Conditions for maple seedlings
This year I wanted to try maples from seed, so I did quite a few. I'm not sure that they are growing like they should so maybe someone can tell me if I am doing something wrong. I did Amur, Japanese and Trident maples. All locally collected seed. Sewn outdoors for natural stratification. Once germinated they were pricked out into 4x4x5 pots in a mix of 5 parts potting soil to 5 parts pine bark to 1 part small clay granules (Pro's Choice, Turface). I figured this would be a good mix of aeration and moisture retention. I had been moving them in and out of the sun being cautious as I didn't want to burn a whole flat of trees. I now have them under shade structures that are about 50% at noon and less restrictive during other hours. I fertilize every 2 weeks with 10-10-10. The first Amurs are finally stepping up with multiple sets of leaves and growing trunks. Some of the Japanese maples are also gaining speed but there are many that are still at two sets of true leaves. The Tridents seemed to have just stopped and are sitting there. They may have been immature seed stock. I had very low germination on them.
So, do they need more sun? I built the structures as I figure these plants will not survive full sun in the summer. More N in the fertilizer? Should I be using something acidic as I have read maples like? I feel the soil mix and pot size should be fine. Definitely seen big seedlings grown in smaller pots (tubes). I can't complain too much for my first effort of the sort but I did hand transplant over 60 trees and I want the best success rate. They need as much size as possible to survive the winter. Let me know if you see anything glaring that I have missed. Winter suggestions also. I do not have a cold GH but the shade structures were built with wrapping plastic in mind so they won't be entirely "out in the cold."