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Tuesday, 25 February 2014

We’re gardenin’ in the rain

By Helen Roberts


It has been unbelievably wet since the start of 2014 with England experiencing it’s wettest January since records began over 100 years ago. The Somerset levels have suffered dreadfully and huge areas are still underwater and are likely to remain so for weeks or even months to come. From where I live, on the Mendips, I have far-reaching views over to Glastonbury Tor and the Quantocks and the area of levels in between looks like the vast inland sea it once was. In most other areas, the ground is completely saturated and in some places water is bubbling up to the surface.

Flooding in Greylake, Somerset in February, 2014. Photo
courtesy of Live-vibe on Flickr CC

What does waterlogging do to our gardens and what can we do to solve it?


Many plants do not like to be waterlogged because their roots need oxygen as well as water and nutrients. When roots are starved of oxygen they die and these dead roots can then act as a host for fungi such as Phytophthora, a root rot. Shrubs and fruit trees are particularly vulnerable to waterlogging as they cannot put on new roots as quickly as perennials and cannot stand long periods under water. Add freezing conditions with waterlogging and your plants may be in big trouble.

Winter flooding may not be fatal though, as many plants can experience and survive winter flooding for short periods of time. You can give your plants a helping hand if they’re waterlogged by pruning ornamentals right back so that they don’t have to protect so much above ground. You can also remove any dead or dying shoots and take cuttings as a back-up should the plant die. Smaller plants can be transplanted into pots with fresh compost, removing dead roots before transplanting.

Looking after waterlogged lawns is a different matter. If your lawn is squelchy to walk on at the moment, try to stay off it. Walking on it will only aid compaction and make matters worse. Waterlogged lawns can quickly lead to the grass dying and moss, algae, lichens and liverworts taking over. I do not have an issue with these plants in a lawn per se and I am not one to fret over weeds in a lawn either, but if you do want to make things better and improve a waterlogged lawn there are a number of options.

You can try pricking, spiking or slitting the surface of the lawn with powered tools or even a fork. This leaves holes that can be infilled with lawn top dressings or horticultural sand. It is best to get rid of surface water first, if possible, by sweeping it off with a brush into the borders. Otherwise, wait for it to drain naturally. Alternatively, convert your lawn into a water meadow!

Create a partnership with nature


Sometimes struggling against waterlogging in your garden or parts of your garden is a losing battle. It is simply better to accept the natural conditions of your garden and work with what you have. Rethink your palette of plants and cultivate those that favour wet soil. If the ground is permanently wet, consider establishing a bog garden as bog plants can be truly architectural in their habit and are excellent for attracting wildlife.

Some suitable bog species suggested by the RHS website include:
Herbaceous perennials: Bog primulas, Eupatorium maculatum Atropurpureum Group, Darmera peltata, Iris ensata ‘Rose Queen’, Iris laevigata, Ligularia ‘The Rocket’, Lobelia cardinalis, Rodgersia pinnata ‘Superba’, Trollius x cultorum ‘Superbus’
Grasses: Spartina pectinata ‘Aureomarginata’, Carex elata ‘Aurea’
Ferns: Athyrium filix-femina, Matteuccia struthiopteris

A sustainable approach to managing flooding

How we manage water and excessive water in our own gardens, particularly in urban areas where there is nowhere to drain excess water, is very relevant at present considering the amount of rainfall we have had over the last couple of months.
Sustainable urban drainage systems or SuDS are approaches of managing surface waters taking into account quantity (flooding), quality (pollution) and amenity issues of water. They ultimately contribute to sustainable development and improve urban design. These systems mimic nature and manage rainfall as close as possible to where it falls aiming to slow water down before it enters watercourses. This is basically done by forming structures and landforms that can store water and allow water to soak into the ground, evaporated from surface water or lost through evapotranspiration. 

The use of SuDS is not by any means a new concept to ecologists, engineers, architects and landscape architects. It has been implemented very successfully worldwide and been effective in its way of managing water but also contributing significantly to the production of some truly innovative and outstanding design as well as creating areas of ecological value.

So how can you manage rainwater on a smaller scale in your own garden?

Nigel Dunnett, Professor of Planting Design and Vegetation Technology, and Director of the Green Roof Centre at the University of Sheffield is an expert in rain gardens and small scale rainwater management features. His research has looked at innovative approaches in planting design and landscaping that serve to store, collect and infiltrate rainwater runoff. Examples include the use of storm water or through flow planters, which are essentially raised, planted beds at the base of buildings that can take runoff water directly from roofs or adjacent areas of hardstanding.

The key to Dunnett’s research is that it can be replicated on a small scale in one’s own garden and can be just as effective in terms of its aesthetic and ecological value, particularly in urban areas.

Other approaches to managing rainwater include reducing runoff from hard surfaces, such as driveways and patios, by using permeable paving that allows water to soak directly into the ground. Roofs on sheds and garages or any external outbuildings in the garden could have green roofs installed. Furthermore, you could use Dunnett’s techniques of creating rain gardens and create a truly sustainable garden that works with nature and not against it.

Nigel Dunnett was a recent speaker with the University of Bristol Botanic Garden Friends’ Lecture series.