Semi-hardy plants to try from Cornwall!

Having driven down to Cornwall for a camping and garden visit holiday, I was amazed at how a few degrees of extra warmth from the Gulf Stream allows one to grow such an amazingly different range of plants.

Though I live in London (and its heat blanket) it still gets much colder here than Cornwall does. At the Lost Gardens of Heligan the lowest temperature they have recorded in 25 years -6, and that was only one night. Their average low is 0 degrees, even in the depths of winter.  London has regularly been down to -5 for the last for years, and outside London it’s been much colder.

Being a fan of semi-hardy plants, living in Cornwall would mean no wrapping tree ferns in fleece, freely growing Proteas and other South African semi-hardy plants outside, and having a much longer growing season. Very jealous…

But that said, it’s worth having a go with some of these unusual looking, and amazing plants even if you live in cold parts of the country, as the results can be spectacular.

If you’re looking for something different for your garden, and love to try pushing the limits with what you can grow, I would recommend the three plant types below.


I grow all 3 in London, and with a bit of care and luck you’ll get some good results too!


These stunning plants produce the most amazing flowers, and have beautiful foliage and are worth a go! Generally in the UK it’s advisable to bring them into a greenhouse or covered patio during the winter, but this does depend where you live. There are hundreds of types, so make sure you get detailed growing instructions when you buy.

Image 1:  Silver Tree at Minak Theatre (on the left, with Echium Pininana to the right)

Image 2) close up of silver tree – look at the amazing Bark and leaves

Image 3) Protea growing in someone’s garden – thanks unknown gardener!

Care and requirements:

  • Requires loamy soil, well drained, course sandy feel.
  • Wind tolerant, not so tolerant of salty conditions (though the Silver Tree, Leucadendron argenteum is a bit more tolerant of wind and salt. Minak Theatre has some stunning examples of the Silver Tree, considered to be one of the most beautiful Foliage trees in the world, growing right on the edge of the sea facing cliff).
  • Watering: depends on the species, but none like to live in very damp conditions, and do not like wet feet.
  • Generally considered to be not hardy, but some species can tolerate temps down to -4 (especially species from around Cape Town in South Africa)

Tree Ferns:

There are many types of tree fern, but the most common one in the UK is Dicksonia Antarctica.

Others considered OK to grow in the UK outdoors are Dicksonia Fibrosa, and Cyathea Australis.

As the name Dicksonia Antarctica suggests, this tree fern grows in colder conditions, and can tolerate temps of -10 for a short time. It is advisable to wrap the trunk and the crown in fleece, or to create a cage of chicken wire and stuff it with leaves. If the crown dies / dries out, the whole plant is dead!

The Lost Gardens of Heligan have huge specimens growing in their jungle valley that were abandoned for over 50 years, and are still growing fine, without any protection at all.

Image 1) the oldest tree ferns in the Lost Gardens of Heligan, considered to be over 200 years old

Image 2) the graceful beauty of the unfolding crosiers on a young tree fern

Image 3) though not a true tree fern as it does not form a substantial trunk, Blechnum Chilense grows to approx. 5 foot tall, is totally hardy in the UK,  and has much of the grace and delicacy of a true tree fern. It also spreads easily forming a fern grove rather quickly.

Care and requirements:

  • Requires humus-rich, neutral to slightly acid soil.
  • Not so wind tolerant as these are undergrowth plants, and not very salt tolerant.
  • Watering: must be kept damp at all times. This is critical. Tree ferns will die if the whole plant, especially the trunk is not kept damp. I water mine on a daily basis, watering the crown, trunk and soil. This said, they do not like to sit in water, so make sure you have well-drained soil.
  • Considered to be semi-hardy / hardy, depending on the type. I always wrap mine for the winter, and have not suffered a loss yet.


This amazing group of plants sends up the most spectacular flower spikes of almost any plant out there! Some types are perennial, but most are biennial. These plants in their first year are not particularly pretty or large, but in their second year they send up a 3-5 meter flower spike, covered in intense small blue flowers. This is an amazing show plant, and stops everyone in their tracks when in flower. Most people grow Echium Pininana though recently perennial varieties from the Canary Islands have been on sale at many garden centers.

The best examples I Found were at the Minak Theater, however, they were also growing all around St. Ives, and in people’s gardens. They appear to self seed without problem there, but in the rest of the UK you will need to grow from seed on a yearly basis.

Image 1 / 2)  Echium Pininana at Minack Theatre. The silver tree in image 2 is over 4 meters tall, and the Echium Pininana towers over it.

Care and requirements:

  • Tolerant of many soil types, and can self seed almost anywhere. The better the soil, the better the flower spike.
  • Wind tolerant (bearing in mind it can grow to 5 meters tall, so heavy winds can uproot it) and salt tolerant.
  • Watering: can tolerate dry conditions, but prefers a constant water source, without water-logging
  • Considered to be Semi-hardy, can tolerate conditions down to -4 for a couple of nights. If you live in a cold area, plant in a heavy pot, and bring into a greenhouse / covered patio for the winter

Written By Colin Copeland

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