Nursery stock are young garden plants (also called prebonsai), that sometimes have great qualities for Bonsai purposes. Buying Bonsai nursery stock is a fast way of ‘propagating’ a tree and you can start right away with training it.
Although it can be hard to find good material, it is an rather inexpensive and fast way to increase your Bonsai collection. One major drawback is that starting work on an older tree (instead of growing it right from the start) often means you will have to remove large branches, with visible wounds as a result.
Where to find preBonsai / nursery stock
Good quality nursery stock can be hard to find, try looking at small family owned nurseries (large commercial stores often don't sell rough material). Some (online) Bonsai shops sell nursery stock as well, but this comes at a price higher than at small nurseries. Check this article for a store near you; Bonsai trees for sale.
Nursery stock can be bought throughout the year, but most material is offered from early spring till late summer.
What to look for in nursery stock?
This is rather hard to explain, your skills to find potential material will improve once you learn more about growing Bonsai. However, key aspects to look for are the species of Bonsai tree, shape of the trunk, tapering of the trunk, the tree’s branching structure and its Nebari (root flare or surface roots). The photos below show examples of good quality preBonsai, very suitable to be trained as a Bonsai.
Young prebonsai material (Chamaecyparis), around $10.
Young Picea nursery stock, around $10.
Place the newly bought nursery stock outside (unless it is an indoor tree obviously) and keep it damp, but not wet. The trees can be fertilized using normal quantities as described in the fertilizing section. It depends on the season in which you buy the nursery stock whether or not you can start training the tree right away. When bought during the early spring you can prune and repot trees immediately, but if you buy trees later in the year you should wait until the next spring.
For reference material about training nursery stock check the Bonsai progressions part of this website. Or read the Bonsai training pages for background information about techniques like pruning, wiring etc. An excellent way to get a taste of this hobby, is to buy a Bonsai starterkit, and grow a Bonsai yourself!