The new Rain Gardens at Knoll

As part of our new Dry Meadow project (above), that we started last year we created a series of rain gardens. This was partly practical as we wished to control surface water run off that can become something of an issue during periods of wet weather, even on our generally dry sandy soil, and partly as I wished to grow and experiment with a range of plants (mostly grasses!), that would tolerate and even enjoy the varied conditions to be found in these features.

At a basic level rain gardens are simply depressions or even holes in the ground that allow for the collection and short term retention of excess water; and as such have been around in the landscape long before gardens were invented! It is just that as gardeners we have possibly rather overlooked this simple but hugely effective technique that can bring so much to our gardens. Over recent years as our knowledge and understanding increases there has been a resurgence of interest in these as garden features in their own right. Coinciding perhaps with our weather patterns increasingly offering very dry and then very wet periods which can cause major issues for both our gardens as well as the designed landscape. As we come to appreciate just how much plants can help us with rather more than just looking good, more and more urban and built environments are incorporating these features to our own benefit as well as that of the wider environment. Even in relatively small areas such as domestic gardens rain gardens can not only be a practical option they can be a very ornamental one as well.

It follows that soil conditions can vary, often pretty quickly, between very wet to very dry and so careful selection of plants that are able to cope with these conditions is key to a successful rain garden. Calamagrostis, carex, luzula, acorus, molinia and deschampsia all have the necessary adaptability to not only survive but to prosper in these radically changing conditions. Take for example Carex divulsa, a UK native sedge, that is not only beautiful but useful too. In the two images above firstly it is being used in a large scale urban rain garden as part of a tolerant palette of plants and secondly as a ‘meadow’ sedge in the dry and testing conditions of Southern California. While in the image below young plants are quickly settling in to our new rain garden (along with a few volunteer foxgloves). Adaptability is a good thing!

Another advantage of a sometimes damp environment is that there is usually some moisture around at least on occasion which has allowed the young plants, many of which have only been in the ground for a short while, to put on some impressive growth (two images below) in spite of the generally hot and dry summer.

We have four linked individual rain gardens so that as the water fills up in one it will exit via a pipe into the next slightly lower rain garden and so on. The top rain garden (above), will take the run off from our new learning centre once built, while the third is linked to the closeby Stream garden which is the source of much winter run off. The idea is for the collected water to percolate away into the ground and so avoid spilling over into other drier areas of the garden.

As you can see from the image below in spite of the inches of rain that have fallen in a short time frame just recently the system appears to be working; and this is before the plants have had a chance to establish and so help soak up the excess water through their root systems.

Plants used on the floor of this rain garden (above), include Juncus Carmans Gray, Luzula sylvatica Bromel and Deschampsia Goldtau, while Molinia Overdam is being used in association with the deschampsia on the slightly drier sides and moving up into the Dry meadow mix.

Looking across the top rain garden (below), with the second just visible across the bark pathway Carex divulsa is being used in the centre and floor with Deschampsia Mill End planted on the left side. Calamagrostis varia has already made large mounds of foliage to the bottom right of the image and has been interplanted with a few Filipendula rubra Venusta.

The second rain garden (below) is composed of Carex Everlime and Luzula Snowflake. The luzula seems to cope with a mix of wet and dry conditions and while most carex are also pretty tough I have not used Carex Everlime in a situation like this before. It is looking promising so far but it is a genuine experiment to see what might happen. Watch this space as the saying goes! Molinia Overdam is being used on the side and up into the Dry meadow mix again.

In the fourth and final rain garden (below), Acorus calamus, Luzula sylvatica Marginata and Luzula Solar Flair have all been used on the floor, while Acorus Ogon is planted a little further up along with some Deschampsia Goldtau. Molinia Dauerstrahl has been used around the mouth of the pipe as well as in places along the sides. This is pretty soggy at the moment!

It is of course very early days in the life of this project and the winter will no doubt be more of a true test for the planting, but I am really enjoying watching the plants grow and work together in what I hope will become a viable rain garden community.