Saving Trengwainton’s special plants from disease

Florets dissected in the labratory of the micropropagation unit, Duchy College

When the Bolitho family donated Trengwainton Garden to the National Trust in 1961, it was the significance of the plant collection that made it so special. Now with the threat from a virulent disease, it’s science that’s coming to the rescue.

What makes the plant collection special

The core of the plant collection originated from seed brought back from the great plant hunter Frank Kingdon-Ward’s expedition to north-east Assam and upper Burma in 1927-28. Some of these plants flowered for the first time in the UK here at Trengwainton.

Head gardener Alfred Creek was responsible for establishing these plants and his successor G W Thomas was renowned for creating hybrids. Over the years the garden has been awarded numerous accolades from the Royal Horticultural Society for the quality of individual plants within the collection.

Why it’s now under threat

Phytophthora ramorum (and the Cornish strain Phytophthora kernovii) is an aggressive, fungus-like disease that’s causing serious damage to a wide range of ornamental plants. It was originally known as Sudden Oak Death because of its devastating effects on native oaks in the USA, but it now affects a whole range of species.

Several rhododendrons, magnolias, camellias and pieris at Trengwainton have died because of the disease and those that are left remain vulnerable to infection.

How we’re fighting back

We’ve teamed up with Duchy College Rosewarne who are using micropropagation techniques to save some of our key rhododendron strains.

The technique involves taking small pieces of plant material, sterilising them in diluted bleach then growing them on in a nutrient jelly with added plant growth hormones which allows manipulation of the way the plants grow.  

It’s costly and time consuming – it can take a minimum of two years to produce rooted plantlets – but many rhododendrons have been rescued from certain loss.

The Noah’s Ark of plants

When the plantlets are old enough, they go to the Plant conservation centre which the National Trust set up to maintain and enhance the internationally important plant collections in our parks and gardens. 

In this state-of-the-art centre, the plantlets are weaned off their nutrient jelly and into compost and at around five years of age they’re strong enough to be transferred to carefully chosen gardens.

An international endeavour

Those gardens won’t just be those under the care of the National Trust, but the Plant conservation centre partners with gardens all over the world to give the plants the best chance of thriving in a disease-free environment once they’re reintroduced to the great outdoors.

Looking to the future

In recent years the control and containment of Phytophthora ramorum has become the biggest challenge which we must  overcome, along with the ongoing changes to the climate.

It’s a challenge we must continue to address to ensure that future visitors to Trengwainton can experience the horticultural legacy of this special place.