Okay. From what I was reading about them I thought one of the advantages for nurseries to use them was they could be kept there all summer, bought and transplanted at any time.
That could be but there may be some limits. For example, how long does a bare root tree planted in the gravel bed have to stay there before the root system is developed enough for transplant? Second, are there zone limits. For example, in the north there may be limits because of the weather. Also, most nurseries are selling landscaping trees that have access to supplemental water when needed once planted by the homeowner.
Let's think of things conceptually. A rootmaker tree has a very dense fibrous root system. Even without any supplemental water, if I start a tree in an 18, transplant after 12-16 weeks to a 1 gal RB2, do a second transplant in late spring or early summer to a 3 gal RB2, I can plant the tree in the fall when it is still actively growing. However, we do get fairly reliable rain in the fall/winter. The root ball is completely undisturbed as the RB2 container unwraps from around the root ball which is set into the hole undisturbed. On the other hand, I've had poor results starting trees early and planting them directly from 18s in the spring. We get plenty of spring rain. Why, I just don't think the root ball is large enough coming out of an 18. I've had better success planting in the spring from 1 gal RB2s, but not as good as keeping them for the summer transplanted into 3 gals and planting them in the fall. I'm also in zone 7a where winter kill is not a big issue.
When a bare root tree is extracted, the tap root is usually cut and it has a weak root system. You have to plant these when dormant so the root ball has time to develop enough to support the top growth. This is one reason trees are often cut back. Bare root trees are said to sleep for a year, creep for a year, and finally leap in the third year. So, you are starting with a bare root tree. True that a gravel bed will improve that root system. Extraction from a gravel bed lets you more easily extract the entire root system rather than cutting roots with a shovel. However, the root ball is significantly disturbed when extracted. Yes, you can spread those roots out the best you can when you plant, but it will still take time for the roots to adapt to the new environment. I think you will get a better root system using the bed, but the tree will still have some challenges to overcome when transplanted compared to a rootmaker tree. The question is whether the advantage of the denser root system are enough to overcome the stress of planting when not dormant or to overcome the stress of the first winter in the north.
Thanks,
Jack
