Echinacea purpurea 

Technical Write-Up

The published peer-reviewed experimental evidence is substantial for this species with regard to seed dormancy and germination behaviour. Qahhorov (2024) studied fresh seeds after harvest and without any cold stratification yielded only 30% germination, suggesting dormancy of most seeds at dispersal. Li et al (2007) used fresh seeds (3 months after harvest), which yielded 63% germination without cold stratification. Hasan Beigi et al (2021) tested the germination of fresh seeds (2 weeks old, stored at 4C in a dried state) where GA3 improved germination above controls. Aghilian et al (2014) used relatively fresh seeds and achieved 70% germination without cold stratification. It is readily apparent that seeds exhibit a non-deep physiological dormancy which is dissipates rather quickly with after-ripening, at least in half the seeds of a given batch. Typical germination results are at least 50% for relatively fresh seeds (i.e., less than 6 months old) without cold stratification, suggesting that a third or half of seeds in a given batch are non-dormant or conditionally dormant and require no treatment to induce germination.

Li et al (2007) scarified seeds to test for a physical dormancy component, but this did not yield higher germination. They found that the seed coat is likely responsible for enforcing a physiological dormancy, as its removal promotes germination. Certainly there is overwhelming evidence that cold stratification improves germination of seeds regardless of their age (Li et al, 2007; Hitchmough et al, 2004; Ramos et al, 2018; Romero et al, 2005; Shalaby et al, 1997; Li, 1998; Fateh et al, 2012; Wees, 2002; Yurteri et al, 2021; Bratcher et al, 1992; Bratcher et al, 1993; Aghilian et al, 2014; Schwilk and Zavala, 2012).

With regard to the level of physiological dormancy exhibited by the seeds, it is noted that seeds exhibit after-ripening with prolonged dry storage, they respond to GA3, and they generally require short durations of cold stratification to break dormancy of most of the seeds. The evidence is as follows, and it suggests a non-deep level of physiological dormancy.

With regard to the after-ripening behaviour of the seeds, it is noted that several studies have shown that commercially sourced seeds (i.e., seeds which are stored at room temperature for long periods) generally germinate better than wild collected seeds (Qu et al, 2005; Romero et al, 2005; Hassell et al, 2002; Hassell et al, 2004; Qu LuPing et al, 2005). Also, seeds that were stored for longer periods have been observed to germinate fairly well without any cold stratification (Qu et al, 2005; Hassell et al, 2002; Wartidiningsih and Geneve, 1994; Ermis et al, 2025; Parmenter et al, 1996; Yurteri et al, 2021; Aghilian et al, 2014; Hassell et al, 2004; Zarghani et al, 2014; Belyaeva and Konusova, 2014).

With regard to chemical promoters of germination, it has been observed by many studies that GA3 or GA4+7 promote strong germination (Li et al, 2007; Yousefi et al, 2021; Pill and Haynes, 1996; Maslova et al, 2020; Tuncturk et al, 2019; Li, 1998; Ansari et al, 2016; Ansari et al, 2016; Fateh et al, 2012; Hasan Beigi et al, 2021; Ermis et al, 2025; Kochankov et al, 1998). Also, KNO3 has been found to promote germination above controls (Ansari et al, 2016; Fateh et al, 2012).

With regard to the duration of cold stratification required to break dormancy of the majority of seeds in a given batch, it has been shown repeatedly that as few as 2-4 weeks is required to release dormancy of the vast majority of seeds (Li et al, 2007; Hitchmough et al, 2004; Ramos et al, 2018; Romero et al, 2005; Shalaby et al, 1997; Fateh et al, 2012; Wees, 2002; Yurteri et al, 2021; Bratcher et al, 1992; Aghilian et al, 2014). Longer cold stratification periods have shown an increased germination overall (Fateh et al, 2012), but the majority of seeds in a given batch respond very well to just 2-4 weeks of cold stratification.

The combined evidence around after-ripening, GA3 responsiveness, and brief lengths of required cold stratification, suggest a non-deep level of physiological dormancy.

To grow from seed, it is noted that fresh seeds will likely still germinate at least 50% if provided the right temperature and moisture. At least a third to half of seeds in any given batch will be non-dormant. However, the gardener should always maximize germination, and the germination of stronger plants is always encouraged – and therefore the cold stratification of seeds is strongly advised. As noted above, 2 to 4 weeks is often the suggested cold stratification treatment (Li et al, 2007; Hitchmough et al, 2004; Ramos et al, 2018; Romero et al, 2005; Shalaby et al, 1997; Fateh et al, 2012; Wees, 2002; Yurteri et al, 2021; Bratcher et al, 1992; Aghilian et al, 2014) and which will provide at least 75% germination. However, if the gardener is using wild-harvested seeds (or seeds harvested from her garden), they may have a stronger dormancy than those purchased commercially. Fateh et al (2012) tested various lengths of cold stratification and found that 12 weeks produced the highest germination – and which is suggested. If the gardener is short on time, 4 weeks should provide sufficient results, however. The temperature studied for cold stratification has been around 4C (40F) as per the previoulsy mentioned studies. There is no evidence that colder or warmer temperatures are more or less effective. It might also be noted that if ambient light is provided in the daytime for the cold stratification, that this may provide a minor improvement in germination (Romero et al, 2005); however this is usually not practical to achieve (nor practically important). Still, it must be mentioned.

After cold stratification, the optimum temperature for germination has been well studied and by many researchers. The studies are in high agreement that a temperature around 25C (80F) is the optimum temperature for germination (Li et al, 2007; Qu et al, 2005; Romero et al, 2005; Shalaby et al, 1997; Hassell et al, 2002; Fateh et al, 2012; Ermis et al, 2025; Kochankov et al, 1998; Yurteri et al, 2021; Aghilian et al, 2014; Hassell et al, 2004; Zarghani et al, 2014). Seeds will not germinate well below 20C (~70F) (Hassell et al, 2002; Hassell et al, 2004; Zarghani et al, 2014), and neither will they germinate well above 35C (~95F) (Hassell et al, 2002; Hassell et al, 2004). There is no evidence that seeds cycle in and out of primary/secondary dormancy with excessive heat, therefore the gardener does not need to be too careful on providing heat. It is especially noted that 30C (~90F) has been shown to be equally effective as 25C (80F) (Li et al, 2007; Ramos et al, 2018; Hassell et al, 2002; Ermis et al, 2025).

Studies show that light does not promote germination compared to darkness (Romero et al, 2005; Wartidiningsih and Geneve, 1994; Zarghani et al, 2014; Belyaeva and Konusova, 2014), although some studies show a minor improvement in germination with light (cf. Li et al, 2007) but such benefits are mild. Seeds can therefore be covered to ensure better contact with moist substrate. The induction period for seedling emergence is typically around 5-7 days if 25C (80F) is used as the incubation temperature (Li et al, 2007; Ramos et al, 2018) but shorter induction periods are known to happen (Romero et al, 2005; Fateh et al, 2012; Zarghani et al, 2014).

With respect to dried seeds, it is clear that seeds experience after-ripening after prolonged dry storage, but it is uncertain how long seeds should be kept dry for this to be meaningful. Seeds that have been stored at room temperature for 6 months or longer will likely not benefit from cold stratification and can simply be sowed at 25C (80F), with or without light. There is some evidence that 28C (~83F) is more effective for older seeds than fresh seeds (Hassell et al, 2004), otherwise they will behave the same in being indifferent to light and emerging in 2-7 days.