The natural spread of woodland field layer plants will depend on various factors:
- Soil type. On agricultural soils which have been cultivated for many years there will be high fertility and a poor seed bank of native woodland plants. Growth of the less desirable plants such as nettles, docks, brambles and thistles is likely to be prolific.
- Proximity of other woodlands. If there are existing woods, copses or hedgerows adjacent to the new planting, there is a good chance of woodland plants spreading into the wood. Where possible, abut new planting to existing trees.
- Closure of the woodland canopy. Woodland plants cannot compete where there is sufficient light for grasses to grow. As the canopy closes and leaf litter builds up the conditions become suitable for woodland plants to grow.
- Size of the woodland area. A woodland smaller than about 40m x 40m, or a strip narrower than about 15m, will never create sufficient shade to allow the growth of a true woodland flora. planting shrubs along the edges will help reduce light levels and may allow some woodland plants to grow.
- Understorey shrubs. If these are very dense, they will make the ground too shady for the growth of a diverse ground flora.
Introducing woodland flora
Where new woodlands are isolated from natural sources, woodland flora can be introduced by sowing direct, by planting bulbs or tubers, or by planting pot-grown plants. However plants are introduced, it’s important that all seeds, bulbs, tubers or plants are of native provenance, which means that they originate from native British sources. Seeds or plants of British native provenance bought from nurseries and seed suppliers can be directly traced back to seed collected in the wild. These original seeds are used to produce stock plants in the nursery, from which seed and plants for retail sale are produced. Plants of local provenance, grown from seed originally collected from local wild plants, are even better, as many species have genetically distinct varieties which exist only small distances apart. Only buy plants from reputable nurseries who can guarantee that their plants, bulbs or tubers have been legitimately grown, and have not been dug up from the wild.
Alternatively, as with tree seeds, you can collect your own seed, provided you have permission to do so from the landowner. The seed can then either be sown direct onto the site, or sown to produce plants for planting out. Note that under the Wildlife and Countryside Act there over 60 species of native wild flowers from which it is illegal to gather seed, due to the rarity of the species. These include some woodland plants, including some orchids. It would be unusual to find these plants, but if in doubt, don’t collect.
Woodland plants should never be dug up from existing sites, even with permission from the landowner. Under amendments to the Wildlife and Countryside Act, the digging up of some species, including bluebells, will become illegal. The Bluebell Recovery Project, sponsored by Landlife and the Mersey Forest Project, is working to protect existing bluebell woodlands from bulb thefts by creating a sustainable supply of native bluebell bulbs for legitimate sale in the future.
Woodland ground flora can be divided into three groups (Peterken, 1981). Some examples from each group are given below.
Group 1:
These are species normally associated with ancient woodland sites. Under natural conditions most of these produce little seed, and are slow to spread and colonise, which is why they are mainly limited to ancient woodland sites. Of the three groups, these are most exacting about site requirements, needing a closed canopy, the presence of leaf litter and absence of competition. Most of these species are available commercially as either seed, bulbs or plants. Ensure that bluebells are the species listed, and not the Spanish variety Hyacinthoides hispanica.
Bluebell Hyacinthoides non-scripta syn. Endymion non-scriptus
Dog’s mercury Mercurialis perennis
Lesser celandine Ranunculus ficaria
Moschatel Adoxa moschatellina
Ramsons Allium ursinum
Wood anemone Anemone nemorosa
Wood sorrel Oxalis acetosella
Group 2:
Fast-colonising species of recent woodlands and woodland edges. These are common at woodland edges, and persist at lower densities within the woodland in light shade. They tend to produce large quantities of seed, and are able to rapidly colonise bare ground. They are available commercially and are easy to grow from seed. Species include:
Ground ivy Glechoma hederacea
Hedge woundwort Stachys sylvatica
Herb robert Geranium robertianum
Red campion Silene dioica
Sweet woodruff Galium odoratum
Wood avens Geum urbanum
Group 3:
These include a large number of species which are common in woodland edges and hedgerows, but which are also common in other habitats. They produce large quantities of seed, and are easy to grow. Species include:
Betony Stachys officinalis
Cow parsley Anthriscus sylvestris
Foxglove Digitalis purpurea
Hedge bedstraw Galium mollugo
Hemp agrimony Eupatorium cannabinum
Meadowsweet Filipendula ulmaria
Introducing ground flora into new woodlands is not easy. Wild flowers are difficult to germinate and grow as they are very exacting in their requirements, unlike most garden flowers, which have been selected to tolerate a wide range of conditions and treatments.
you are unlikely to have success simply by scattering seed within the woodland, even if ground conditions look suitable. The seed of most woodland wild flowers needs vernalisation, or the action of winter frost, to make it germinate the following spring. During this time, much of the seed will be eaten by small mammals, with primrose and violet seed especially palatable to mice. Early spring sowing after cold treatment in a fridge may be possible, but the use of container-grown plants is usually better.
Use standard propagation techniques to germinate the seed in cells, trays or pots, and then grow them on until they are large enough to plant out. Species vary in their ease of germination, and experience in growing plants from seed is useful if you are going to try this method. The seed of most woodland plants should be sown in autumn, protected from mice and stored outside during the winter. Bring the trays into gentle warmth in February, and then prick out the plants into pots or cells as soon as the true leaves start to show. Grow them on during the summer, and plant out in the autumn.
Alternatively, some of the plants listed above, and other suitable species, are available as cell-grown plants or ‘plugs’. These are plants grown in cells, which are despatched from the nursery as close-packed plants with rootballs of compost, which have been removed from the cells in which they were grown. larger plants may be available in pots. The size of plant and method of despatch and packing will vary with the nursery, the season and the particular species.
Depending on the level of care you can give in the field, it may be advisable to grow on wildflower ‘plugs’, until they are larger, sturdier plants which can compete more successfully. They can be grown on either in pots, or in a nursery bed, which in effect can become your stock bed from which you produce plants for the wild.
Planting out
Try to obtain the plants in spring and plant out as soon as conditions are suitable, preferably with the soil moist but beginning to warm up so that plants establish quickly. Choose suitable sites for the species, taking particular note of their requirements for shade.
Species from group 1 (above) should only be planted under closed canopy, where there is already bare ground. Choose sites which will not be trampled, perhaps under low spreading branches of trees or shrubs and away from paths and public access areas. Plant at about 9 plants per square metre, with the aim of encouraging the plants to form a clump from which they can spread into the surrounding woodland floor. For each plant, dig a larger hole than the size of the plug, incorporating some well-rotted leaf litter if the soil is lacking in organic matter. If possible, water the plants in well. Cover the surface of the plug with soil or leaf litter, otherwise the compost in the plug tends to dry out.
Plants from groups 2 and 3 should spread more quickly, and so can be planted at about 5 per square metre. choose sites which are too shady to support the growth of grass, but which may support shade bearing plants such as ivy, nettle and bramble. Clear a patch a bit larger than the area you want to plant, and keep weeded until established.
Mark the locations of the planting areas on your woodland plan, and on the ground with pegs or stakes, so that you have a record of them, and can re-locate them to check on their progress and weed as necessary. Keep a look out for desirable wild plants which may appear, and don’t necessarily weed out everything. As plants establish, you can divide clumps and replant in other parts of the woodland.
Muntjac deer can cause a lot of damage to ground flora, and as with young trees, may target nursery plants. Rabbits can also be troublesome. Clumps of plants can be protected with loose piles of cut, dry brambles or with a ‘cage’ of chicken wire or similar. Old treeshelters cut into shorter lengths may also be effective. If browsing pressure from deer is very severe, it may be advisable to delay planting plans until effective deer control measures have been taken.
Bulbs
The woodland flora includes many plants which grow from bulbs. These are adapted to woodland conditions, as the bulbs produce an early burst of growth, flowering and reproduction before the canopy closes over in late spring. Bulbs are best planted during the autumn, as soon as you obtain them from the supplier. Ensure that any bulbs you buy are produced in nurseries, and are not taken from the wild. Only plant into the woodland once the canopy has closed, and grass growth has been eliminated by lack of light. A guide to planting is given below:
Bluebells (Hyacinthoides non-scripta)
2-3 bulbs in holes 10cm (4”) deep, 60cm (2’) apart
Lesser celandine (Ranunculus ficaria)
2-3 bulbs in holes 5cm (2”) deep, 15cm (6”) apart
Snowdrops (Galanthus nivalis)
6 bulbs in holes 5cm (2”) deep, 30cm (1’) apart
Wild daffodils (Narcissus pseudonarcissus)
2-3 bulbs in holes 5cm (2”) deep, 30cm (1’) apart
Ramsons (Allium ursinum)
3-4 bulbs in holes 5cm (2”) deep, 30 cm (1’) apart
Wood anemone (Anemone nemorosa)
2-3 rhizomes, horizontally, 5cm (2”) deep, 30cm (1’) apart
