PLANTS NEED SHELTER FROM COLD
As cold weather approaches, it’s time to think about the patio containers out on our decks and situated way up on the balconies of highrise apartments. There are two concerns: one for the actual pots, especially if they are ceramic, and the other is for the plants, particularly if they are hardy annuals or more tender shrubs or perennials. In smaller apartments and condos, there isn’t a lot of room inside to store plants when the temperature drops well below freezing.
So how can you protect these plants like canna lilies, fuchsias, dahlia tubers, abutilons and hardier outdoor palms? Also at risk, when planted in containers, are hardier plants like Japanese maples, camellias, rhododendrons and other shrubs as their roots could be more exposed to heavy freezing. Location can make quite a difference. If the patio is facing south or west, usually it is less affected by colder winter winds and the plants can even benefit somewhat from the little winter sun we get. It is a more difficult situation for plants situated on the north or east side of a building where they not only miss out on the waning sun, but they are also exposed to colder winter winds. Wind chill adds another layer of concern.
First, let’s look at containers. As a rule, the larger the container the better because of the critical mass of soil it provides. Also important is the soil used in the containers — it must be porous and drain well.
Good drainage means less moisture to freeze and expand the soil — a process that can cause poorly fired ceramic pots to break. Frost-proof ceramics are more expensive, but they are generally thicker and fired longer and at higher temperatures, so they are able to withstand the expansion of frozen, wet soil.
Plastic containers usually have more flexibility, but can sometimes crack. I find resin pots to be much better as they are more resilient to frost. Metal and fibreglass pots are fairly good, too.
Whatever the container, goodsized, open drain holes on the bottom of the pot are essential to allow for the flushing of excess water. Loosely covering the drain holes with large stones or with pieces of broken crockery helps to hold in the soil while keeping the drain holes open and functioning.
On the West Coast, with all the winter rains, it’s wise to move your containers under an eave to minimize the amount of moisture in the soil. Remember, however, that containers placed under eaves will need to be checked regularly to ensure they don’t dry out too much. To prevent desiccation, your containers will still need to be watered periodically. No matter where your pots are situated, group them all together at this time of year so they help shelter each other.
The main issue is going to be the degree of coldness we experience this winter. On the islands and the West Coast, the worst-case scenario is usually a few degrees of frost, which is manageable. More inland areas, such as the eastern Fraser Valley, the Interior and places further north where wind chills of -20 C or lower are not uncommon, patio containers need greater protection. In areas with milder temperatures, such as Zone 7 and higher (lowest temperature of -15 C), generally all that is required during colder periods is a protective wrapping of any good insulating material. The nursery industry uses several products like N-Sulate, a white cloth similar to Reemay floating row covers. N-Sulate provides up to 10 degrees of added protection.
Many folks still use burlap to wrap their plants and containers, but although it may diffuse the wind, it offers no real protective frost value. N-Sulate is relatively inexpensive and is generally sold in garden stores as a “frost blanket.” It can be reused year after year if dried and stored properly.
In colder regions, like zones 5 and 6 (lowest temperatures of -26 C and -20 C, respectively), insulating materials like N-Sulate can still be fairly effective, but you may need to wrap it around your pots several times.
In worst-case situations, use household insulation with an R20 rating to wrap your pots and then cover them with plastic to keep them dry and to maintain the insulating value. This type of insulation will protect both your containers and the roots of your plants as well as any bulbs planted in the pots.
The hardiness of the plants in your containers is also a key factor. Most tender Zone 9 plants, like some tougher tropicals, will not tolerate any frost, so you will have to bring them inside for the duration of the cold spell. If you live in an apartment, even putting them in your storage area, if there is one, will help.
Zone 7 plants like Spanish lavender and Zone 8 plants like phormium are also tender and can take only a light frost. However, by giving them a little protection with N-Sulate, they should be fine.
I find it very effective and more attractive to insert three strong stakes deep in each pot to create a tripod-like framework around which I wrap both the plants and the pot with insulating material.
In the case of extremely cold temperatures, take a large box, ideally a wooden one, and fill it with household insulating material. Then set your pot inside, topping it with a layer of N-Sulate and a covering of plastic. With this kind of protection, your container should be fine.
If you can’t find a supplier of frost blankets, then use either Reemay cloth or burlap, but be sure to wrap your containers with several layers.
More and more of us are using attractive containers of plants, cut greens and trees to decorate our patios for winter. It really is worth the effort to help them through the coldest outflow winds by giving them some protection for the few days when the temperature is at its worst.
After we have a snowfall, which will conveniently provide another insulating layer, or when the temperature begins to warm up, all should be well.
Once the temperature is on the rise, check the soil in the containers for moisture and spritz the foliage of your plants to mitigate any damage. Mist and water all your cut greens to rehydrate them as they may have dried out.