Can germination stimulants help Kentucky bluegrass get started faster?

April 3, 2026

By Xin Xin

Kentucky bluegrass is one of the most widely used cool-season turfgrasses for lawns and sports surfaces, but anyone who has seeded it knows that its establishment can be slow (Folck et al., 2023). Compared to other cool-season grasses, Kentucky bluegrass often germinates gradually and unevenly, which can leave a newly seeded area exposed to weed pressure and slow early cover development (Braun et al., 2022). In our recent work, we asked a simple question: can germination stimulants help Kentucky bluegrass seed get off to a better start?

To explore that question, we evaluated several compounds that have been linked to germination in other species. These included gibberellins (GA1, GA3, GA4, and GA7), karrikins (KAR1 and KAR2), liquid smoke, and combinations of GA4/7 with potassium nitrate (KNO3). Gibberellic acid is a naturally occurring plant hormone that has long been used to help grass seeds break dormancy and germinate more quickly. Different forms of gibberellins are known to play important roles in triggering this process (Fernández et al., 1997). In addition, smoke-related products have shown promise in stimulating germination in dormant seeds (Peterson et al., 2025). Liquid smoke can mimic natural fire signals, while karrikins, which are the compounds found in smoke and ash, have been identified as key drivers of this response (Long et al., 2011). Two seed lots of the Kentucky bluegrass cultivar ‘Tirem’ were used in controlled germination tests.

Line graph showing cumulative germination of Kentucky bluegrass across multiple liquid smoke concentrations over time. Higher concentrations slow germination and reduce final germination in one seed lot, while the second seed lot shows little response except at the highest concentration.
Figure 1. ‘Tirem’ cumulative germination in response to imbibing in different concentrations of liquid smoke. Shaded areas represent a 95% confidence interval.

 

Line graph showing cumulative germination of Kentucky bluegrass treated with karrikins (KAR1 and KAR2) and controls. KAR2 slightly speeds germination in one seed lot, while both treatments show minimal or negative effects in the second seed lot.
Figure 2. ‘Tirem’ cumulative germination in response to imbibing in KARs and controls. Shaded areas represent a 95% confidence interval.

The results suggest that not all treatments were helpful. Liquid smoke generally reduced germination or provided no benefit (Figure 1), and karrikins produced inconsistent responses between the two seed lots (Figure 2). KAR2 slightly increased germination speed in one lot, but neither karrikin consistently improved final germination (Figure 2). These results suggest that compounds reported to stimulate germination in other species do not necessarily translate into reliable improvements for Kentucky bluegrass.

Line graph comparing cumulative germination of Kentucky bluegrass treated with different gibberellins (GA1, GA3, GA4, GA7) and controls. Several gibberellins, especially GA4, increase germination speed in one seed lot, while responses are similar across treatments in the second seed lot.
Figure 3. ‘Tirem’ cumulative germination in response to imbibing in concentrations of GAs and controls. Shaded areas represent a 95% confidence interval.

The most promising results came from gibberellin treatments, especially GA4-related treatments. In one seed lot, GA3, GA4, and GA7 improved germination, with GA4 showing especially early signs of activity (Figure 3). Higher rates of GA4/7 further improved both germination speed and final germination, and the combination of GA4/7 with 0.2% KNO3 produced the strongest response. However, the second seed lot responded much less, and the highest GA4/7 rate reduced germination, showing that treatment effects were strongly seed-lot dependent (Figure 4).

Line graph showing cumulative germination of Kentucky bluegrass treated with GA4/7 alone and in combination with potassium nitrate (KNO3). The combination treatment accelerates germination and increases final germination in one seed lot, with more moderate effects in the second seed lot.
Figure 4. ‘Tirem’ cumulative germination in response to imbibing in combination of GA4/7 and KNO3.Shaded areas represent a 95% confidence interval.

One of the takeaways from this work is that Kentucky bluegrass seed lots can differ dramatically in dormancy and germination behavior. One lot germinated much more slowly and appeared more dormant, while the other showed faster and higher germination overall. That difference likely explains why some treatments were effective in one lot but not the other. These findings suggest that GA4/7, particularly with KNO3, may help improve germination in more dormant Kentucky bluegrass seed lots, while also highlighting the need for future work to identify when these treatments are most likely to be useful in practice.

References

Braun, R. C., Courtney, L. E., & Patton, A. J. (2023). Seed morphology, germination, and seedling vigor characteristics of fine fescue taxa and other cool-season turfgrass species. Crop Science, 63, 1613–1627.

Fernández, H., Doumas, P. & Bonnet-Masimbert, M. (1997). Quantification of GA1, GA3, GA4, GA7, GA8, GA9, GA19 and GA20; and GA20 metabolism in dormant and non-dormant beechnuts. Plant Growth Regulation, 22, 29–35.

Folck, A. J., Bigelow, C. A., Jiang, Y., & Patton, A. J. (2023). Genotypic variation in germination rate, seedling vigor, and seed phenotype of Kentucky bluegrass cultivars. Crop Science, 63, 3065–3078. 

Long, R. L., Stevens, J. C., Griffiths, E. M., Adamek, M., Powles, S. B., & Merrit, D. J. (2011). Detecting karrikinolide responses in seeds of the Poaceae. Australian Journal of Botany, 59, 609–619. 

Peterson, N., Gardner, W., & Fraser, L. H. (2025). The effect of smoke-water on seed germination of 18 grassland plant species. Fire, 2025, 8, 382. 

Tags
Xin Xin
Kentucky bluegrass
stimulants