Spring has come. Temperature is going up. We have had some wonderfully warm weather the last 3 weeks. Time to think about the seedling trays in my garden. I am aware that growing from seed take a long time. That will not stop me however, as I enjoy growing from seed way too much.
In winter I have sown a range of maple and elm seeds. These seeds were collected from trees growing along the street so I am not completely sure what species they are. Predominantly these are Japanese maples and possible some trident maples too. And a few random elm seeds I came across are in there. Time will tell I suppose. In any case, the first seeds started to sprout in late February, due to the warm winter weather we have had. Now with the sunny days they have shot up and started to produce their first real leaves. As they were very crowded I have started to thin them and repot some individuals. Often I repot seedlings in summer. But now it is possible too.
What do you need
I work with a few basic utensils. Mostly my fingers. Then I have a shallow tray of water, where I can put seedlings that I take out of the tray. Of course, a large flat container with substrate to plant the seedlings in. For substrate I use a mixture of good quality potting soil, enriched with some fertilizer and an equal amount of grainy substrate. All is sifted to avoid big lumps and create a fluffy substrate. The grainy component is there to facilitate later cleanup of the roots. I keep this substrate fairly dry before planting and I do water the pot at this stage. Finally, I use a chopstick or spatula to lift the seedlings.
How to transplant seedlings for bonsai
For starters, find a location out of the wind and in the shade to avoid unneeded stress for the seedlings. I start off by pushing the spatula vertically into the tray, a bit away from the seedlings. By subsequently leveling it the substrate with seedlings is lifted up. This will loosen the substrate and you can then gently (!) pull the seedlings out. Usually a bunch of them come up and I put all of them with their roots in the dish with water to keep the fragile roots wet. At this stage you usually have one long root going down and few side-roots. For bonsai we prefer horizontal roots for a good nebari. As the taproot has no function for us, I pinch the tip off between my nails, ensuring at least half of the total amount of roots is preserved. As we are at the start of the growing season and bursting with seedling energy this will only slow them down for a day or so.
For replanting I take the spatula. Holding the seedling with one hand next to the spatula, I push the substrate sideways with the spatula creating a small hole. At the same time I lower the seedling. The substrate being fluffy and dry it falls back into the hole directly covering the roots. Do this until you have filled the new container. I do NOT tap down the soil but let that happen naturally through watering afterwards. For this tray I kept a planting distance of 3*5cm so the seedlings can grow for the rest of the year in this container.
Aftercare for transplanted seedlings
Meddling with young seedlings and their roots make them somewhat sensitive to drying out. So once the tray is full, water the tray. I use a very fine spray, as regular watering can would disturb the substrate too much. Using a bonsai watering can or hose attachment that produces a fine mist is best. I then place the tray in the shade and out of the wind for 24 hours, after which the seedlings can cope with the normal weather again. Place the tray under similar conditions as the seedlings were before.
Do note: If you get your seedlings to grow strongly, think about baby-bending some seedlings to get tight movements.