Growing in sand
Peter Korn at the Beth Chatto Symposium, quarries, Chatto Wood and creating an experimental raised sand bed
I have long been interested in sand and aggregates as a planting medium. In fact, this interest goes back to my research days when I was working in quarry restoration and growing climbing plants in sand and waste quarry materials.
Listening to Peter Korn’s talk at the recent Beth Chatto Symposium got me digging out my thesis to remind myself of what I was trialling in the 1980s. The aim was to use climbing plants to kick start colonisation in quarries, their trailing stems and fallen leaves would help create microhabitats, which could trap organic matter, moisture etc and enable other plants to colonise. I have included a few photos of my research site, an abandoned quarry in Shropshire and the sand that I was using as a planting medium to grow old man’s beard (Clematis vitalba), ivy (Hedera helix) and Russian vine (Fallopia baldschuanicum). It was surprising just how well they could cope with aggregates as a rooting medium.
I also found that some plants were immensely tolerant of quite wide ranging conditions. The clematis for example, is typically a calcicolous plant that is found growing on chalky sites. I grew it on a range of sands, from pH 4 to 8. The source material came from different locations and while most of the plants couldn’t cope with the acidic sand and soon became chlorotic, cuttings taken from one site in Surrey grew well on all sands, so were far more ‘plastic’ and adaptable, something which could enable them to survive and colonise perhaps. In fact, the current distribution of this species is far wider than 40 years ago.
Recently, I returned to the quarry and found it to be completely overgrown with a dense scrubby woodland, with ivy on some of the quarry faces.
Peter Korn
I was interested to learn about Peter’s experiments with growing in sand. In case you don’t know, Peter has pioneered the use of sand as a growing medium. He lives with his partner, Julia Andersson, near Malmo in Sweden where he has a garden and nursery. His aim with his first ‘garden’ was to grow the most challenging of plants in a Swedish climate, for example, he was growing sub tropical and alpine plants and this was achieved by recreating conditions similar to those of their native habitat. He then moved to a Klinta Trädgård in southern Sweden and changed his focus to growing plants in challenging locations and he has used this knowledge to create roof gardens, green walls, and coastal gardens etc. All tend to be low maintenance with high biodiversity.
Peter set up a nursery to raise plants for his design projects and they are all grown in sand beds around 20 cm deep. He believes that the plants he produces are tougher and better suited to low maintenance plantings in public spaces etc. He rarely waters, even in a drought. The top layer of sand may be dry, but underneath there is moisture which the roots can access. In addition, the sand is soon colonised by mycorrhizal fungi and they will access water and nutrients for their plant partners. The lack of nutrients prevents lush growth, which is a good thing, as slow growth creates more resilient plants with a longer life. The key is to keep the organic matter content low, so the plants are cut back in winter and all leaves etc are removed. Another advantage of growing nursery plants in sand is that it is very easy to pull them from the ground and they suffer little transplant shock.
Peter has also experimented with mixing biochar into the sand. Biochar is a wonderful amendment. A product of pyrolysis (low oxygen), it’s a material that acts like a sponge, holding water and nutrients and creating microhabitats for soil life, so perfect for mixing into sand.
Chatto Wood
During the conference, we were told about the new housing development along the northern boundary of the garden. The developer had asked if they could call the estate Chatto Wood, and in return, the garden team asked if they could design climate-resilient plantings for the front gardens and public spaces of the estate, which was agreed. The Beth Chatto team designed low maintenance, waterwise gardens planted on a sand and gravel mix. Education was key to getting the new residents on side and they were warned that the plants would take several years to establish. Apparently, some of the more doubting residents were won over after a visit by Monty Don and the Gardener’s World crew.
Unlike a typical housing development, there was no top soil. Instead, there was 30 cm of a sand/gravel mix to create a beach look. The plants were mostly shrubs and perennials, with the team selecting smaller plants (9cm pots) which would establish more quickly than larger plants. All were well watered at establishment, and there was some hand watering during the 2022 drought where necessary. But that was all and its proving to be a climate resilient planting.
Maintenance is minimal. In spring, the shrubs are hard pruned and the perennials cut to the ground and all the prunings removed so there is no build up of organic matter. There is hardly any weeding due to the dry surface and the lack of weed seeds. Its only been a few years, but a biodiversity survey has found that the sand gardens have attracted 20x more insects compared with the lawned front gardens on the other side of the estate.
I wondered around the estate and was really impressed. The planting was looking good, full of colour, interest and importantly, insects. And it looked so more attractive than the standard front gardens with their tidy lawns.
Experimenting with sand
If this has intrigued you, why not create a sand bed? The easiest way to experiment with sand is to create a raised bed and fill it with sand to a depth of around 20cm or more. Peter recommends a sharp sand, that’s 0.05-0.08 mm diameter and, ideally, it’s prewashed to remove any lime or salt. If you are not sure if its shapr enough, do a cake test. If you can ‘make a cake’ of the sand, then it has too much clay present and it will dry out in summer.
When planting into this medium, give the plants tough love. First, wash off all the soil, and when in place, really drown them with water, so all the air pockets are filled with water. Remember that the plants won’t do much for the first year, and then in year two, they will start to put on more growth and get away. It’s slow progress, but the plants will live for many years without the need to feed.
The raised bed will be pretty low maintenance and waterwise. The surface dries quickly, so seeds don’t germinate, and if they do, the resulting plants are easy to remove. And remember to remove all the organic matter. Unlike a typical soil-based bed, you don’t want to build up organic matter.
What to grow in sand?
There’s a wide choice, including grasses such as Stipa and Sesleria, and perennials Achillea, Alchemilla, Aster, Calamintha (Nepeta), Echinacea, Erigeron, Eryngium, Gaura, Lychnis, Salvia, Verbena and more.
I think the easiest way is to experiment with one sand bed and just give it a go. But to be honest, having gardened on acidic sand in Hampshire for many years, it’s not that much of a step into the unknown!
If you have experimented with sand, or have some suggestions regarding plants to use, I’d love some feedback in the comments!!
Well done Yeovil in Bloom
And to finish, a couple of photos of a seasonal planting that I photographed the other day. It’s in Yeovil, which is not the most attractive of towns, but I love the planting in St John’s Churchyard, which is part of the Yeovil in Bloom displays. It has a lovely tropical feel and the plants have really thrived this year. I was quite envious of the growth on the Calocasias, so much better than mine!
Well done to the volunteers who have worked so hard to get it looking wonderful. After winning a gold last year, they were national finalists in the competition this year. Fingers crossed for a good result later this month.
Happy Gardening
Sally
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Talks
I am talking at a number of venues in the coming weeks. Most of these clubs allow non members to attend for a fee.
14 October Nynehead Gardening Club near Wellington
17 October Dulverton Gardening Club
19 November Mayfield Horticultural Society by zoom
21 November University of Bristol Botanic Gardens
23 November I am talking at the inaugural LandAlive conference at the Bath and West showground on Sat 23 November. The topic is on creating a climate resilient allotment.
4 December Castle Cary Gardening Club
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The Chatto Wood development certainly looks a much better option than many of the 'low maintenance' plantings I see around the housing developments up here. I've heard others talk about growing in sand but never tried it. So thanks for the further information - and perhaps an experiment for one of my containers next year.
I recently saw a talk by John Little of the grass roof company who was also advocating sand as a fantastic medium to grow in but also provides habitat for lots of types of ground nesting bees amongst other insects.