Wisley's Alpine Diary
This entry: 09 June 2011 by Paul Cumbleton
Wisley’s Alpine Log
By Paul Cumbleton
2011: Log 90…09 June
I thought it was time I gave an update on the crevice garden. Zdenek taught us how important it is, to achieve the most natural look, that we insert small slivers of stone between the larger slabs when we are finishing off planted areas. We completed one small area like this in order to show our visitors what the entire crevice garden will look like once it has all been done this way:
Before we can do this, there is still a lot more planting to be done. We have been raising things from seed, acquired through all the various exchanges as well as buying some from various sources. We sowed about 440 packets of all kinds of alpines through last winter and this spring. Of these, about 260 have germinated while 180 show no sign. This gives a success rate of 60% in the first year. I wonder how that compares to other people’s experiences with seed? – I know some of you keep very good records of germination so it would be interesting to hear your results. Of course, I hope that many more will germinate next year after they have been through another winter.
Some of the seedlings we have been pricking out straight into the crevices, as soon as they are large enough to handle, while also potting some up to grow on in pots until they are larger before planting them out. Personally I have found (in my experience with the sand beds at Wisley) that they do better if planted out once they have grown to fill a 7cm square pot (the sort of size you might typically buy an alpine plant from a nursery). I know this goes against the wisdom that pricking straight out into crevices leads to better establishment, but I simply don’t find this to be the case. Anyway, we have done some and some so we will be able to gauge long term which does best.
The initial plantings were of plants we bought and many of these have been flowering already. This is the delightful, diminutive Verbascum acaule:
Some are only temporary, being annual or biennial such as this Androsace bulleyana:
Dianthus are of course a must and we have planted many such as these three:
Above: Dianthus 'Eleanor Parker'
Below: Dianthus 'Eileen Lever'
Dianthus 'Conwy Star'
Armeria is another popular genus we have used and as well as the usual pink shades we also put in the white form of Armeria juniperifolia:
Amongst the brooms, Cytisus ardoinoi from the maritime Alps is probably the smallest and most desirable. They resent root disturbance so we did not expect this one, rescued from the raised beds that previously occupied the site, to survive, but so far it seems happy:
There are quite a lot of plants from North America in the crevice garden. Here are just a couple of examples:
Phlox longifolia ssp. brevifolia:
Getting these plants established during what has been the driest spring ever recorded in the south of England has been a challenge. It has not been helped by the fact that there is something unusual about the sand we have used for the crevice garden. We regularly buy washed, sharp sand for use in filling plunge beds or sand beds or, as in this case, the crevice garden. Being a natural product, each time you buy a load it can vary somewhat in its make up – different colour, particle sizes etc. It can even vary quite a bit between different batches from the same quarry. But usually whatever we buy, we expect water to soak in and then drain away well. But this sand is different - it seems to be hydrophobic! Water simply doesn’t go into it – it sits on the surface and then just rolls off in beads. This has made watering a real problem. Does anyone know why sand might behave like this? I don’t think it has anything to do with the sand being coated with something greasy (I have tried using wetting agents to no effect). I guess it may be something to do with the shape of the grains and how they pack together. But I am no expert in this area. I know there is little we can do about this now, but it would at least be interesting to know why this is happening. Does anyone know about these things? Replies via the forum would be appreciated.
One last plant to finish. I have used quite a lot of plants with white flowers on the crevice garden as white seems to really stand out against the colour of the rock. This one is another common but very useful plant, Silene pusilla: