Thursday, 19 November 2015

Garden Challenges: Water logged gardens and bogs!

This subject seems appropriate given the weather we are having. Wet, waterlogged, boggy areas in the garden are usually caused by a high water table or bad drainage, usually because the soil is clay. An easy way to assess the cause and then be able to improve it is to dig a hole two feet deep. Leave covered over night, if there is water in the bottom, you have a high water table. If it is dry, fill with water and see if it drains away over night. If the hole has contained the water this suggests a clay soil, usually compacted and so not allowing natural drainage.

Pond and bog garden, Kalmthout Arboretum, Belgium

If the water table is high there isn't a lot can be done, and you need to garden according to the conditions. It does mean you can consider creating a bog garden, which wild life will love and you can grow a large selection of water and moisture loving plants. Another solution to wet soil is to build raised beds. These can add a great feature to your garden and give the plants drainage and good growing medium as you can choose what mix of compost, soil, etc to fill the raised beds with.

Raised beds at Woodside, Jedburgh

If the problem is compacted clay soil and poor drainage there are a couple of solutions. One is the more expensive and involved process of digging trenches and installing land drains and gravel to take any water away, remember you must have somewhere for it to drain into. The RHS has a good article here about installing drainage in gardens. You could stick with raised beds which means you don't have to disturb the existing soil. Or you can dig over the soil adding in plenty organic matter which chemically makes the clay clumps smaller. Grit and sand are often suggested, but this is a back breaking job which isn't always effective.

Mixed border in my last garden with a high compost content which has
vastly improved the soil conditions

In my last garden, which I created over 15 years, I added home made compost to the borders every year. The soil there was clay and over those 15 years I saw a significant improvement to the soil structure and improvement in drainage. It became a much more open, workable medium and the plants benefited too. I will be doing the same here in the nursery gardens as we develop them, as the soil here is clay and prone to surface water lying on compacted areas. 

Lythrum and bull rushes at Inveresk Gardens

As you can see this type of garden problem usually involve hard physical work, but the results are worth it as you have a usable garden and can grow a wider variety of plants. If you decide to work with the wet areas you have, what can you grow to give you an interesting garden? Many plants will tolerate wet or waterlogged soil for some of the time but not continually, but there are some plants that will grow happily in this situation and many of which are available in the nursery here.


Flowers or Darmera peltata

Darmera peltata in my last garden, I grew this on the edge of a bog garden and it was happy when there was
enough water to raise the water level over it's roots for a while


Equisetum hymale will grow in or out of water


Iris pseudocorus 'Variegata' will grow in water or on the margers of
a pond


Filipendula will be happy in damp soil on the edges of a bog garden
Gunnera in Inveresk Gardens, likes damp soil

Cornus alba 'Sibirica' will take wet soil


Hostas and Primulas love damp to wet soil, but not waterlogged

Matteucia struthiopteris in Dawyck Gardens, a great fern for damp soil

Osmunda regalis will take damp soil, with its dark stems and lush leaves, it is worth a place in the garden


Ferns
Matteucia struthiopteris - 'Ostrich fern'
Osmunda regalis - 'Royal fern'

Grasses
Carex
Phalaris

Herbaceous
Aruncus - 'Goats beard'
Astilbe
Caltha - 'Kingcup' or 'Marsh marigold'
Darmera peltata
Epilobium - 'Willow herb'
Eupatorium
Filipendula - 'Meadowsweet'
Geum
Gunnera mannicata
Hemorocallis - 'Day lily'
Hosta - 'Plantain lily'
Iris Pseudoacorus - 'Flag iris'
Iris Sibirica - 'Siberian iris'
Ligularia
Lythrum - 'Purple loosestrife'
Lysimachia
Monarda - 'Bergamot'
Polygonum - 'Knotweed'
Primula
Rheum - 'Ornamental rhubarb'
Rodgersia
Sanguisorba
Symphytum - 'Comfrey'
Trollius - 'Globe flower'

Shrubs
Cornus - 'Dogwood'
Hippophae rhamnoides - 'Sea buckthorn'
Neillia thibetica
Physocarpus
Sambucus - 'Elder'
Salix - 'Willow'
Viburnum opulus - 'Guelder rose'

Trees
Alnus cordata - 'Italian alder'
Amelanchier canadensis - 'Snowy mespilus'
Metasequoia - 'Redwood'
Sorbus aucuparia - 'Rowan' or 'Mountain ash'
Taxodium distichum








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