Wisley's Alpine Log

Sand Beds part 2

Last time I started describing the two sand beds we built and showing dome of the plants that have done well. This week I?m going to continue the same theme. This is the other of the two beds, as it was in May of last year:

Ideally, sand beds should not have a grit topping as the whole idea is for the sand to dry out quickly after rain whereas the grit acts as a mulch and keeps moisture in. However, on this bed children could not resist from digging in it, perhaps used to sand being something they usually only encounter on a beach, so we put just a thin covering of grit to disguise the fact that it is sand. For some reason, perhaps because the stones are much closer together, they do not dig in the second bed so we left that with no grit topping.  This has largely solved the problem ? except that our cat Sunny is cleverer than children and is not fooled by the grit. She continues to dig in this bed from time to time!

Last time I mentioned that we put a few annuals or biennials in each year to add some extra colour. Another of these that does well is Androsace bulleyana. I put a few in as a test last year and was pleased with how well they did. I aim to plant a bigger number of these in future.

Back to perennials now and Leuzea conifera has settled in well and seeds it self back into the bed here and there:

I have always liked this Centaurea relative since I first saw it on a nurseryman?s stand at an AGS show many years ago. From dry sites in various parts of southern Europe, it tends to resent winter wet and doesn?t usually survive if unprotected from rain outside over winter. But given the protection of a roof for the winter it does well in the sand beds. Our landscaper, Peter Herman built our roofs for us, using a framework of timber to hold panels of twin wall polycarbonate. The support posts fit into metal fence post holders which are concealed under the sand. We put the roofs on about the beginning of October and remove them again towards the end of February.

Back to the plants now. Coming from sandy sites, it is not surprising that Mertensia maritima has taken to life in the sandbed. This plant often will not grow well confined to a pot, but can prosper if planted out with a free root run in sandy conditions.

With typical malvaceous flowers, Tarasa humilis has proved to be less easy in cultivation than many thought it would be. This is a pity as this plant, which in the wild comes from Chile and Argentina, is a dwarf and showy representative of a genus that otherwise has few noteworthy members. I had hoped that it may take to life in the sand beds, but although it survives and occasionally produces the odd flower, it doesn?t thrive and adopts the appearance of a plant promising to suffer a slow, lingering demise.

A plant which I am really pleased has done well in the beds is Weldenia candida. I planted three of these in one of the beds and all have survived and thrived.

The intense, pure white of the flowers always attract comment from visitors. Though each flower lasts only a day or so, it produces a succession over a long period throughout May and into June. I suspect that these plants would not have survived the last cold winter if they had not been quite dry and with a little protection under the sand bed roofs. One or two plants kept in pots died last winter. If we have further severe temperatures I will in future move the survivors to a house with frost protection in winter.

I planted a couple of young Leptospermum in one of the beds, more in hope than expectation. They flowered well in their first year but I suspect the conditions will simply not be moist enough for them in the long run. But it is always good to experiment as plants can often surprise you.

Above: Leptospermum scoparium nanum ?Kiwi?

When first planting the beds I thought it might be best to plant small cuttings or very young plants or even sow seed direct. However, experience has shown that they establish much better if grown first to the size where they fill a 7cm diameter pot and are then planted out. The low nutrient levels in the beds are probably the cause of this. I don?t want to put more fertiliser in as I want to grow things ?hard? in these beds, so better to grow them to a reasonable size first. (It is noticeable that although several things seed themselves back into the beds, the seedlings grow extremely slowly and never make big plants). Once planted, water plants well in their first year until established, but thereafter watering can be pretty much left to the weather, especially if your beds are deep like ours.

Sedum oreganum thrives in one of the beds. As its name suggests, this comes from Oregon in the USA, but also occurs north from here to Alaska. This particular specimen was grown from seed from a collection by Ron Ratko of Northwest Native Seeds:

Giving a little height at the apex of one of the beds is a Nierembergia. I am confused about the species name of this plant. It is often seen labelled N. caerulea. The AGS Encyclopaedia has it as N. hippomanica while our botanists here at Wisley say we should be calling it N. linariifolia. Whatever you call it, it is such a good value for money plant as it flowers almost non-stop, indeed virtually flowering itself to death. Gladly it is easily replaced from cuttings that root easily at almost any time of year.

Some of the most successful plants in the beds have been the North American eriogonums which revel in the dry conditions. Just a couple that stand out are Eriogonum umbellatum, noteworthy for it brilliant yellow flowers, and E. kennedyi var. kennedyi for its wonderful silvery foliage:

To finish this week, a couple more plants that do well in the conditions are firstly Erigeron caespitosus and then Morisia monanthos: