If you want to produce soft seedlings, then there’s no issue. Just wait for the actively growing seedlings to reach the required size. To harden them, we have two choices. The best-known method is to withhold water gradually to stress the seedlings. This tells the plant to prepare for the worst and it will stop or slow growth, strengthen leaf cells and build up reserves in the leaves in anticipation of more favourable conditions.
This is the best way to harden. The plants will be able to withstand harsher conditions when transplanted, and develop vigorous roots and leaves with their energy reserves.But rain once the process has started will undo all your good work. For this system to work, one either needs rain cover or a reliably dry climate.The alternative is to withhold nitrogen from the plants. Nitrogen is the accelerator which governs plant vigour. When it runs short, the plants stop growing – this is the easiest factor for them to adjust. The plants can stay in this state for long periods and will remain so even with much rain or irrigation.
From the nursery
Nurseries aren’t factories and are usually subject to variable temperatures. This can influence when plants will be ready. But if climatic conditions prevent farmers from getting into their lands, the nursery can hold plants until required without loss. The age of the seedlings has very little detrimental effect, though their size and stage of development may be a problem.Lack of nitrogen keeps such seedlings from growing in the nursery – the problem is, they’ll have the same problem getting going properly in the land.
Nurseries should give these plants a whack of nitrogen before they are pulled or the farmer should water them with a handful of limestone ammonium nitrate (LAN) in a watering can per 2 000 seedlings. Otherwise, the roots (growing slowly because of the low nitrogen) will have to source nitrogen from the soil into which they’re transplanted. This causes a slow start and unevenness and I’ve often found seedlings that just kept alive without growing for weeks.
This dose of LAN in the seedling stage is good practice regardless of how the seedlings were hardened. It’s an immediate stimulus and the most cost-effective fertilisation you can do. It also ensures a uniform start, much more effectively than commercial mixtures for this purpose.Whether you grow or buy them, seedlings aren’t cheap. Many farmers consider transplanting a mundane chore, but it’s really a foundation which must be correctly laid. We can never make up for a poor stand, and the costs will be the same for a good stand with high yield potential, or a poor one with a low yield.
Bill Kerr (016 366 0616 or e-mail [email protected]).