific name, you can look up its hardiness rating, which will tell you the coldest climate zone in which it will (theoretically) survive without special cosseting – but (here’s the tricky bit) those numbers refer to plants in the ground. Plants in pots are much more vulnerable to cold.
Victoria, on average, is classed as zone 8b. Generally speaking, plants rated as hardy up to zone 7b should be fine outdoors in a planter box or half barrel, and plants rated up to 6b should survive outdoors in pots without any special cold-protection measures.
But Victoria is a city of microclimates. If you have a sunny south-facing balcony with a glass railing, you may have zone 9 conditions, while a north-facing balcony below ground level may be a ‘frost pocket’, catching colder air as it sinks. You’ll have to adjust your expectations to your circumstances.
Wet can be as big a hazard as cold. Turn drip saucers over, so plants aren’t standing in water after heavy rains. Check that ornamental cachepots aren’t filling up with water. Move dry-loving plants under eaves or close to the building so they get less rain on them.
And what about the plants that are borderline hardy, the ones where you know you might be taking a bit of risk? Put the most tender outside plants in the warmest or most sheltered spots you have. Often, that’s right up against the glass door onto your balcony, where heat escapes from the building. If you have a number of small pots, try grouping them closely together, with the most cold-vulnerable ones in the middle.
If the forecast predicts more cold than your plants can tolerate, emergency action is required. You can try draping an old sheet or horticultural fleece over the plants for a little extra protection. Or, if you have a little advance warning, protect them with a mini temporary greenhouse: a cloche, made from a plastic milk jug with the bottom cut off, will fit over a small plant, or you pop a group of plants into a mini cold frame made from a clear plastic storage box. Larger plants and planters can be protected by a framework of stakes with a clear plastic drop cloth draped over it and taped at the bottom. If these little ‘mini-greenhouses’ are in the sun during the day, they will raise the night temperature by several degrees, which is probably all you need to get your plants safely through few days of cold.
Or, if things get really dire, you can bring any particularly precious or vulnerable plants inside. The bathtub makes a handy overnight evacuation shelter – just remember to have your own shower first.
Neighbourhood Garden News
A group of volunteers has been working away on a proposal for making a James Bay berry patch on the traffic calming features at the north ends of Montreal and Pendray Streets. We now have some preliminary ideas and are discussing them with the immediate neighbours; we hope to have a proposal ready to show the ‘hood early in the new year.
Kathryn Pankowski is the James Bay Neighbourhood Association Neighbourhood Gardening Advocate: she can be reached at firstname.lastname@example.org. The JBNA would like to acknowledge the financial support of the City of Victoria for this initiative.