Container-grown plants
Once seeds have germinated, they must be moved into the light. For small quantities, a sunny windowsill, cool greenhouse, well-ventilated conservatory or cold frame is suitable. Take great care with watering, as each pot or cell must be watered separately, as there is no horizontal transfer of water between the cells. The outside cells dry out faster than the inner ones. Watering can be done from below, using a large tray or capillary matting, until the stage when the roots reach the bottom of the cell. Once they have reached that stage, the cells should be kept clear of the bench or ground, so that air pruning of the roots can take place. Watering from above will then be necessary. Apply liquid feed regularly until mid summer, if not using a slow release fertiliser.
Polytunnels, glasshouses and other indoor environments must be kept cool and well ventilated. Polytunnels should have mesh sides to above the height of the benching, to provide side ventilation, with ‘skirts’ that can be lowered in cooler weather. The temperature of the compost in the containers must not rise above 30˚C, nor go below 6˚C.
The following table gives the Horticultural Trades Association guidelines for the minimum cell volume, height and root collar diameter for broadleaves, at the time of supply for planting out.
Table 5a: guide to sizes of cell-grown broadleaves
| HEIGHT BAND (cm) | ||||
|---|---|---|---|---|
| 10-20 | 20-40 | 40-60 | 60-90 | |
| Min. cell volume (cc) | 50 | 100 | 150 | 200 |
| Min. root collar dia. (mm) | 4 | 4 | 6 | 8 |
Once plants have reached the desired size in mid to late summer they should be hardened off by moving them outside, or by lifting the sides of the polytunnel. lower nutrients, cooler nights and shortening days encourage the plants to stop growing and to form a terminal bud. Woody plants require a certain amount of chilling over winter, in order to respond to rises in temperature the following spring. leave the plants outside through the early autumn, but protect the roots from frost. The containers should be well watered before the onset of freezing weather. Either bring the containers into a frost-free building, or protect the roots by plunging the containers into straw, compost or similar. Cover the tops with fleece during frosty spells.
In outdoor beds
Seeds sown direct in outdoor beds need thinning or transplanting. Seedlings grown in trays or pots can also be planted out for growing on to a larger size. This process is described below under ‘Tree Nurseries’.
