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Useful tips from your nursery

April 30, 2010

Nurserymen producing seedlings or transplants of any kind want to send the best possible seedlings to the field. However, in practice, this is not always the case. If there is an oversupply of seedlings on the market, nurserymen will keep their seedlings for as long as possible so as to avoid having to throw them away, which would be costly.

Similarly, if there is an undersupply, seedlings will be sold too young so that nurserymen can keep up with market demand and keep their market share.

In the nurseryman's defence, this factor is often dictated by the farmer or the contractor who is planting the seedlings.

However, the onus still rests on the nurseryman to only release seedlings that are within the correct spec. This spec is referred to as a PQI or Plant Quality Index.

The guidelines for this index are as follows:

(These are average estimates and vary according to seedling tray size, locality, species and season. This guideline does not include clonally rooted cuttings.)

Age of seedlings

Determined when the seed was planted, and measured in months.

Pinus species

Winter planting: 5-7 months optimum. Summer planting: 4-6 months optimum.

Eucalyptus seedlings

Winter planting: 4-6 months optimum. Summer planting: 3-5 months optimum.

Wattle seedlings

Winter planting: 4-6 months optimum. Summer planting: 3-5 months optimum.

Plant health

Presence of disease and leaf color
All certified seedling nurseries should inspect plants for disease, insect damage, discolorations and general appearance prior to dispatch.

Plant size

Root collar diameter, height of seedling and general sturdiness of seedling.

The perfect size seedling should be double the height of the container it is grown in. If seedlings are too tall in relation to the container size, they transpire too quickly causing mortality.

Root plug status

Presence of white active roots, root spiraling. Presence of 'J' rooting.
Seedling root plugs should all show some new growth of white roots allowing transplants to recover and grow more vigorously in field.
Root spiralling occurs in seedling trays with round cells and causes seedlings to 'Bonsai' infield.
J rooting in Pinus seedlings can be caused from seedling thinning in the nursery. It will also give plants a long term Bonsai effect. This should not be confused with J rooting in field which is caused by the bending of the seedling plug in the hole.

Seedling trays

Currently in South Africa there are four seedling trays commonly used, namely the 128 shallow, 128 deep, 98 deep and plastic 128 unigrows with inserts. These are referred to as either 'deeps' or 'shallows'.

Shallow or small volume seedling trays produce a smaller seedling and are grown in a shorter time period in the nursery. They therefore cost less to grow and transport but have a higher mortality rate at transplant if not cared for correctly.

Deeps are preferred in-field as the seedling plug has a larger root mass and more growing medium to retain moisture under stress.

Growing medium

Currently in South Africa the predominant growing medium for timber seedlings is composted pine bark.

The last 10 years has seen a shift toward coco-peat or coir fiber being used at different percentages with pine bark. The benefits of this to the nurseryman and forester are tremendous.

Coco-peat is a stable growing medium that does not leach nutrients as much as pine bark.In-field seedling plugs retain moisture for longer, thus reducing planting stress.
Vermiculite and to a lesser extent Perlite are used in growing mediums.
To ensure your seedlings are up to standard:
- Work with your nurseryman and place seedling orders in advance, as it takes planning and timing to grow and deliver quality seedlings.
- Timber seedlings are NOT rain dependent. They continue growing in nurseries regardless of rain.
- If seedlings are required for poor sites, request they are grown in large volume trays.
- All certified seedling nurseries have access to PQI parameters. You may ask for them prior to receiving seedlings.
- Purchase seedlings from certified seedling nurseries, thus eliminating the risk of poor seedling quality.

Certified nurseries