Katsura seeds are “flying seeds”: they have little wings, exactly like maple tree or pine cone seeds. The pod dries up and bursts open, releasing the seeds. These tend to sprout as soon as they hit the ground, if conditions are right.
When to sow Katsura seeds
Katsura seeds are among those plants that have fully mature seeds when the pods are ripe, in autumn.
This means the germination rate is highest when the seed pod has just barely turned dry.
You can sow them immediately for best results.
Germination rates for fresh seeds is nearly 100%.
However, for areas with cold winters, it’s also possible to wait for spring.
Time your sowing so that seedlings may be transplanted to the ground in spring (with regular watering), after the first frost dates.
In the meantime, collect seeds from ripe Katsura tree pods and store them in a dark, dry place. Use a paper envelope so that they don’t mold as they dry out.
Germination time for katsura is 8 to 12 days. Let the plant grow for another 4 to 6 weeks before transplanting or thinning.
This means you should sow:
between February and April in the Northern Hemisphere
between August and October in the Southern Hemisphere
Sowing in the ground
It’s possible to start katsura trees from seeds sown in the ground directly.
How to sow katsura seeds in the ground
Collect seeds directly from the tree or recently fallen pods.
Keep them in a dry place until early winter.
When the first frosts have hit, mark a date about a month and a half later. That’s when you’ll plant them in the ground.
Plant under a thin layer of soil, just enough to cover the seed.
In spring, the seeds will sprout.
Why not let them fall and sprout naturally?
If you simply let them fall to the ground when the pods open up, many seeds will already sprout in fall. Since they’re too young, they’ll die because of freezing. Keeping them dry will make sure they make it to the “real” winter. They’ll remain dormant until warm spring weather sets in.
There is no need to “chill” the seeds, but for dormant seeds it helps break dormancy.
You can of course germinate katsura seeds in nursery pots.
Sowing katsura seeds in nursery pots
As described above, collect seeds and store them in a dry place if you don’t plan to sprout them immediately.
If you’ve a greenhouse where you can keep your seedlings out of the freezing cold in winter, you can go ahead and sow them immediately. They’ll sprout and grow (slowly) over the winter.
However, if you plan on growing the sprouts to transplant them as seedlings directly, best wait until the end of winter to germinate them.
Steps to start growing katsura from seed in pots
Collect seeds and store in a dry area (a paper envelope in a garage or pantry is fine).
Around two months before the last spring frosts in your area, remove the seeds from the envelope.
Soak them in water for 24 hours. This helps them replenish moisture. Floating seeds are empty and can be tossed out.
If you’ve only a few seeds and want them all to germinate, wrap the seeds in a moist cloth (but not wet), place them in a plastic container, jar, or sealed pouch in the refrigerator for one week. This bout of cold simulates winter and doubles germination rates. Stratification is the name for this technique. It’s optional though, especially if you’ve got seeds to spare.
Sow the seeds in pots, two or three to a pot, under just a quarter-inch (0.5 cm max) of soil (seedling potting mix).
Moisten the soil, and either put the pots in a germination tray or cover with clear plastic to retain moisture.
Place the pots in a luminous place but not in direct sunlight, which would dry the soil out too fast.
The seeds should sprout within 8 to 12 days.
When the seedlings have grown to two inches (5 cm), select the most vigorous one and cut the other two out (thinning).
As spring freezing must be over at this time, transplant to the garden. If needed, use a garden cloche during the first week to protect the seedling as it hardens.
Learn more about sowing Katsura
Katsura is one of the hardiest ornamental trees. It can cope with temperatures down to -25°F (-30°C). This is mostly due to the surprising germination strategy that the caramel tree (another name for the Katsura tree) has.
Indeed, seeds germinate early in fall, as the seeds touch the ground. Each seed is unique thanks to cross-pollination.
Many seedlings sprout immediately and only grow a few inches before winter cold hits.
Most of the seedlings die because of the cold. But a few particularly hardy ones survive.
These hardy ones will grow and bear seeds again when mature.
Their genetic material is thus heavily geared towards resisting the cold.
It’s a surprising way for a plant to develop hardiness. It “screens” its seedlings right after they sprouted! This is how the tree slowly crept uphill (in mountainous areas) and northwards.
Other plants have different techniques. They usually involve delaying germination until spring. This gives seedlings a fighting chance to settle in before the cold strikes.
In botanical terms, the fact of submitting seeds to the cold to unlock germination is called stratification.
It’s similar to chilling for fruit trees. Indeed, flower buds on trees must be exposed to the cold for the flowers to mature properly, as illustrated in this olive tree in cold weather page.
Smart tip about sowing katsura seeds
Keep a few seedlings to start training a katsura bonsai!
Image credits (edits Gaspard Lorthiois):
CC BY-SA 3.0: KENPEI
CC BY-SA 4.0: Salicyna
Steps to start growing katsura from seed in pots
