Crathes Garden blog #2: a global perspective

Crathes Castle Garden is famed for the diversity of its planting; for centuries plants have arrived from across the globe. Sir James Burnett (1880–1953) and his wife Sybil Crozier-Smith (1889–1960) were the principal architects of the diversity, and the National Trust for Scotland has since tried to honour their vision. Whilst we celebrate the diversity, we have learnt, to our cost, that some plants can be invasive. The most destructive at Crathes, and across much of Scotland, is the Rhododendron ponticum that was introduced in the 19th century for game cover and for its decorative flowers. Since the late 20th century, the ranger service and volunteers have been trying to eradicate it at Crathes, but during the last 18 months it has had free rein. Just recently, the local scouts have renewed the attack. I have written about rhododendron eradication elsewhere. [1]

Other nuisance plants that James Hannaford, the head gardener, is keeping an eye on include skunk cabbage (Lysichiton americanus) and white butterbur (Petasites albus), both of which grow in the Woodland Garden. Gunnera can also be invasive. At Crathes we do not have, I think, the invasive Gunnera tinctoria, but instead we have G. manicata, which is not a problem. The large leaves of these species are a problem if they begin to spread. There is some skunk cabbage on the Coy Burn, which is under the eye of the ranger service, but it is likely to have come from upstream since there are no water courses in the Woodland Garden – just a boggy area where the skunk cabbage and gunnera grow – so the threat of spreading from here is much reduced.

The Gaultheria shallon that grows in Caroline’s Garden is currently being dealt with by the rangers, along with essential help from Branching Out volunteers. Branching Out is an NHS partnership organisation that helps people connect with nature and enjoy outside activities. Gaultheria is a North American plant that has become a real nuisance in certain areas of lowland forest and heath; like the rhododendron, it was planted for game cover. Its deep roots mean that, once it is established, it is difficult to eradicate. Cutting back is not enough to remove it, but a treatment with herbicide following cutback should do the trick. Herbicide is used reluctantly but is sometimes appropriate on target species. If this potential threat is removed now, it could save heartache in the future.

Reducing the diversity in the garden is not the answer to invasive plants. Our gardens would be so much poorer if we only grew native plants. The Royal Botanic Garden Edinburgh (RBGE) plays an important role in global conservation, holding living collections of plants, such as the endangered monkey puzzle tree (Araucaria araucana) and Patagonian cypress (Fitzroya cupressoides), both from Chile and Argentina. Here at Crathes, as at many other estates in Scotland, we hold some specimens of international endangered plants as a safeguard from local dangers, such as wildfire or disease, that might hit the RBGE collections. The young arboretum at Crathes has a few such plants.

This year the Invasive Species Week was held from 24–30 May. By coincidence, I was in North Berwick on 29 May, taking a trip round the Bass Rock and Craigleith islands, just off the coast. The coincidence relates to SOS Puffin, a project involving the invasive tree mallow (Lavatera arborea), which has covered Craigleith. The mallow can grow over six feet tall and its roots prevent the puffins from making their burrows. The boat trip took place in thick fog and rough seas, but we did manage to see some puffins and lots of gannets.

Emily Burton, Conservation Projects Officer at the Scottish Seabird Centre (SSC), filled me in on the project. Around the turn of the century, puffin numbers on Craigleith had crashed from around 10,000 to less than 1,000. Tree mallow was dominating the island and also spreading to other islands in the firth, possibly as a result of global warming. For 14 years, 1,300 volunteers have helped to control this mallow, and puffin numbers are now increasing. There are estimated to be 4,100 active burrows this year – each burrow representing two adults. Tree mallow, which is considered native by some experts, is found on off-shore islands and coastal areas in Britain. [2] It is thought to have been introduced to the Bass Rock by soldiers in the 17th century, possibly for medicinal reasons. The University of Aberdeen has been involved in SOS Puffin, testing soil samples for seedbed results, since seeding is the main way of mallow spread. So far, it has not been a problem on the mainland coastline.

It was a week of coincidences. Two days later, I was photographing the lovely wildlife garden outside the SSC office. Noting my interest, someone – I later learnt she was Susan Davies, Chief Executive of SSC – came out to talk, and it turned out that early in her career she had volunteered at Crathes and Drum castles, staying in a wee cottage on the Drum estate. At Crathes she had helped with education and footpath maintenance, but at Drum her work was with another invasive plant: bracken (Pteridium aquilinum). Bracken is a native fern but can be invasive. At Drum, the Old Wood was suffering from excessive undergrowth, preventing regeneration of the oak trees. Susan’s job was to help look after the pigs that were used to root up and eat the bracken. Roddy Hamilton, from the North East Ranger Service, tells me that bracken is still a problem; he is going to be bracken bashing at Drum shortly. Sometimes they take in horses for a day to trample and drag a raft over the undergrowth – although they have to avoid damaging the young oaks. The Branching Out group, mentioned earlier, has been helping to mark the young oaks.

Susan also told me that there is still some mallow on the Bass Rock in inaccessible places. Although herbicide has not been used so far in the project, it is felt that it is appropriate to use it in such places to prevent further spread by seed. In the same week, the World Wildlife Fund announced that puffins are high on the list of globally threatened species, which makes the work on Craigleith of international importance. Unfortunately, the puffins are also threatened by shortage of food, as the sand eels that they feed on are in turn threatened by global warming.

At Crathes, James is always aware of the implications of action in the garden regarding the climate crisis. The dipping pool that was uncovered in December, and originally used for watering the garden, is exciting not only because it will make an attractive feature, but also because of possibilities for water conservation. Even through the dry weeks of April, the water that drained from the garden kept flowing along the main drainage pipe. After the water leaves the pool and goes under the road, it connects to an old well. It may be that a pump could return this water to a holding tank that could be used around the estate and garden, and in the glasshouses. Since water is presently metered, this would save a lot of money as well as water. Meantime, a local contractor has dealt with the crumbling concrete in the pool; there now just needs to be an adjustment to the various pipes that connect to the drainage so that the pool can fill up and planting can begin.

Water conservation is one of the aspects that Tim, our apprentice, has been considering in his report about the carbon footprint of the garden, which is now almost finished. He says that writing the report has made him much more careful about conserving water in his own life; he never now, for example, spends long in the shower.

In the glasshouses, there is also a return to past habits. Joanna is slowly replacing the plastic pots with clay, especially in the show houses. The pelargoniums look great in the terracotta pots. They are all grown from cuttings taken last year. I never realised how many different kinds there are, both in the wild and in the cultivars. The show houses are now open to visitors.

We are still counting the cost of the late hard frosts, with some shrubs looking dead and others slow to catch up despite the lovely warm weather – we went from winter to summer in the last few days of May. The handkerchief tree (Davidia involucrata) looked to be barely alive on 25 May but by 11 June it was looking fine, although many of the white bracts had blown off and were lying on the ground. The tender Fremontodendron californicum was thriving and I was surprised to see that a row of night scented phlox (Zaluzianskya ovata) had survived the winter and is in full flower.

I am also pleased to see that there is evidence of more mining bees in the Fountain Garden. Although I didn’t actually see any bees, they leave a pile of grey dust where they have pushed up through the red surface of the path. What I did see was an oystercatcher. I nearly missed it sitting in the middle of the agapanthus pot. Oystercatchers often try to breed in the garden, usually without success. I had noticed the scrape earlier and wondered; Cecilia tells me there are three eggs. The camouflage afforded by the growing agapanthus will maybe protect the eggs from crows, but how will the chicks fare when they hatch? If they fall off the pot without harm and move quickly into some vegetation, they may well survive. Fingers crossed.

The problem with weeds continues. When I visited on 7 June, the first thing that met me was a barrow full of weeds, particularly the dreaded thale cress. Some planting had started, but with the ground so dry it will be expedient to plant out when the forecast is for rain. The gardeners were weeding in the Red Garden where the central bed had been already been planted with Nicotiana ‘Cuba Bright Red’ and Amaranthus caudatus. The Viburnum plicata ‘Dart’s Red Robin’ has a lovely shape and was in full flower; in the autumn it will be covered with red berries. By 11 June the Red Garden is weeded and fully planted, with dahlias and aeoniums newly added. There has been no rain of any note and the gardeners are forced to water because the planting cannot be delayed any longer.

As predicted, the June Border is a little slow but coming along nicely. A good spell of rain, preferably in the night, would help.

Here are a few other plants that give Crathes its reputation for diversity:

• The golden rain tree (Koelreuteria paniculata), planted a few years ago on the Aviary Terrace, has survived the hard frosts well. Sometimes called the ‘Pride of India’, it is native to China. Sir James Burnett planted this tree in the Yew Borders in the 1930s/40s and it survived until at least 1979; its replacement hasn’t yet flowered. In the USA, it is listed as invasive.
• Rhododendron haematodes was discovered in Yunnan by Abbe Delavay, and later collected (as seed) by George Forrest.
• The Trillium rugelii mentioned last time is now showing its white, strongly recurved petals and dark stamens. It is native to the southern Appalachians.
• The lady slipper orchid (Cypripedium ‘Ulla Silkens’) is a cross between the red American C. reginae and a yellow Russian/Himalayan C. flavum.
• Also from the Himalayas is the blue poppy (Meconopsis). The pink Meconopsis x cookei is a hybrid raised from M. punicea and M. quintuplinerva.