Wikipedia describes it as: " a biological environment based on a limestone plain with thin or no soil and, as a result, sparse grassland vegetation. Often flooded in the spring, and affected by drought in midsummer."
Here is what part of the alvar looks like at Roche fleurie. As you can see on the right, a stone pavement, just about as smooth as a concrete floor, which is crisscrossed by crevasses such as the one on the left.
Very specific plants grow in these crevasses.
The crevasses form regular rectangles covered with moss and lichens, when, as in this case, they are in the shade.
Inside the crevasses, the most common plant is the little maidenhair spleenwort, Asplenium trichomanes (bottom left in the picture), but you sometimes also find the Christmas fern, Polystichum acrostichoides, on the right. Both of these grow in moss and send out roots in the limestone. There is no soil.
When the limestone is in the sun, it gets covered with Sedum acre, the plant pictured in the masthead of this blog, which gives its name to the garden.
|Close-up of plants growing in a crevasse|
You might wonder how trees manage to grow there. They can only survive if they get their roots in one of the crevasses. When there is shallow soil over the alvar, you can guess where crevasses are because that is where the trees are!
I expect there are small caves in some of the crevasses because, when they are wide enough, they seem to be popular home sites for porcupines. Wedged in a cave below ground, no one can get at them, and it is warmer in winter. Snakes are also supposed to overwinter in these crevasses.
Below is how the place looks where soil has accumulated over the limestone plain. Trees are growing where soil is deep enough. There is no tree in the foreground because the soil is just about 6 inches deep. The small trees beyond the foreground on the left probably have their roots in an covered crevasse. They might survive for a couple of years, but when we next get a dry summer (as we regularly do), they will dry up, if they have not been able to sent roots deep down.
The garden was made in an area just like the one above. In places, the soil is only about one foot deep. The deepest soil in the garden is four feet deep (much of it sub-soil). It was quite a shock when I realized how little soil there was. Our previous garden was in an ancient river bottom where in some areas the top soil was five feet deep.
|Area where the bedrock is very close to the surface|
Raised beds are a must, if only to ensure there is enough soil under the plants. Raised beds provide good drainage and since the water table can be quite high, most plants can sink some roots to the water below. This means that little watering is required. In fact, all watering is done by hand.
When the beds were created, top soil was removed where paths were to go and was replaced with limestone. This extra topsoil was put on top of the beds. You can see how close to the surface the bedrock is.
|Construction and resulting raised beds|
It turns out an alvar can be a great place for a garden!
How often our ignorance makes our lives better!ReplyDelete
You are quite right. Had we known how little soil there was we might not have bought the property.Delete
What you have achieved is quite incredible Alain.ReplyDelete
Really fascinating! I can see how you would have to do almost everything in raised beds.ReplyDelete
Your garden looks absolutely fascinating!ReplyDelete
This is similar to areas in the Yorkshire dales such as Malham where there are large areas of limestone pavement. The flat bits are called clints and the crevices are grykes. As in your area the grykes have their own micro habitat with plants making the most of the shelter. In the same type of area are networks of large caves, Is the same true of your area?ReplyDelete
I looked at pictures of Malham and it is similar. Yes, there are caves. SeeDelete
How interesting. I think there's pros and cons to gardening in most conditions but this is something else.ReplyDelete
The are a fait bit on "cons"!Delete
So fascinating, never heard of an alvar before. Gardening in these conditions may not be too difficult but I suppose you have to take into account that you cannot grow everything, as you already told trees often don´t survive.ReplyDelete
You are right. The limestone makes it very alkaline so acid loving plants are mostly out, so are plants that relish deep moist soil - things like ligularia or thalictrum.Delete
So interesting. I had not idea what an alvar was before now. I would love to see your garden someday.ReplyDelete
If you ever come this way let me know and we will arrange a visit.
I take my hat off to you Alain - what an incredible place to garden and learning about the different plants that will thrive must be quite interesting.ReplyDelete
I have to admit that your title gave me no clue as to what your post would be about - I had not heard the term alvar before.
I did not know either what an alvar was. I am still surprised by the number of plants that can put up with it.Delete
Thanks for explaining your unique garden conditions! The rock makes for beautiful character between the raised beds. It's incredible how some plants can thrive in those conditions!ReplyDelete
It's amazing you can garden there at all! The plants must be so rugged. I didn't realize ferns could grow in rocks. all the more reason to be so proud of what you've created. But your river bottom sounded like heaven with all that top soil.ReplyDelete
I was in our old garden (5 feet of top soil) for 25 years and never realized it was exceptional. You planted something and it would grow beautifully. I presumed all gardens were like that. It was a shock when I started gardening here and realized that just digging a hole was not enough!Delete
Very interesting post, Alain! BTW most of the Northern and Western part of Estonia is sitting on limestone bank, and we have quite a lot of alvars too. We use the very same term for them, though there is a Estonian word as well - "loopealne" :-)ReplyDelete
Alvars in Estonia have a thin soil cover, less than 20 cm and are considered one of the richest biotypes.
They seem more common than I would have thought. Much of the alvars here also have a thin cover of soil. It creates a kind of meadow as trees cannot settle there. They sprout but eventually die because it gets too dry in summer.ReplyDelete
Hello Alain : )ReplyDelete
I had no idea of the circumstances that you garden in.
It is amazing in fact .. I would have been totally discouraged .. yet you got on with it and created the raised beds.
You asked about photo management .. I fly by the seat of my pants with that.
Of course they are first filed by date .. then sub folders of edited pictures (sized for the blog) .. then a general one of the year with the best pictures .. I should do separate files for "same" plants .. it can be overwhelming though so a little at a time during the down season !
Joy : )
Alain, I did not know about alvar and now I think that it's a great work to grow anything in that place! You did raised beds, put the stones on their bottom, etc.ReplyDelete
I have my garden on the ancient bog and there is 3 m of turf in a soil. I have raised beds too and suppose it's good for my plants.
I can now understand the background to some of the wise and philosophical comments you make on my blog.ReplyDelete
I know you regard every challenge as an opportunity.
What a special growing environment you have!
A fascinating post. I had never heard of alvar. What a challenge to create a garden with little or no soil. But you grow an enormous range of plants. And your wild flowers are so exotic.ReplyDelete
Hello Alain, I must admit that they don't look like much from far away, but get up close and with the help of a magnifying glass (and kneeling pads), entire miniature worlds are revealed!ReplyDelete