Introduction

Waterlogged soil in winter and dry soil in summer is a problem for plants. Wet soils begin to deprive the roots of oxygen, causing them to die. At the other extreme, drought means as moisture is lost through plants’ leaves and stems, they also wilt, desiccate and die. Winter wet when plants are dormant is less damaging than spring flooding when plants’ roots start to respire.

According to climate experts, more frequent and more sudden extremes of wet and dry are predicted for the future. During autumn-winter 2014, the RHS surveyed horticultural professionals and the wider gardening public to find out which plants they have experienced as being able to cope with wet winters and dry summers.

The list is a starting point and complements the field research and lab-based work the RHS Science teams undertake. The survey extends existing RHS Gardening Advice information, experience and desk research.

Practical considerations

There are a few steps you can take to improve drainage on poorly drained soils including:

1. Add organic matter such as well-rotted farmyard manure or garden compost. This is the most important of all the techniques, whatever your soil type. Organic matter improves soil structure by creating air spaces and what is termed a ‘crumb’structure.
2. Install drainage.
3. ‘Mound’ plant trees. By planting onto a mound 25cm (10in) at its middle, drainage can be greatly improved. To make watering easier in summer, especially in the establishment year, ensure the top of the mound is slightly saucer-shaped.
4. Create raised beds. These allow roots to be raised above the surrounding water table.
5. Don’t risk more tender plants if your garden is cold as well as wet. Check hardiness ratings when selecting.
6. For sudden large amounts of water running off buildings to hard surfaces, or where seasonal flooding occurs, consider creating a rain garden.
7. Use plants that self-seed. Although short-lived in themselves, their ability to self-seed gives them a certain permanence.

Suitable plants

This list is the result of asking gardeners their experiences of which plants have proven tolerant of sitting in water for at least a week in winter and then drying out in summer. It is worth bearing in mind that a number of other conditions may exist, such as shade, frost pockets and whether the water is oxygenated (flowing).

The list includes the plants that are most reported as being tolerant. Others may be as tolerant, but less widely grown.

Cultivars have been chosen for their RHS Award of Garden Merit (AGM) status where possible. Otherwise, good cultivars that are widely available have been selected.

Trees

Amelanchier 'Robin Hill’
Betula utilis var. jacquemontii 'Silver Shadow' AGM
Cratageus laevigata ‘Paul’s Scarlet' AGM
Magnolia grandiflora
Malus (crab apple) 

Shrubs

Buddleja davidii ‘Nanho Purple’ AGM
Cornus alba ‘Sibirica AGM
Fuchsia magellanica ‘Riccartonii’ AGM
Hydrangea arborescens ‘Annabelle’ AGM
Physocarpus ‘Diablo’ PBR AGM
Rosa rugosa ‘Roseraie de l’Hay’ AGM
Viburnum opulus ‘Roseum’ AGM

Herbaceous perennials

Alchemilla mollis AGM
Astrantia ‘Ruby Wedding’
Geranium Rozanne = 'Gerwat' AGM
Geum ‘Mrs J. Bradshaw’ AGM
Hemerocallis ‘Burning Daylight’ AGM
Hosta (Tardiana Group) ‘Halcyon’ AGM
Iris sibirica ‘Tropic Night’ AGM
Iris unguicularis
Lythrum salicaria ‘Robert’
Persicaria affinis ‘Darjeeling Red’ AGM
Phlox paniculata ‘White Admiral’
Stachys byzantina
Verbena bonariensis AGM

Grasses

Calamagrostis brachytricha AGM
Miscanthus sinensis ‘Kleine Fontäine’ AGM

Annuals and short-lived perennials that tolerate wet and dry soils due to their capacity to self-seed:

Aquilegia vulgaris
Borago officinalis
Digitalis purpurea
Knautia macedonica
Verbena bonariensis AGM