If they are in 18s, the rule of thumb is 12 to 16 weeks. You then transplant into 1, 2, or 3 gal Rootbuilder II containers. I personally prefer to go from 18s to 1 gal and then to 3 gals. The specific time depends on the tree. When you use a well drained professional mix in you 18s, there are lots of voids and water runs right through the container out the bottom holes when you first plant them. As they grow, the air pruning causes upstream branching. As this continues, the roots fill the voids in the mix and it becomes hard to top water the 18s. You put a little water on top and it sits there for a bit before soaking in. You then add a little more and the same thing happens. You have to keep doing this until water finally begins dripping out of the bottom holes. It now takes a long time to water them. This means they are definitely ready to transplant. If you goal is to maximize growth, Dr. Whitcomb says it is better to transplant slightly early than late.
I generally remove the nuts when I transplant. This makes them less attractive to squirrels but they still want to dig in them and often bite them off. Squirrels are territorial so if you eliminate them from you area, it takes a year or so for more to move in. I use a box trap and forced conversion (baptism). Another approach is to build cages out of chicken wire stapled to some kind of frame. Keep in mind you need to slowly acclimate trees started under lights indoors to the sun. I start by putting mine on the lower deck which only gets an hour or two of direct morning sun and then filtered sun for the rest of the morning and shade in the afternoon. After several weeks I move them to my top deck that gets full sun all morning and shade in the afternoon. For sun loving trees, after a few weeks there, I move them to a spot in my yard that gets full sun. The rest I leave on that top deck. Cages let you move the trees as needed and keep them protected from squirrels.
I've considered a greenhouse but can't talk myself into it. You can't start trees in a green house in the winter because of the low angle and intensity of the winter sun. You still need artificial lighting in the winter. A heated greenhouse would let me start taking trees out a few weeks earlier but it isn't worth the cost, effort, and space to me. You should be able to find picture of guys setups with 2x4 frames and chicken wire. I don't bother with that. I do lose a few trees to squirrels each spring before I eliminate them but that is simply because I get lazy and don't start trapping them soon enough.
This thread shows my preferred transplanting for chestnuts:
http://www.habitat-talk.com/index.p...h-rootmakers-transfered-from-qdma-forum.5556/ It works well for my area and climate and for most trees I grow.
Thanks,
Jack
