Wall Training for Frost Protection

A south-facing wall is one of the most valuable assets in a garden. The wall absorbs heat from the sun during the day and releases it slowly through the night, creating a microclimate that can be two to four degrees warmer than the open garden. Training plants against a warm wall is one of the oldest and most effective ways to grow borderline-hardy plants outdoors in climates they would not otherwise tolerate.

Why walls protect plants from frost

Walls act as thermal mass — they store solar energy during the day and radiate it back at night, slowing the rate at which temperature drops after sunset. On clear, calm nights when radiation frosts are most severe, this released heat can make the difference between a plant surviving and being damaged. The wall also provides physical shelter from cold winds, which significantly reduces wind chill and the desiccating effect of cold, drying winds on tender foliage. Plants trained flat against a wall are also less exposed than free-standing plants of the same species.

Best plants for south-facing walls

South-facing walls are ideal for frost-tender or borderline-hardy plants that need warmth to ripen wood and resist cold. Classic choices include trained fruit trees — peaches, nectarines, figs, and apricots all fruit far better against a south wall than in the open. Tender shrubs like Californian lilac (Ceanothus), myrtle, pittosporum, and the Chilean potato tree (Solanum crispum) can be grown as wall-trained specimens in positions where they would not survive in the open. Climbing roses against a south wall also flower earlier and longer than free-standing plants.

• Peaches and nectarines: need wall warmth to ripen fruit in cool climates.
• Figs: fruit best with maximum reflected heat.
• Ceanothus: borderline-hardy, thrives against warm walls.
• Climbing roses: earlier flowers and extended season.

North and east-facing walls

North-facing walls are cooler and shadier, which makes them suitable for shade-tolerant plants that benefit from the shelter without needing warmth — pyracantha, climbing hydrangea, and some shade-tolerant roses do well here. East-facing walls receive morning sun, which can cause problems for frost-sensitive plants in spring — frosted buds thawing rapidly in the morning sun suffer more damage than those that thaw slowly in shade. Avoid training the most frost-sensitive plants on east-facing walls.

Setting up wall training

Attach horizontal wires to the wall at 30–45cm intervals using vine eyes and tensioners, running the full width of the planting area. Train the main branches of the plant as a fan or espalier framework tied to these wires. Tie in new growth regularly during the growing season. Plants trained against walls dry out faster than those in open ground because the wall eave creates a rain shadow — check soil moisture regularly and water more freely than you would for the same plant in open ground.