Seed of herbaceous plants may be either dormant or non-dormant. Dormancy is the condition when the seed is capable of germination but fails to do so when provided with the appropriate conditions. If this phenomenon is not considered when selecting species for seed mixes, low levels of establishment are likely. A detailed discussion of seed dormancy is beyond the scope of this text but can be found in Baskin and Baskin (2001). A categorisation of dormancy is given in terms of landscape practice in Table 6.11.
Non-dormant species germinate in moist soil as soon as they experience high enough soil
Table 6.10. A prairie seed mix formulated by the author for the Eden Project, Cornwall
Number Typical Desired g/seed/m2 in Total amount
of seed percentage of field plants order to of seed
* Based on previous performance in field experiments.
Table 6.11. Seed dormancy in commonly cultivated herbaceous plants (data derived from Atwater 1980; Rock 1981; Baskin and Baskin 2001; Jelitto 2002; Prairie Nursery 2002; plus the experiments of the author)
Leucanthemum vulgare Lychnis chalcedonica Origanum vulgare Papaver orientale Primula (sikkimensis group)
Primula denticulata Sanguisorba officinalis Solidago rigida Thalictrum aquilegifolium
* Double dormant, requires warm then cold then warm cycles to germinate.
temperatures and are generally straightforward to establish by field sowing. Most annuals are nondormant as dried seed; some species demonstrate dormancy immediately postharvest but this disappears in dry storage. The most unreliable species for field sowing are generally either those with deeply dormant seed (see Table 6.11), or non-dormant with erratic germination. In both of these cases (even after treatment for dormancy), the percentage of seedling emergence tends to be low and extended over a period of time. On infertile sites with low numbers of weed seedlings, late-germinating seedlings may survive. On most fertile, weedy sites, these are eliminated as a result of competition for light with larger adjacent seedlings. Exceptions to this are species such as Primula veris and Stachys officinalis seedlings, both of which are highly shade-tolerant and unpalatable to slugs, and continue to appear up to two years post-sowing.