How to Start Cannas From Seed. Cannas, with their huge banana-like leaves and flamboyant flowers, add a tropical look to any garden or patio. The easiest way to grow cannas is to purchase plants, but you can also start them from seed. Growing cannas from seed takes a little bit of time, but it is a simple and inexpensive way to grow a lot of plants. Here are some tips.
Start canna seeds indoors 10 weeks before your average last frost date in spring. Large, round canna seeds have a very hard seed coat and look like BB-shot. The key to starting cannas from seed is to remove a small bit of the seed coat (a process called scarification) so water can get inside the seed. To scarify your seeds, take a file and carefully rub off a small portion of the black seed coat, stopping as soon as the white underlayer appears.
Fill a plastic planting tray with seed starting mix and sow the seeds ¼ inch deep and about 3 inches apart in rows. The seeds will germinate faster if you place the tray on a special seedling heating mat, which heats up the soil inside the tray from the bottom up. The seedlings should germinate in about a week (if you don't use a heating mat it may take a bit longer).
Move the tray to a windowsill that gets bright, direct light for at least 6 hours a day as soon as the seeds germinate. Fertilize the canna seedlings with diluted liquid fish emulsion every 3 weeks. When the seedlings grow to about 4 to 6 inches tall, transplant each seedling into its own 4-inch pot filled with regular potting soil.
Keep the soil in the pots evenly moist. Transplant the cannas outside into the garden or into containers after the last frost. Cannas grow best in a site with full sun and rich, well-drained soil. For the best results, dig in an inch of compost and scratch in a little granulated organic fertilizer before planting.