Thank you for the information. My main problem is not having the room to overwinter a large number of trees so I was hoping to get them in the field in one season. From what I’ve learned, a fall planting isn’t ideal in my area so that’s why I thought I might have reasonable success going straight from the 18’s since they’d have protection and supplemental water. Considering that I’m just starting with radicals now, I’m not sure I’ll have time to step from 18’s to 1 gal and then get them planted all on the same season.
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Keep in mind that most of what you hear about planting time is for bare root trees, not root pruned trees. Here is the issue. A root pruned tree has a dense very efficient root system that has lots of root tips and thus can transport a lot more nutrients and water from a given area. However, the area contained in an 18 is tiny. So, when you plant from an 18, it has very little reach. If you plant the tree at home and watch over it daily watering when necessary, you can probably get a tree planted from an 18 to survive. It doesn't take much time to dry out the soil a couple inches deep which is the reach of an 18. There is a big jump in area from an 18 to a 1 gal RB2 and even a bigger jump to a 3 gal RB2. However, just planting from the larger container does little good, the roots need to have filled the container for the root ball to be that big and that takes time.
Here the last threat of frost is about mid April and I'm sure it is later in your area. Trees grown under lights need to be acclimated to the sun slowly and that takes some time. Even though the trees can go outside to filtered sun when the threat of frost is gone, they are going from a place where nights were relatively warm to a place where they are much colder. This can slow them down. Since trees in your area will go dormant before they do here, your growing season is shorter on both ends.
If you decided to go the indoor start with root pruning containers route, I would at least keep them in 1 gal RB2s for the summer and plant them in the fall. Unlike bare root trees that spend a season of sleep, then a season of creep, before they finally leap. When planting from an RB2, the root ball is completely intact and there is almost no gap in growth. I believe a larger root ball with a fall plant will give you better results by far than planting directly from an 18. You may want to split your trees into two groups and do both. Or, perhaps 3 groups and direct seed some in early spring as soon as the ground thaws.
By the way, I tried something similar with persimmons. I went for very high volume planting hundreds from 18s. The results were dismal. I've found that I've had to cut back my volume each year and plant across more years to get good results. I like to start with a lot of nuts, they are cheap. Some won't germinate. Some will germinate but die. Some won't die but just wont' be prolific growers. I cull keeping only the best trees when I go from 18s to 1 gal RB2s and cull a second time when I go to 3 gal RB2s.
Thanks,
Jack