Canna 'Cannova'

Half-hardy Plants

This is a very broad category, but generally any plant which will grow happily and benefit from being outdoors, from typically after the last hard frosts until the first hard autumn frosts, and will give interest to the summer garden in the British Isles.  

Across the British Isles there is a huge range of climates and weather within which different areas and gardens experience an equally large range of microclimates.

December 2022 will be remembered as a wake-up call for all of us growing half-hardy and borderline hardy plants.

Think ahead to winter, and be prepared to either,

• Take cuttings and be prepared to lose the mother plant
• Prepare plants for winter, in September – dry off (many plants will be better on the dry side rather than wet). From late September onwards light or no watering, if in doubt don’t. That’s tricky if we get a late warm spell,  but remember that after the equinox (around 20^th September) the nights are longer than the days so night time conditions will have more effect than daytime. With very warm sunny days possible around this time it’s all too easy to water too liberally – if a cold, wet, dull spell then follows it’s unlikely the compost will dry out again and plants may suffer. There is evidence that by reducing watering the sap in the plant’s leaves and stems becomes more concentrated so delaying and reducing frost damage.
• Lift onto bricks to ensure good drainage, move under the shelter of house, hedge, or make a sturdy wind proof shelter over plants like Agaves to keep the rain off them.
• Feed with high potash, this hardens growth and makes it more able to withstand frosts.  
• Order 30 gms fleece well ahead, or at least have old sheets, netting, etc to hand. We find 3 – 4 layers of fleece will keep several degrees of frost out of our polytunnels providing there is an air gap between them.
• Have a covered frost-free area, hard prolonged frost will eventually get into garages etc, so insulate and possibly set up lighting. 
• Before spending a lot of money on large plants e.g. Tree Ferns and Palms do some research and get advice.  If you can’t or are not prepared to protect them then maybe think again.
• After a cold winter wait to see what may come back. Good news: some plants which look dead may still come back into growth albeit late, even mid-summer. Woody plants will often re-shoot from below ground.  Some plants on the other hand may appear to have survived but then keel over when the sap starts to rise and puts stress on them.

All this does require some planning to ensure your plants are protected well ahead of any cold weather, to avoid a last minute rush,