Good ground preparation is the best way to maximise the number of seeds that successfully make the precarious journey from germination to mature plant. Before sowing wild flower seeds the most important tasks are:
· to create space by removing unwanted vegetation and ‘weeds’ which may compromise results
· to create conditions in which seedlings can establish and grow
In practice there are two main routes to establishing wild seeds and mixtures:
1 . Sowing into bare soil cleared of vegetation
Generally the most successful way to establish wild flowers and grasses from seed is to sow into a clean seedbed that has been first cleared of all weeds and other vegetation and then cultivated to produce optimum conditions for germination.
2 . Sowing into gaps created in existing vegetation
Seed sown into gaps in existing vegetation will grow, but more slowly and less reliably as a result of competition from well established neighbours. Where site assessment reveals that the existing vegetation is worth preserving this approach, although slower, could be more appropriate.
Sowing into bare soil
In open ground, control of ‘weeds’ can be achieved by repeated cultivation to exhaust weeds (fallowing). Recently cultivated land with annual weeds can be cleared for sowing in a few weeks. Neglected plots which contain perennial weeds with extensive root systems (eg couch grass) may take more than one season to complete. It does not pay to rush this process as it is very difficult to deal with residual perennial weeds after sowing. Unwanted vegetation can be cut back and removed from site or chopped up to be incorporated during cultivation.
Cultivate the soil to sufficient depth to bury remaining trash and to alleviate compaction, then rake or harrow and roll to produce a fairly fine, firm surface. The finished seedbed should be firm enough to walk on without leaving impressions. As the area will be mown at a later stage the finished surface should be free of obstructions such as large stones or bricks, and free of deep ruts or ridges. The “stale seedbed technique” can work well for annual weeds whose seeds will remain in the soil after clearance. This method involves preparing a seedbed then delaying sowing to allow a flush of weed seed germination from the surface layers. This flush of weeds is then killed, by shallow cultivation, before sowing your seed mixture onto the cleaned “stale” seedbed – the surface of which now has a reduced weed seed burden.
Sowing into gaps created in existing vegetation
The most suitable sites will be of low to medium fertility, with a fine sward structure free of perennial weeds and vigorous grasses. Preparation should begin by implementing an appropriate management regime at least one year before seeding. This will include rigorous mowing or grazing to reduce the vigour of coarser grasses and develop a better sward structure.
Weed control: Problem perennial weeds in grassland should be controlled by selective measures such as targeted scything or mechanical removal.
Mow/graze: The sward should be cut or grazed hard in the autumn; aim to keep the grass short (30-50mm). Graze or mow both before and after seeding as needed.
Create gaps across the site with exposed soil for seed to germinate in. This can be achieved by:
• autumn/winter grazing with stock (their hooves break open the sward)
• mechanically by harrowing or raking, aiming to expose up to 50% bare soil
Mechanical disturbance needs to be severe to work (40-50% destruction) as grass can recover and grow back very rapidly. Disturbance and seeding is best applied at a time when grass growth is in decline as in autumn. In spring, grass growth and recovery is too rapid and will shade out seedlings. Once ground preparation has been completed, seed can be sown by surface broadcasting. Rolling is not usually needed for autumn applications as the weather will settle the seed to the soil. Hooves of grazing animals, where present, may help firm in seed. Yellow rattle established in a sward will often help other sown seed establish by leaving gaps at the end of each growing season as the annual yellow rattle plants die away.
Sowing into woodland and other habitats
Gaps can be created by digging out patches within the vegetation. Take care around established trees and hedges as cultivations can be damaging to tree and shrub roots – only shallow cultivations are safe here.