Secondary site factors

Drainage and Hydrology

Plants vary considerably in their ability to tolerate drought or water-logging. The seasonality of flooding or drought on a site also has a big effect on plant communities, and is quite a complex subject.

Wet soils: From a practical point of view wetland areas if not overloaded with nutrients from adjoining land can produce valuable and diverse habitat and developed and can be sown with a species selection such as our Pond Edge mix EP1. The kinds of plants that establish readily from seed tend to be marginal plants rather than true aquatics: they possess a degree of adaptation to flooding and waterlogging but do not need to be in water to grow. Seasonal flooding may have practical implications for timing of sowing and establishment: this may typically favour sowing in spring to get good establishment before the winter rains.

Drought prone soils usually develop characteristic plant communities. Drought can be caused by soils that drain feely (like sands) and cannot hold moisture (eg low in organic matter). Drought can also occur where the depth of soil is very shallow (as in green roof schemes)  and cannot hold enough water in reserve between showers (particularly in drier parts of the UK). Plant species that cope with surface drought by deep rooting can survive in the first situation, but may not cope where the roots are restricted and cannot grow to find water. In the latter case plants which seed freely and can regenerate from seed after drought (like annuals) can avoid drought in this way.

Sowings on dry sites are usually more successful in autumn giving a longer period for root establishment ahead of droughts in summer. 

Shade and Tree cover

Apart from the obvious effect from shading, trees can also effect ground vegetation through their roots taking moisture, and from autumn leaf-fall which smothers plants and prevent seedling growth. Mixtures of species suitable to these areas like EW1 woodland mix can be sown  Because of the effeccts of trees establishment of sown species may take longer and be more patchy than sowings in the open and this should be taken into account when devising schemes. Long established tree and shrub cover may also cause localised soil enrichment either directly from leaf fall, or as in old parkland as a result of cattle congregating beneath - such areas are best avoided if possible.

Steep slopes and banks

Wild flower mixtures can produce good results on embankments, the additional drainage and shallow soils from years of soil slippage sometimes gives better results than comparable sowings on the flat. The results obtained from a sowing may vary depending on whether the slope faces North or South.

Initial establishment on steep slopes can be tricky as seed is prone to washing off in heavy rain or being exposed to drought in summer.