When germinating seeds one of the main things to consider is dormancy. Many species have a form of dormancy which is caused by “conditions within the seed that prevent it germinating.” Dormancy can be split into two main types. The first is exogenous dormancy: this category covers factors outside the embryo that prevent the seed germinating. They are often physical factors such as hard seed coats. In this post though, we will not be discussing exogenous dormancy.
Today it is the other type of dormancy I am concerned with: Endogenus. This type of dormancy is “caused by conditions within the embryo.” Most typically, these are hormone-based inhibitions that prevent the embryo from actually sprouting, e.g. absissic acid (ABO) concentrated in high enough levels can counteract growth promoting enzymes like gibberellins. This is known as a physiological state of dormancy.
Physiological dormancy, despite how complex it sounds, is one of the most common seed dormancy types. Most physiological dormancy is broken with hot/cold stratification (the alteration of temperature over a period of time), which you may be familiar with from common seed packet instructions. Cool temperatures allow oxygen to pass through certain membranes and enter the seed, this can then oxidate the germination inhibitors. This shift in hormonal balance then allows the seed to begin germination.
However, we can eliminate need for stratification by soaking the seed in Gibberellic acid (GA). GA is a form of gibberellin, common growth hormones found in all plants. This is absorbed through the seed’s membranes and alters the hormonal balance similar to cold stratification, effectively eliminating 3 months of dormancy. This simplifies the process, in reality there are more factions that come into play in order to break dormancy, but it illustrates how useful GA can be in common applications.
There are a wide range of methods to applying GA to the seed, as well as varying concentrations and exposure times. For this treatment, a long soak time of 24 hours was used to allow the seeds plenty of time to become fully imbibed. With a long soak time, a small dose of just 200ppm of GA is required. This also reduces the chances of negative effects such as leggy seedlings that can come with applying growth hormones externally. After soaking, the seeds are cleaned with tap water to remove excess GA, further preventing side effects after germination. The seed is then sown as normal.
GA can also be used in conjunction with cold stratification. This is useful on seeds that are particularly difficult to germinate, such as Pinus. Before sowing the seeds, they are subjected to both a three month cold stratification and a GA treatment. This further increases the chances of tipping the internal hormonal balance and having successful germination.
This article is more advanced stage performed before the propagation methodology discussed in my further post . I recommend further reading before trying it yourself as this short piece is far from comprehensive. It will probably take some trial and error, maybe don’t do all your seed at once, particularly if it’s precious. When handling Gibberellic acid always wear gloves and treat chemical waste responsibly, don’t pour it down the sink!