Germination rates for katsura seeds and how to increase them

Updated on 22 September 2026Published on 22 December 2019

Four katsura seeds (Cercidiphyllum japonicum)

Dry, dormant katsura seed sprouts grudgingly: a quarter to two-fifths of it in ideal laboratory conditions, and often far less on a windowsill. Eight days wrapped in a cloth that is moist but never wet, tucked into the refrigerator, changes the arithmetic entirely, lifting germination to somewhere between 60 and 90% of the seeds sown.

The normal germination rate of dry, dormant katsura seeds usually is around 25 to 40%. This is for both Cercidiphyllum japonicum and Cercidiphyllum magnificum.

Read also:

Katsura seed germination rate

Plan on only having 10 or 20% that successfully germinate. Sometimes seeds are packaged together with non-viable seeds which can’t sprout.
If ever you have too many in one spot, simply thin them out. You can also transplant them to another location.

In laboratories, rates for dormant seeds hover around 40%. However, this is usually in conditions of perfect temperature and moisture. Actual rates in home settings are lower.

Ideal temperature for germination is 70 to 75°F (21 to 25°C).
Ideally, soil should be heavily moist but not actually wet.

Stratification, useful to increase katsura germination

You can double germination rates with stratification. This means to set the seeds in a damp, cold place for about a week.

How to stratify katsura seeds

For katsura seeds, an effective stratification is the following:

Wrap in a moist but not wet cloth or paper towel.
Set in the refrigerator (40°F or 4°C).
8 days is the recommended time.

Stratification nearly doubles germination rates. After stratification, from 60 to 90% of the seeds should germinate, as opposed to 40% without.

Three ways to treat katsura seed, and what each one yields

Katsura seed can be sown as it comes, chilled first, or kept under lights. The three routes are not equal, and the difference in the number of seedlings you end up with is considerable.

Three ways to treat katsura seed, and what each one yields
Treatment	How it’s done	Expected germination
None (dry, dormant seed)	Sown straight away at 70 to 75°F (21 to 25°C) in heavily moist soil	25 to 40% in the lab, often only 10 to 20% at home
Cold stratification	Wrapped in a moist cloth or paper towel, 8 days in the refrigerator at 40°F (4°C)	60 to 90%, nearly double the untreated rate
Light treatment	Spread on moist filter paper, three weeks at 15 hours of light a day, 75-80°F (23-25°C)	40 to 60%, sometimes no improvement at all

There’s no point in combining both stratification and light treatment: pick one, and stratification is the stronger of the two.

Exposure to light, influence on katsura germination

Exposing seeds to grow lights for most of the day also helps, but only for seeds that haven’t been stratified.

There’s no point in combining both stratification and light treatment.

Light treatment only increases germination rates from 40 to anywhere between 40 (no improvement) and 60%. It isn’t as effective as stratification.

Here’s how to submit seeds to light treatment

Spread the seeds on a tray on a piece of moist cloth or absorbent paper. Filter paper works well for this (as in coffee filters).

three weeks at 15 hours a day
at room temperature (75-80°F or around 23-25°C)
keep the cloth or paper moist but not soggy.

Cross-pollination, a possible culprit for low katsura germination rates

Increased germination rates for katsura — Chilling the seed first nearly doubles how many sprout

There are two katsura species: Cercidiphyllum japonicum and Cercidiphyllum magnificum. Cercidiphyllum is the name of the genus. Although not known to hybridize, their pollen is similar.

A female tree pollinated by a neighboring male tree of the other species may start forming seeds.
However, the fruit quickly aborts or the seeds are sterile. They won’t germinate.
Hybridization, a form of cross-pollination, hasn’t yet been discovered for these two species of the same family. It may occur in rare cases but none have yet been reported.

If a male Cercidiphyllum magnificum is growing not far from your female C. japonicum, or vice-versa, there’s a chance not many seeds will be viable and sprout.

Most probable causes for not having any katsura seeds at all

Katsura, a dioecious tree

Katsura is a dioecious plant. Each tree is either male OR female, but never both.

only the female tree can bear seed pods with seeds in them
but it needs a nearby male tree to pollinate the flowers and fertilize them

Male trees don’t bear fruit or seeds pods.

Female trees require male trees to bear fruit – they are not self-pollinating.

Any male of that species will do, as long as it’s really the same species (both C. japonicum or both C. magnificum). Within the species, any of the other katsura varieties will be compatible.

Why isn’t my katsura bearing seeds?

If your tree isn’t bearing seeds, it may be for the following causes:

it’s a male
it’s a female, but there isn’t any male nearby.

Lastly, your katsura tree may be too young. A tree must usually be several years old before the first flowers appear and it can propagate.

Read also:

Frequently Asked Questions

Why isn’t my katsura tree producing any seeds?

There are three usual explanations. Either the tree is a male, and male trees never bear fruit or seed pods; or it is a female with no male of the same species nearby to pollinate it; or it is simply still too young, since a katsura must be several years old before the first flowers appear.

Do you need both a male and a female katsura tree to get seeds?

Yes. Katsura is dioecious, meaning each tree is either male or female but never both, and females are not self-pollinating. Any male of the same species will do, and within the species any of the other katsura varieties will be compatible.

How do you stratify katsura seeds?

Wrap the seeds in a cloth or paper towel that is moist but not wet, then put the parcel in the refrigerator at about 40°F (4°C). Eight days is the recommended time. This simple cold, damp spell nearly doubles germination rates, taking them from around 40% to between 60 and 90%.

My katsura set seed but nothing germinated — why?

Check what else is growing nearby. The two species, Cercidiphyllum japonicum and Cercidiphyllum magnificum, have similar pollen, so a female of one species can be pollinated by a male of the other and start forming seeds. The fruit then quickly aborts or the seeds are sterile, and they simply won’t sprout.

Sources

Stratification and Light Improve Germination of Katsura Tree Seed, Michael S. Dosmann, Jeffery K. Iles, Mark P. Widrlechner, 1999, Iowa State University & US Department of Agriculture

Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Four katsura seeds by Józef Babij under © CC BY-SA 2.0
Katsura seedlings by Salicyna under © CC BY-SA 4.0

Written by Gaspard Lorthiois | Loves helping out, especially when it comes to growing things. Worked in herbal medicine, runs a farm, and dabbles in tech. Master's degree and engineer.

La page de Gaspard Lorthiois