Raising a plant from seed is one of the most satisfying aspects of gardening or growing plants. These brief notes will give you a few pointers to get you started.
Some species will require a bit of patience, but in general, it is not as difficult to raise good quality plants as might be imagined. Tuberous species, such as Arum and Arisaema, can be sown at any time of year although late winter or spring sowings are best. Germination can often occur with warming temperatures and the seedlings appear with the onset of longer days and higher light levels.
As a general rule, I use the following method for all tuberous Aroids (with the exception of tiny seeds such as Leucocasia gigantea):
Soak the seeds for 24 hours, changing the water 2 or 3 times. This allows the seed to absorb water and soften the outer seed coat as well as removing any remaining germination inhibitors naturally found in the berries.
Sow into a good quality compost mix. I use a 3 part ratio of multi-purpose compost, vermiculite and perlite. Fill pots nearly to the top, firm down, and lightly water. Then sow the seeds on top, before covering with around 1cm of your compost mix. Lightly water again.
Keep the pots just moist without letting them get water-logged or totally drying out. Germination can take a number of weeks depending on the species.
I never throw out a seed pot until after at least 2 years.
For tropical species such as Amorphophallus – I use the same compost mix, but usually add extra drainage in the form of perlite, or even sphagnum moss. Place pots in a heated propagator, or on a heat mat. Germination can be erratic. As long as the seeds remain firm, they will germinate in their own time.
With very fine seeds such as Colocasia, Leucocasia and Xanthosoma, surface sow onto moist and firmed compost. Water gently with a small watering can with a rose, or use a sprayer.
Much more detailed information on sowing Arisaema seed can be found on this website under the Cultivation Advice pages.
General seed sowing advice:
Use a good quality compost for your seeds. Do not allow seed packets to get damp before sowing (eg, by storing them in a shed or greenhouse etc), and ideally, store them in a fridge until sown.
Very small seeds can be surface sown, or covered with just the tiniest amount of fine sand or sieved compost. Water with a watering can with a rose, small watering, or use a sprayer.
As a general rule, most seeds can be sown at a depth of around 1 – 2 cm.
Some species require a period of colder temperatures before they germinate. If this is known to be the case, the description will specify this. In such cases, either sow late Autumn and place pots in a cold frame or somewhere similar, or place the pots in a fridge for around 4 -6 weeks. Germination will then occur in the spring with warmer temperatures, or when temperatures are increased in your growing environment.
Many plants will naturally germinate in the spring if they are sown in the Autumn, Winter, or early Spring.
A heated propagator or heat mat with gentle bottom heat can greatly increase germination percentages. Do keep an eye on pots drying out from the bottom if the heat source is from below as this is not always obvious when looking at the pots from above. Standing seed pots on capillary matting and watering the matting can help reduce pots drying out from below.
Some specialist plants such as Palms, Bananas and Cycads can require very high temperatures for germination – 30 degrees or sometimes a little more. I germinate all my palm seeds in ziplock bags of just-damp sphagnum moss at around 30 degrees. Seeds can be potted up once a root emerges.
Banana seeds can be notoriously difficult to germinate. In almost all cases, the seeds are viable, but they do require being tricked into growth. The seeds are hard, almost like small stones. Soak in water for 24 – 48 hours making sure to change the water 2 – 3 times. Then place them in sphagnum moss or pots and keep warm (30 degrees or more). A cycle of warm / cool can encourage them to sprout. An airing cupboard is ideal, or a propagator timed to come on and off overnight. Patience is required – germination can be erratic and between a few weeks to several months. Don’t throw ungerminated seed out!