In order to ensure the best results when planting canna seed, gardeners should intentionally start their seeds’ germination, begin planting indoors, and closely monitor the germination temperature. Planting canna seeds is not usually as easy as planting canna bulbs or rhizomes, but good results can nonetheless be achieved with a bit of planning and care. In their native tropics and other warm areas, canna seeds will often grow wherever they happen to fall outside. Bloom schedule is often erratic under this method, however, and results are not always predictable. The best tips for planting canna seed relate first and foremost to intentionality.
Canna seeds are typically very tough, no matter what types of cannas are at issue. One of the first things that gardeners should do to encourage uniform germination is to chip or slightly nick each seed's dense outer coating. In nature, the outer shell will slowly soften over time in the moist soil. This is a protection mechanism for the plant, as the tender and sensitive sprout will only emerge once the seed has thoroughly burrowed itself beneath the soil, and only then once that soil has warmed enough to indicate the coming of spring. In an indoor environment, such protections are unnecessary.
Toenail clippers or the tip of a paring knife are usually the best options for canna seed nicking. It is important not to completely penetrate the casing, though. The goal is just to remove a small segment of the dark exterior, only as deep as the white seed lining. Any further and the plant may be too damaged to germinate. Proper nicking may take practice, but done properly can be an effective way to control canna seed sprout times.
Cannas tend to grow best in rich soil. Potting soil blends designed for tropical flowers are good choices, but any dense dirt — particularly that gleaned from a compost — will work well. Although it can be tempting to plant just one seed in each pot, gardeners are usually better served by grouping multiple seeds together, at least at first. Even with nicking, not every canna seed will sprout. It is usually best to plant more than are needed, just in case some fail.
Proper caring for cannas, particularly at first, requires that the soil be kept very moist — but not drenched. New seedlings also need a warm environment in order to break soil. A south-facing window ledge or sun room is optimal. One tried and true tip for encouraging heat retention is to tie each pot loosely in plastic, which creates an incubator effect. Sunlight will intensify and circulate within the bag, concentrating the heat.
Each canna seed should begin to show signs of sprouting within a week or two. Once the young plants have sprouted their first full set of leaves and their stem has protruded at least 2 inches (about 5 cm), gardeners should carefully transplant them to individual pots. The smaller the pot the better, as seedlings usually need tightly packed roots in order to thrive indoors. It is often necessary to transplant young seedlings two or three times indoors before planting in a garden or other outside location. Cannas intended to be potted or perennially indoors may require even more transplantings, stopping only once the flower has reached its full mature size.