Research matters... germination of Penstemon

Although established Penstemon cultivars are normally propagated by cuttings, there are occasions when propagation by seed is apparently necessary. The seeds of many Penstemon species are dormant initially and so will not readily germinate.

In the experiments reported below, fresh seeds of Penstemon digitalis 'Husker Red' were soaked for 24 hours in solutions of gibberellic acid (GA3) ranging from 0mg to 1,500mg of GA3 per litre. The seeds were then placed on moist filter paper in glass dishes in a dark growth chamber at a temperature of 21.3 degsC.

All treatments with gibberellic acid increased seed germination relative to the control but the highest percentage germination and the fastest speed of germination were obtained with 1,000mg GA3 per litre.

In other experiments, the percentage germination was reduced by placing the gibberellin-treated seeds in a heated greenhouse with fluctuating day and night temperatures. It seems likely that constant temperatures and darkness benefit germination of GA3-treated Penstemon seeds.

- The authors also reach this conclusion, although it is not supported by the way the data are presented in Table 3. That is because the column labels have been accidentally swapped over, ie for "Greenhouse" read "Growth chamber" and vice versa, as the authors now acknowledge.

Gibberellic Acid Promotes Seed Germination in Penstemon digitalis cv. Husker Red by Machedo de Mello, Streck, Blankenship and Paparozzi (2009). HortScience 44 (3): 870-873. Members of ISHS can view HortScience from the website

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