Not Always What They're Cracked Up To Be
by
This is when the cracks start to appear.
Well, perhaps not with the very first frosts, but as winter progresses, and the frosts become harder and more prolonged, your outdoor pots and containers will begin to feel the strain.
In this piece, I want to deal with two aspects of the effects of winter on outdoor, containerised plants.
First, let's consider the containers themselves, and their suitability for the winter elements. And secondly, the effects of harsh winter weather on containerised plants.
Already I'm scaring myself. I am now committed to a structured article instead of the usual meanderings. Can C in the P cope with such discipline?
Read on to find out.
Pots and containers
Now obviously, wood and plastic are fine. Well, not fine, exactly. Wood is fine. In fact, wood is a great insulator, and timber troughs or wooden half-barrels have my whole-hearted support. Mention plastic (imitation terracotta) and I immediately dive for the crucifix and the garlic. But to give credit where it's due, plastic will stand through the winter.
Our most desirable containers, however, are terracotta. And the main producers of terracotta pots are around the Med, and Indonesia. These are often labelled "Frost Resistant", which may well be true in the country of origin, but rarely will they survive -25 degrees in Aviemore. (Or indeed places of similar latitude, like Moscow, and the various parts of Canada inhabited by occasional, and very welcome, visitors to this column.)
Others are labelled "Frostproof", and these you must seek out. Not necessarily because they are, but because "proof" is a clearly defined description, and you have a comeback!
I have always subscribed to the view that you should buy plants which have been raised farther north than where you're going to plant them. They're bound to be hardy enough.
I am tempted to suggest that the same should apply to terracotta pots. Though I realise this may give rise to a sourcing dilemma for my friends in Nova Scotia and Alaska.
(Sourcing dilemma or business opportunity? If the latter, a small commission would be appreciated!)
Back to topic, and to summary:-
If you want containers which will stay outdoors all year round, and you are subject to winter frosts, buy terracotta which is sold as frostproof. Do NOT trust those described as Frost Resistant.
If in doubt, buy timber planters. But only if you can be sure the wood is from a sustainable source. Otherwise you'll have me to answer to.
If you hate terracotta and timber, you probably have plastic gnomes in your garden. So buy plastic.
But if you email me with questions like "How do I care for my plastic pot over winter?", be not surprised by the expletives in the reply. (And you will get one, I promise!)
And finally, for terracotta lovers, a wee tip.
Pots crack when they have absorbed water, and the water freezes and expands. Simple enough, and hardly rocket science.
Ensure the pot does not have too much water to absorb by raising it off the ground, and eliminating any impediment to drainage.
Use pot feet, or a few small flat stones, or a couple of short wooden battens, or even a shovel-full of gravel. Use anything you like, but make sure that the base of your pot and terra firma are at least half an inch apart. Thus your pot should not become waterlogged, and your cracking problems should be minimised.
The plants therein
Mother Earth is a great insulator against frost. That's why we have herbaceous perennials which die down at the end of the season, then burst forth again in spring.
Though the topgrowth cannot withstand winter temperatures, the roots are well below ground and out of harm's way.
Not so with plants in containers, and the most common reason for failure of permanent containerised plants is freezing of the roots.
For a shrub or climber, planted in a pot, which is intended to remain there for many years, there are two basics.
First, it should be planted in a soil or loam based compost (a John Innes or home-made equivalent), rather than a peat based one.
And second, aim for a container 60cm diameter and 35-40cm deep as a minimum. Bigger is better, as far as frost-proofing is concerned.
And if you live in an area prone to hard winter frosts, try lining the inside of your container with thin polystyrene, before you fill with the growing medium.
Every little helps.
And likewise, re-arrange your pots before winter, if you can, bringing them together in groups. They will insulate each other.
And if all else fails, and you still worry about the cracking potential, wrap your pots in bubble-wrap for the worst on the winter.
Not a pretty sight, granted, but it helps greatly.
We also have a friendly discussion forum. Try our Clark in the Park board to discuss gardening related subjects, share gardening info, or ask a question. You'll need to register to join in but it's free and it only takes a minute.
Post to del.icio.us
