What it means…?
Easy germinators: are species that germinate in 1-4 weeks when adequate moisture and temperatures of 20-21˚C are provided. These are mostly annuals or species from warm climates; only a few perennials fall in this category. In general, the seeds require a few months of dry storage before being sown in order to germinate well.
Most perennial and woody plants require some kind of treatment in order to germinate. These seeds are called dormant but this is just a natural protection or adaptation that prevents them from germinating in nature at an unfavorable time for seedling development.
Moist-cold stratification: this is a common requirement of many temperate species; in nature such seeds would germinate in the spring after passing through the winter cold. Artificially, these seeds will germinate after being exposed to about 3 months of cold and moist storage. This can be done by sowing and placing the pots outdoors or in the fridge (if you don’t live in a region with cold winters). The hobby gardener can also easily provide cold-moist stratification by placing the seeds in a Ziploc bag with moist vermiculite or, best for fine seeds, in between moist paper towel sheets (and inside a Ziploc). After the treatment, sow as usual or place the pots under light at 20-21˚C during the day and preferably a lower temperature at night.
For many species, a short period of cold-moist stratification (1 month) even if not absolutely necessary, will improve the uniformity of germination.
Warm-moist stratification: is needed by most temperate species that are flowering early in the spring and form their seeds by early summer (like Sanguinaria, Erythronium, Hepatica…). Some lilies also need first a warm-moist period to form a bulb; other species need it for the development of an immature embryo. Generally, these are species that if not sown fresh in the summer, they need to be kept moist at outdoor temperature until fall when they can be sown or transferred into cold storage.
Multiple cycles of warm-cold: are needed by species that have combined dormancy ‘problems’, which may include immature embryos, very hard seed coats, hypogeal germination, or most often, combinations of various types of dormancy.
Often you can get dizzy by reading particular recommendations for in and out of the fridge cycles.
Best for the hobby gardener that lives in a temperate region is to sow these species as soon as they are received, then place the pots in a safe spot outside, water regularly during the warm season, and… be patient. Some species will germinate in the first year, but there are cases when germination will occur in the second or even the third year. In the case of a few species, there are clear recommendations for the length of time needed for each warm-cold cycle, for others trials are still necessary.
Scarification: needs to be done for all the species with a hard seed coat to allow water imbibition. For example, it is necessary for all the legumes and it can be done easily for small batches by sandpapering the seeds for a few seconds; filing also works for larger seeds; nicking the seeds end is yet another variant.
Hot-water: works well for all hard coated seeds; it is done by pouring hot water over the batch of seeds, allow them to cool off, and then sow. You have to monitor very well the watering as these seeds will become very sensitive to desiccation.
Hydrogen peroxide: is easily available and can be used to soften the seed coats of some species, to allow a faster water imbibition.
Seed coat permeability and germination have been also increased by soaking the seeds in other substances like: sulphuric acid, ethanol, ether, citric acid, and so on. In some cases, combined treatments are necessary to overcome dormancy, for example stratification followed by scarification.
Gibberellic acid – the efficacy of GA3 on germination is well known but with many variants. It can replace or shorten the cold period needed by some species and improve the overall germination for others. Most commonly is used directly as powder. Personally, I never agreed with the much described method of adding powder GA3 to the seeds because it is impossible to provide a uniform treatment and it is hard to approximate the added quantity. But if some say it works, that is fine with me. Too much of the GA3 can alternatively have a detrimental effect either on the germination or later on the seedlings.
I use GA3 as a prepared solution (500 or 1000 ppm) and soak the seeds usually for a day in small cups (bought as paint-holders). For very fine seeds, I found that placing them in between a piece of water-moist folded paper towel and then pipetting a bit of GA3 solution on top works best (place the paper towel piece in a Ziploc). Next day, after you squeeze the paper towel, it’s easy to collect the seeds and sow them in pots.
Light sensitive germinators: it is best to include here all the species with very small or fine seeds that need to be sown superficially. There are though a few species with not that small seeds that are stimulated by light to germinate, like a few Pulsatillas, for example. These seeds are best sown indoors in pots, barely covered with a fine layer of the seeding mix, or just pressed into the substrate and carefully maintained at the right humidity. An easy method is to include the pots or whole flat in a bag until first signs of germination and then gradually open them.
There is also proof that application of certain wavelengths of light can break the dormancy of certain species.
Moist storage: quite a few species have what’s called hydrophilic seeds, which means they do not tolerate dry storage, at least not for long periods of time. So, they either have to be sown after collecting, or kept moist until sowing. This moist storage requirement is often coupled with other treatments.
There are many lists of species that requires moist storage but not everyone agrees 100% on them. We have tried to provide moist storage for the most commonly accepted species, which are actually quite a lot!