At the JBG nursery we have large amounts of stock and space is a premium. The main reason for this is that most plants we grow are cultivated from seed. There are two reasons for this: the difficulty of sourcing live material, and the desire to collect and maintain wild-provenance plants.
As I’ve discussed before, the garden maintains several foreign plant collections, but importing live plant material is risky in terms of increased exposure to new pests and diseases, and difficult (not to mention expensive) due to legislation. Seed is almost always easier, cheaper and safer to obtain from international sources. It is also a less destructive method of collection from the wild, since live plants do not have to be removed from their habitat (a practice at odds with the garden’s mission of conservation).
The second reason basically follows the first. A botanical garden is a living museum focused on research and conservation. Therefore, Wild-collected plants are of paramount importance and should be the bulk of collections. The best way to maintain genetic diversity in the garden’s collections is through seed.
However, germinating large amounts of seed stresses the nursery’s capacity; there’s always more seed to sow, and seedlings need to be pricked out and bumped up with frequency into bigger pots that need more space. Thus managing existing stock becomes inseparable from managing plants in production.
For example, we have around 600 Costus sp. currently in the glasshouse, and they are far too large for the pots. Sadly, we lack the space to pot them on when it’s really necessary. A way to combat this issue is to repot the plants back into the same size pot by girdling the roots; a technique applicable to most herbaceous plants with a fibrous root structure. I also find it useful in regenerating pot-bound nursery stock prior to planting, and generally view it as an opportunity to remove any root damage from pests such as vine weevils or root aphids.
It’s best to undertake this work when the plants have died back, and just before the growing season begins. Since Costus sp. don’t go fully dormant in the Jerusalem climate, the foliage must first be removed.
Next, the plants are removed from the pot, and the roots are teased out and cut back to fill no more than 1/3 of the pot.
Finally, the plant is repotted with fresh compost into the pot it was just removed from.
The cleaned stock is then watered and placed back in its position in the nursery. Iris BG, the garden’s stock database, is also updated to show the stock was repotted and cleaned. The hope is to plant these in the new tropical glasshouse in June, by which time the Costus sp. should have rooted through again.