Establishment by sowing in situ

Choice of communities and species

As has been discussed in the section ‘Types of herbaceous plant communities: habitat stereotypes’, basing choice of communities and species upon habitat stereotypes, as presented in Tables 6.1 to 6.6, helps to arrive at plants that are broadly compatible with a landscape site and one another (Figure 6.9). With native species it is possible to buy seed as individual species or pre-formulated as mixes for various soil conditions. Most practitioners lack the knowledge and experience to make up their own mixes, and buy pre-formulated mixes. Whilst these are satisfactory for general use they suffer from the following disadvantages.

Many provide a mix of grasses and forbs in the ratio 4:1 (by seed weight). This is fine if you want a very grassy vegetation to provide quick cover, but is less satisfactory where a meadow dominated by colourful forbs is desired. In our experience, most forbs flower earlier in life and more abundantly when sown in the absence of grasses. Some suppliers will provide forb and grass mixes separately.

You are limited to what is offered in terms of species and the relative proportions of these. This is very limiting in terms of producing specific effects, for example dramatic colour combinations or a high density of a specific species.

You can also buy ‘off the peg’ mixes for nonnative species, for example various types of North

Establishment by sowing in situ

6.9

Seeding produces a very naturalistic look, with high densities of species in this prairie sown in Sheffield

Table 6.9. Advantages and disadvantages associated with the main methods of establishing naturalistic herbaceous vegetation

Key advantages Key disadvantages

Подпись: Sowing in situInexpensive, cost of seed < £1.50 m2 Requires specialised skills to weigh out

small quantities of seed, pre-treat seed where required, calibrate sowing equipment

Подпись: Cost of implementation low Produces very fluid, naturalistic effects High densities of plants readily achievable Access to accurate electronic scales is necessary

Most contractors have little experience of establishing vegetation by sowing in situ

Timing of sowing has a major impact upon success. This is not always possible in commercial landscape projects

Complicated planting plans are not required

Can be used on mechanically hostile soils that are difficult to plant

Lower susceptibility of vandalism and, in particular, plant theft

More sustainable, as energy intensive nursery facilities are not required

Essential for annuals and biennials

Successful establishment often requires good control of the germination environment. This is not always possible

Minimal initial impact

Often requires control of slugs for high seedling establishment

Weed control is more complex than with planting

Подпись: Expensive to very expensive for plant materials May require drafting of complex, difficult to follow planting plans Slow and expensive to implement, due to the high density of planting Tends to import nursery weeds into the site Подпись:Planting High-initial impact

Can use particular cultivars

Contractors are more familiar with planting as an establishment technique

Can use mulching to reduce weed invasion

Allows for the use of plants that are highly palatable to slugs as seedlings but not as adults

Can be undertaken at any time of the year given irrigation, etc.

Planting and Allows for reasonably high initial­sowing in impact at relatively low plant situ material and implementation costs

Can use particular cultivars

Allows for the use of plants that are highly palatable to slugs as seedlings but not as adults

American Prairie plant communities, but they suffer from the same problems as the above. The advantage of ‘off the peg’ mixes is that you do not need to know as much about what you are doing, you instruct a contractor to sow at 4 g/m2 and hope for the best. If you want to use sowing more creatively to produce designed naturalistic vegetation, it is necessary to formulate your own mixes.

To do this you need to think through your visual and functional requirements, then formulate a mix to satisfy these. A portable scientific balance (approximate cost £120.00) is essential to weigh out grams of seed. Examples of a successful seed mixes that the author developed for the prairie exhibit at the Eden Project are given in Table 6.10. This

site had to look colourful from July to Autumn, and tolerate the dry, infertile, sandy soil but also the high rainfall climate.