Propagation of plants

In the Millenniun Seed Bank glasshouse RBG Kew

The gardens and woodlands staff either request seed and send it through the nursery to propagate, or request the nursery staff to collect cuttings or seed from plants currently within the gardens. There are a number of methods of propagation:

Seeds

Seeds are sown into a seed pan or plug tray. We use a mixture of 3 parts sieved peat-free compost to 1 part fine Cornish grit for most of our seeds (except those with specific requirements). If the seeds need covering we will then cover them with Cornish grit (if outside) or vermiculite (if in a glasshouse). The seeds are checked and watered on a regular basis.

Germination takes place either in our propagation house (which is kept at 15°C – 17°C), or in cold frames. We often sow directly into the ground, especially with native species.

Once the seeds have germinated and are showing their true leaves we prick them out into small pots containing medium-grade, peat-free compost, leaving them for a couple of weeks until established. The seedlings are then moved to cooler lighter conditions to grow on, therefore avoiding etoliation.

Cuttings

We collect cutting material around the gardens throughout the year. Cuttings are collected in the morning and put into a plastic bag with a splash of water. They are then brought into the nursery where they will be cut to the desired length and shape, and inserted into a seed pan pot containing 50% propagation bark and 50% Perlite, which is wetted beforehand. If there is a lot of cutting material it will be stored in the fridge throughout the day.

The cuttings are placed either in the propagation house, in outside raised beds or in deep pots, depending on the species and type of cutting.

Occasionally we undertake other propagation methods such as dividing, layering and grafting.

An example of a recent propagation is Dendroseris littoralis, the cabbage tree. This is the plant that Robinson Crusoe’s role model, Alexander Selkirk, supplemented his diet with (by eating the leaves) when he was marooned on the Juan Fernández Islands in the eighteenth century.

Seedlings in the MSB glasshouse RBG Kew

Propagation Protocol

Family:  Compositae

Genus:  Dendroseris

Species:  littoralis

Common name:  cabbage tree

Propagation method/s:   Seed, cuttings, air layering.

Seed:  Germinated in the Millennium Seed Bank at 16°C for 12 hrs of daylight and 12 hrs of night with 85% successful germination.

Cuttings:  We tried cutting one of these tall single stemmed trees into hardwood pieces averaging 35 cm long and sunk them into a gritty peat-free compost mix. They were fully rooted within 6 months. We also removed some of the top side shoots, these also rooted quickly and are growing nicely.

Air layering:  Currently being used at Kew to propagate from these plants.

Pre-treatments:  None required

Establishment:  Grown in peat-free, well-drained compost

Watering:  Keep well watered during growing season

Pests and diseases:   Powdery mildew, whitefly and red spider mite

Notes:

Air layering: the stem is wounded and then wrapped in a moisture-retaining substance such as Sphagnum moss, then surrounded in polyethylene film. This encourages the wounded region to grow roots. When sufficient roots have grown from the wound, the stem from the parent plant is removed and planted.

Pest control: Ideally we use biological control, (beneficial insects) which control the pests. We may introduce Encarsia formosa, a parasitic wasp which targets glasshouse whitefly. We may also use chemicals if the biological control is not working. We do two sets of clean-up sprays in late Autumn and early Spring to clean up any over-wintering pests and diseases, so that when we put our first set of biological control in, they have the best chance of beating the pests.