A Northumberland Alpine Gardener's Diary
This entry: 02 September 2012 by John Richards
A New Sand Bed (Entry 223)
Making a sand bed.
Once I have overcome the annual barriers of the hedge cutting, and bulb repot (the latter not so arduous as it once was), my mind has often turned to major garden projects as the autumn looms. I am scarcely a dedicated follower of garden fashion, but when I hear of a new growing trend, I am often tempted. So it was that I assayed a crevice bed some six or so years ago, taking in part of my raised terrace to construct it.
This crevice bed has been an unmitigated disaster almost from day one. Basically there have been two problems. One, it was rapidly overrun by uneradicable weeds. And, two, alpines didn't grow in it! There were three main miscreants among the weeds. Foremost was Cymbalaria hepaticifolia, an ivy-leaved toadflax relative which is one of the worst small scale weeds I have encountered. Underground this forms a mass of 'spaghetti' and was rapidly joined by THE worst weed in this garden, vetch, Vicia sepia, another brand of sinuous pasta. Add the self-seeding ramifications of violet, Viola riviniana, and very soon there was little room for alpines. One of the problems with this sort of attack is that one cannot use chemical control, for fear of damaging the alpines with which the weeds have become inextricably intertwined.
Undoubtedly the weeds contributed to the failure of the alpines, but it had not helped that for soil I had used old potting soil which in those days I used to dump for a year and then re-use. Although of good structure and well-drained, this seemed to be devoid of nutrient and plants did not grow in it. For rock I used a local vein of shale, set vertically, which the plants also seem not to enjoy.
By this summer the bed had become such a mess that I resolved to dig it all up and start again.
To start with I removed all the surface rock (shale) that had been used to provide vertical crevices, and stacked it, making quite sure that it was completely clear of clinging cymbaralaria. I then removed the alpines. This was a lengthy job as many had been infiltrated with cymbalaria, vicia and viola, so that many of the cushions had to be divided many times to make certain that they were free of weed roots. Luckily the 'spaghetti' is very visible. It is important that every alpine is inverted and the root system thoroughly investigated from below.
Plants were stored in folded 'dumpy bags' in a coolplace, out of what little sun we have recently received.
Then the 'soil' (mostly grit) was removed to a depth at which the occurrence of weed roots ceased (about 25 cm) and dumped next to the hedge in a far corner of the garden where such things lie forgotten! Here is the bed stripped and ready for the next move.
Next, I barrowed in four loads of compost. This well-rotted compost is free of perennial weeds. When used as a top-dressing, it proves to be full of annual weed seeds, but here it was due to be buried deep, so that weed seeds should not be able to germinate.
The plan was to replace one fashionable disaster with another fashion icon, the sand bed, hopefully less disasterous than its predessor. This might seem a curious move, bearing in mind that one of the faults of the previous incarnation seemed to be lack of nutrient. Nothing, you might think, is less nutritious than concreting (coarse) sand. However, I have seen several examples recently in which alpines seemed to be flourishing in pure sand, and indeed I built just such a raised bed myself at the University of Newcastle Botanic Garden, Moorbank, this spring. In this wet summer, results there have been greatly encouraging.
So I ordered two tonnes of concreting sand from our local builders merchant, which the skilful driver as ever parked by the front gate in such a way that the car can still pass safely, a miracle indeed!
Then it was just a matter of shovel and barrow, uphill and most of the length of the garden. Much better than aerobics at the gym! Consequently I am a bit fitter, a couple of kilos lighter, and my back seems to have survived.
Here is part of the load dumped on top of the compost which eventually lies under about 30 cm depth of pure sand.
Here is the first tonne of sand evenly distributed.
When about half the second tonne had been barrowed in the sand was judged deep enough and the bed was replanted, with some of the alpines that had been there before, a few plants in pots surplus to the needs of exhibiting, and many of this years seedlings and cuttings. After that it rained a lot (what a surprise!), obviating any need for watering.
The final step (so far) was to use the surplus shale as top dressing, horizontally rather than vertically this time, making sure that stone sloped inwards, and was bedded strictly horizontally.
The area has still to be top-dressed with some sandstone gravel, but to this point it looks okay. I am quite pleased with it.
Those of you that have been counting will have realised that (actually rather more than) half a tonne of sand remained. This has enabled me to finish filling one of the bulb plunges in the alpine house (started this time last year) and to more than half fill the second. Here is that plunge with 50 pots of dormant bulbs (the collection is slowly building up again after the nadir of the two hard winters 2009/10, 10/11) and a view through to the other alpine house.
Back in the garden, the best plant by far is our Eucryphia 'Nymansay' which has benefitted from the removal of a lime tree two years ago, and from several wet summers, to flower as never before. It is now over five metres high and a spectacular sight.
I am also delighted with a Lilium henryi, grown from seed. This was sown early in 2006, and is flowering for the first time, having been planted out in the spring of 2011. Already it is huge, about as high as a man, 1.7 m.
Lilium 'Cover Girl' is flowering as well as ever, although as it has not been tied up and the rain has been heavy, more horizontal than vertical in format!
Not many alpines in flower at this time of year, but here is Gentiana paradoxa in the garden, followed by a very red-spidered Campanula oreadum in the alpine house (query, why does C. oreadum not get red spider on Olimbos? its hot and dry enough there at this time of year!).