Seed dormancy

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

per g

establishment*

per m2

achieve this

required (g/m2 x total area of 1,250 m2)

Aster azureus

2,877

15

15

0.03

43.4

Aster laevis

1,684

8

10

0.07

92.8

Echinacea

pallida

175

40

10

0.14

178.1

Echinacea

purpurea

232

30

15

0.22

269.9

Euphorbia

corollata

351

20

10

0.14

178.1

Helianthus

mollis

270

40

5

0.05

57.8

Helianthus

occidentalis

456

20

10

0.11

137.1

Liatris aspera

474

20

10

0.11

132.0

Liatris

pycnostachya

421

15

10

0.16

197.9

Petalosporum

purpureum

714

15

10

0.09

116.7

Ratibida

pinnata

947

30

10

0.04

44.0

Rudbeckia

1,614

5

10

0.12

154.9

subtomentosa

Silphium

integrifolium

140

40

2

0.04

44.5

Solidago rigida

1,614

40

10

0.02

19.4

Solidago

speciosa

3,684

20

10

0.01

17.0

Total:

147.00

1.35

1,683.63

* 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)

Highly dormant

Slightly dormant

Dormant, physical

Aconitum

Echinacea pallida

Amorpha canescens

Astrantia

Helianthus

Baptisia

Deschampsia cespitosa

Primula japonica

Lupinus

Molinia caerulea

Primula pulverulenta

Petalosporum purpureum

Paeonia*

Rudbeckia fulgida

Stipa

Persicaria bistorta

Silphium

Thermopsis

Primula veris

Solidago speciosa

Pulsatilla vulgaris

Veronicastrum virginicum

Rhinanthus minor

Stachys officinalis

Trollius

Non-dormant

Non-dormant, erratic

Aster (most)

Aster laevis

Buphthalmum

Euphorbia

Campanula (most)

Geranium

Centaurea scabiosa

Inula ensifolia

Echinacea purpurea

Linum narbonense

Grasses (most meadow)

Malva moschata

Grasses (most prairie)

Ranunculus acris

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.