Starting trees from seed is one of our favorite things, and we want to encourage you to give it a try, too! We're not sure why so many of us in the U.S. believe that they cannot grow interesting cultivars of Japanese Maples from seed (maybe it's just a really successful covert marketing campaign from US landscapers?!) The truth is that you can pick seeds from a red-leaf Japanese Maple and sow them, and the result will be healthy seedlings that can have a wide variety of leaf characteristics?
Sadly, the common misconception about our ability to start maples from seed leads most of us who want to grow red-leaf Japanese maples to a garden center or specialty nursery, to buy a grafted tree. And unlike the wide variation in leaf characteristics you can achieve from sowing seeds, in most cases the grafted tree has predictable foliage characteristics, and is attached to root stock that is more robust than some seedlings (often a normal green-leaf variety of A. palmatum). The graft union is an undesirable characteristic for a bonsai and it will normally always be visible - an obvious sign of human intervention. Even with mature bark there is normally some difference in the color or other characteristics of the bark, making it challenging to create a flawless bonsai.
Examples of Japanese Maple Bonsai Grown from Seed
We've found that when we sow seeds from Japanese maples, they will reproduce some approximation of the parent tree's characteristics. So, if you want a red-leaf maple bonsai and you sow 50 seeds from your favorite red-leaf Japanese maple, you'll end up with 25 with red leaves (the rest might be green or pink or something else!), and of those 25, ten might have a leaf characteristic that you like.
The tree in the image above is obviously a rough-bark variety - the leaves are medium size and the nodes are longer than many cultivars used in bonsai. You can see from this video that a seedling from this tree, only a few years on from germination, is already showing similar character in the bark:
Seedlings germinated from the unnamed cultivar below were a mix of lace-leaf red, full-lead red, and a green similar to the parent tree with large green leaves and colorful twigs, seeds, and petioles.
How to Sow Japanese Maple Seeds to Grow Bonsai
Pick fresh seed in early fall; you can judge whether it is ripe by how easily you can remove it from the mother tree. Fresh maple seed can readily germinate quickly without any special treatment. If you instead allow the seed to dry, then you may have to provide stratification. The simplest technique is to sow the fresh seed in fall in a tray of soil, keep the tray in a cold but not freezing place until spring and then set it out in the sun. Protect the young seedlings from late-winter/early-spring cold snaps and then watch them grow! Using a greenhouse, starting them indoors, or otherwise protecting them is a good idea.
Don't be afraid to experiment with plant genetics - just be prepared for surprises when you do, and embrace the natural variations!
(Footnote - the main image at the top of the article is actually fall foliage on a trident maple, not an Acer palmatum.)