The Cool Temperate Garden

Frost kills plants. Less than 10 per cent of plant species are resistant to it, yet gardeners have come to accept frost as a fact of life, working their plans around it with stoic resignation.

Frost has such an overwhelming influence that if only one climatic map appears in a garden book, it is that of the "hardiness zones". Such a map indicates the plants that can be grown outside without protection. As a result, we speak of "frost-hardy" and "frost-tender" plants.

The minimalist in a cold climate will grow fully hardy plants. Although the growing season may be short, plant materials can be harvested and stored.
In winter, even hardy species become dormant, leaving little to he had directly, except timber, fuelwood, and roots.

Perhaps it is surprising that humans—originally a tropical species—should ever have bothered with the cool temperate parts of the Earth. Only with the help of animals did they get through the winter, the more so in the polar regions. From the point of view of environmental sustainahility, the hunting/herding strategics of the Inuit, Lapps, or Mongols are admirable, but are not possible in the garden!

The determined minimalist will look out for edible weeds that grow in the winter and for perennials that give a spring crop earlier than their delicate annual counterparts. One common northern hemisphere weed that defies extreme cold and is always ready to be picked in the middle of winter is the hairy bittercress, Cardatuine hirsttta. Despite its name this plant tastes like watercress and is available with no effort bar the picking. Another is sheep's sorrel, Rurnex acetosella. Of the perennials, Good King Henry sprouts before any spinach, while the tree onion may be giving juicy greens in late winter.

Another easily harvested cold climate product is sap, which rises in early spring. You can tap sap by drilling a shallow hole in a tree trunk, inserting a tube into the hole, and collecting the runoff in a bucket or tub. Though maple is the most famous, birch sap is the source of the earliest and most ferocious of all the wild wines.

Improving productivity

Like gardens in other extreme climates, those with a severe winter and short growing season need substantial modifications to improve productivity; nearly all these modifications increase temperature. As in other cases, the strategy is to try and modify the overall garden (and if possible, the house) climate with little cost and effort, while concentrating the more expensive or time-consuming preparations on the most useful crops or garden products.

In cold climates, it is worth considering whether the garden should really concentrate on reducing fuel bills instead of growing food. The simplest way to reduce heat loss and wind chill is to clothe the house with a heavy evergreen vine, such as ivy, that traps a layer of air next to the wall. Erect windbreaks, at least on the side of prevailing winter winds, but also on the poleward side.

A horseshoe windbreak around the house is best since it leaves the sunward side open to the low winter sun, which in some climates can substantially reduce the heating load. Trees planted on the sunward side of the house should be deciduous in order to let light through the bare canopy during the winter.

Valuable methods of lengthening the growing season include cloches, cold frames, and greenhouses for productive crops. A greenhouse is a place that benefits many other activities in a cold climate—it can even be a sanctuary.

The cheapest form of greenhouse is the polytunnel, an ugly polythene structure with great potential on account of its size. It can act as a workshop, garage, playspace, laundry, picnic area, store for compost, outdoor lavatory, plunge pool, bathhouse, dry storage, or toolshed.

Cool climate sanctuary

The main priority of a cool-temperate or a cold-­climate sanctuary is warmth. In cloudy, oceanic climates even the summers can rarely be described as hot. But many climates that experience severe winters are continental and therefore have hot summers. Hence, the sanctuary needs to be flexible enough to create cool conditions in summer and warm conditions in winter.
A solution for gardens with mixed requirements is a series of covered zones centred on the house. A combined conservatory–verandah built on to the sunward wall at the front of the house, to the east if you have a choice, is a priority. Adjoining the conservatory, inside the house, a small antechamber with a view provides the sanctuary during the coldest weather.

For several months of the year, the conservatory will be at a comfortable temperature in the day through solar gain and incidental heat from the house. In really hot weather, a covered, open verandah surrounded by vines or deciduous shade trees provides the required coolness.

In cool, oceanic climates, the conservatory is best placed on the east of the house so that it warms up quickly. In continental climates, the conservatory is better on the west, with the verandah decorated with deciduous vines.

The unheated greenhouse has a number of features that help moderate temperature extremes in cool climates.

An internal pool and massive insulated stone walls on the poleward side absorb heat and release it slowly during the night.

A raised growing bed, during the colder parts of the year, is given additional protection with glass frames. In winter, ground heat conducted to the empty space below the bed allows the growth of tender crops. In spring, it is used as a hotbed, with compost heat permitting the rapid germination of seedlings in trays. In summer, the bed is perfect for warm climate crops, such as melons and egg plants.

Even in high latitudes, tropical crops, such as the bananas crown in a geothermally heated greenhouse in Iceland, can be viable so long as sufficient heat is available. The long hours of daylight can give good, rapid yields.