The best way to multiply gardenia is cuttings, even though this technique isn’t always crowned with success.
Prepare cuttings at the beginning of spring. Stems shouldn’t yet be stiff or woody.
Select cuttings about 3 to 4 inches (8 to 10 cm) long.
Pinch off lower leaves, keeping only the topmost pair of leaves.
Dip the cutting in powdered rooting hormones.
Plant the cuttings in special cutting soil mix or in a blend of peat and river sand.
Place your cuttings in a well-lit place, without direct sun. Ensure air moisture levels stay high (you can cover the cuttings with a garden cloche or clear plastic to increase moisture levels).
Keep substrate a little moist.
Repot young plants when the cuttings have already formed nice leaves.
Marcotting gardenia
You can also try marcotting (also called air-layering). It’s similar to cuttings, except that the branch remains attached to the plant.
Basically, the goal is to wrap the branch with a clump of moist soil.
Roots will develop. Then, simply cut the branch off and plant it to a pot!
Scar bark along the branch with a blade (lengthwise, not round and round the branch). It’s ok to remove a sliver of bark and reveal the wood beneath.
Slip the whole branch through a plastic sheath that’s about 3 inches across and 6 inches long (15 cm). You can also simply use plastic food wrap or swaths of gauze.
Two inches (5 cm) below the mark, tie the pouch or plastic to the branch.
Fill it with a blend of soil-mix, sand and garden soil (a few handfuls of each). It shouldn’t be too clayish.
Extend the soil-filled space along the branch for a further 4 inches (10 cm).
Moisten the soil (wet but not soggy) and tie the top shut.
Every couple weeks, check the moisture and add water if necessary.
An easy way to do this is to have a small slit in the plastic.
You can stick your finger in it. If it feels dry, squirt water in with a hand spray (a syringe is easier).
Close the slit with tape.
Voilà! Your marcot is going to sprout roots in the area with the soil. This will take around 3 to 4 months at most. At this point, you can cut the branch from the mother plant at the bottom of the marcot and pot it up. Remember to keep the plant away from direct sun at the beginning, until roots develop more.
Again, ensure moisture in the air to make sure your marcotted branch survives.
Sowing gardenia from seed
Seed pods form on flowers if you haven’t deadheaded them. These are shaped like a wrinkly husk. The hull is rather thick and fibrous.
Break the husk up to reveal the seeds inside them.
It helps to soak the husks in water for 4-8 hours (overnight) to soften them up.
Once you’ve recovered the small seeds inside the husk, you can start sowing them in a blend of potting and garden soil.
Make sure it drains well enough so it won’t stay soggy
Add a couple spoonfuls of grated charcoal to prevent damping off.
Sow the seeds indoors early spring, in a tray. Cover with a light layer of soil. Keep at room temperature and mist often to keep the soil moist but not drenched.
After about 2-3 weeks the seeds will sprout.
Thin and keep the most vigorous ones once they’ve sprouted 2-4 leaves.
Transfer these to individual nursery pots.
Depending on the weather in your area, keep them indoors in their pots for their first winter, or transplant them to the ground in fall to let them develop roots.
The shrubs should bloom within 3-4 years. When growing from seed, expect slight variations from the mother plant because of cross-pollination.
Seed pods form on flowers if you haven’t deadheaded them. These are shaped like a wrinkly husk. The hull is rather thick and fibrous.
