Seed Treatment, Sowing & Transplanting Suggestions
While seeds of a few native species will begin to germinate as soon as they are moistened, others require special treatments to overcome their innate dormancy. Unlike the vegetables and flowers that you may be used to growing from seed, our native seeds are essentially wild, unselected for rapid and synchronous germination, and often take several months to appear after sowing. In the wild, it is often to a plant's advantage to spread germination over a season, several seasons or even years, to help ensure survival of at least some offspring. The artificial methods detailed below help overcome natural dormancies that some seeds have. The seed treatments suggested for each species are based on our experience and that of Ribbonwood Nurseries, Dunedin, (www.ribbonwoodnurseries.co.nz) who have been growing a comprehensive range of New Zealand native plants since1978.
Sow Directly or Soak Overnight and Sow
Some seeds do not need special treatment for germination to occur; apart from very fine seed eg Hebe, Jovellana, soaking in water overnight before sowing will often accelerate the germination process. Then sow the seeds in trays or pots of a well drained seed mix, lightly covering them with the sieved mix or fine (2-3 mm) gravel chips. Place the seeds in a sheltered site and water as needed, to keep them evenly moist but not wet.
Stratifying seeds involves keeping them evenly moist in cold (or sometimes in warm) conditions, usually for several weeks. Seed sown in autumn and placed outdoors away from direct sun but where it receives day/night temperature variations, will often stratify naturally, and germinate in spring. If carried out artificially, the cold stratification temperature needs to be above freezing but no higher than 6°C. Small seed lots can often be stratified in the refrigerator eg sown in containers of moist seed raising mix that are sealed inside a plastic bag to retain moisture, and then placed in the refrigerator for the recommended period (usually between 3 and 10 weeks). After this the seed containers are put in a suitable place outside (a shadehouse is ideal) for germination and seedling growth, where they will receive warmth but will not dry out rapidly in direct sun during the day.
If you don't have room for seed trays or pots in your refrigerator, seed can also be mixed with peat or vermiculite (1 part seed to 4 parts vermiculite or peat), moistened uniformly, so that no water can be squeezed out of it (excess moisture can result in fungal damage to the seeds) and sealed inside a plastic bag or container for the required period. Moistening the vermiculite or peat with a fungicide solution can help prevent fungal damage to the seed. After stratification, the seed mix can be spread directly onto the seed raising medium, covered lightly if required, and placed outside.
Hard seeds such as those of kowhai, need to have their seed coats thinned so that water can gain entry to start germination. This can be done by rubbing the seeds on sand paper or making a small hole in the seed coat with a safety pin or a pair of nail clippers. Scarified seeds are then best left to soak a day before sowing. Very hot water that has just come off the boil, can also be used to scarify seeds: pour the water onto seeds in a cup, leave for a day, then sow.
Transplant seedlings when they have a few true leaves or are about 3 cm tall and can be handled easily. Transplant them gently into small (about 4 cm diameter) pots of a well drained mix that includes some organic fertiliser or incorporates mature compost, and water carefully, so they stay moist but not wet. When the roots have filled the pot (check the drainage holes for emerging roots), transplant again into a pot about 8 cm diameter. After the roots have emerged from the bottom of this pot the seedling should be a suitable size to plant in your garden.
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