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Germinating Japanese Maple Seeds

By Mark Fields


Older Japanese maples, 25 years or older, tend to produce a large quantity of seed.  The seeds of most varieties will ripen in the fall.  Keep a close eye on the tree as fall approaches to watch for ripeness.  The seeds are ripe when they are completely brown.  At that time you can easily remove them from the mother tree.   You can also wait until their leaves fall, the same times the seeds fall, and try to gather them up then.  Picking them from the tree is the preferred method since you won’t have to rifle through the leaves to get to the seeds in your lawn or mulch. 

After collecting them, the wing should be removed from each seed.  The seeds them selves have an extremely hard shell coating in order to protect them from the elements.  Under normal conditions, it would take two years for them to germinate naturally.  The first winter the hard shell will begin to soften due to the high moisture levels.  During the second winter, the shell will break open and the seeds will begin to germinate.  In most cases the seeds won’t even survive the two years required to germinate.  They will inevitably be mowed over, mulched over, killed with the weeds when spraying or eaten by animals. 

You have the option of shortening this cycle if desired.  After you pick the seeds and remove the wings, place them in a paper bag.  Then just store them in a cool dry place until early February.  The time of the year may vary.  Here in Indianapolis, I have found that the first part of February is the ideal time.  You will be sowing them after the danger of frost has passed.  This date is usually after May 10th here in Indy. 

Sometime during the first week or two in February, remove the seeds from the paper bag and place them in a bowl.  Add warm tap water to the bowl.  Be careful that it is hot to the touch but not boiling.  Fill the bowl with enough water that it will completely cover all of the seeds.  You will notice that most all of the seeds will float on top of the water.  Use a spoon to ensure that you get all of the seeds wet.  Most of them will remain floating.  Allow the seeds to remain in the bowl of water for around 24 hours.  At that time you will notice that most of the seed will have settled to the bottom.  The ones that remain floating are most likely not viable.

Pour the seeds through a strainer.  Place the seeds in a Zip-Lock bag with a moist, but not soaking wet, mixture of sand and peat.  I have used Metro Mix 570 or composted pine bark fines with good results as well.  Seal the bag and punch some holes in the bag with a bamboo skewer or a sharp pencil for some air circulation.  I usually spray a squirt or two of fungicide to prevent any molding.  Place the bag in the refrigerator until you are ready to sow them outdoors.

Prepare a planting bed in the ground or a planting tray.  In the ground I usually mix in some peat and sand with the existing soil.  Remove some of the mixture prior to sowing the seeds and after sowing, place about ½ inch of soil over them and water the area thoroughly.  In a tray I have had good luck using a sand and peat mixture or sifted pine bark fines.  Fill the tray with the mixture ensuring that you leave enough room to cover the seed with ½ inch of the mixture.  Water thoroughly and allow to slightly dry out between watering.  Watering too often will cause the seeds and the germinating seedlings to rot. 

In either case, keep shaded to prevent the sun from scorching the tender new growth.  You can place a suspended 50% shade cloth over the bed or tray to assist in this effort.  Japanese maples prefer a semi-shaded location. 

The seedlings will start to emerge in about 2 to 6 weeks.  It is best not to disturb them for at least a year, preferably two.  This will allow the root system to develop sufficiently to be safely transplanted.  It is also a good idea to wait until they are dormant to do this.  I have transplanted them while they are leafed after a year and a half and had fairly good luck.  I recommend that you wait until they are dormant. 

Using this method you will be able to produce a large number of quality seedlings.  If you don’t have the privilege of being able to collect your own seed, various quantities are available on eBay, Sheffield’s Seed or Misho Bonsai.

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