Grow and care for kōwhai
IntroductionHow to grow kōwhai, get the best results for your planting and protect them from pests.
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Preparing your seeds for germination
- Drag each seed lightly across sandpaper about 6–7 times (hold the seed so the small dark depression is away from the sandpaper). This will scratch the surface enabling water to penetrate the seed and start the germination process. Take care not to scratch too deeply.
- Spring and summer are the best times to do this.
- Fill a six-cell plastic punnet with potting mix – or use a small yoghurt pottle or a seed-raising tray. Whatever container you use, ensure it has plenty of drainage holes in its base.
- Thoroughly water the potting mix and leave to drain.
- For each cell make a hole in the mix to a depth of about 1 cm (a nail is good for this).
- Place one seed into each hole and fill hole with potting mix.
Waiting for germination
- Put punnet in warm place out of direct sunlight.
- Water occasionally to ensure the potting mix does not dry out.
- Germination should be evident 2–4 weeks after sowing, depending on soil temperature and other factors.
Care after germination
- Once seedlings appear keep them in full sun.
- Do not over-water.
- Your new seedlings can stay in their punnet until they are about 8 cm tall and roots are beginning to come out the bottom of the pot.
- At this point it’s time to move them on to a larger pot on their own. A good sized pot at this stage is about 10 cm x 10 cm.
- Extract your seedling from their cell (push from the bottom) taking care to avoid damage to the roots. Try and ensure soil remains attached to the root plug that you remove.
- Partially fill the new larger pot with potting mix, place the seedling centrally in the pot and fill the remaining space with potting mix until level with the base of the seedling.
- Water the pot.
- Your seedlings will be happy in a pot this size for the rest of their first year.
- You’ll need to repot your plants into a larger pot (about 1.5 litre capacity) after their first year to ensure they have plenty of resources to get them to a size suitable for planting out in the wild.
- A suitable size for planting out might be reached after just two years but could take three years. Ensure some slow-release fertilizer is applied each spring.
Things to watch out for
- Protect your plants from slugs and snails (and rabbits too if they’re likely to be a problem in your area).
- Be careful when using herbicides in the garden.
- Kōwhai are particularly sensitive and easily damaged.
- Dependent on region and particular season. In Central Otago autumn planting, once some soil moisture is back, is preferred as it allows some root establishment before the summer moisture deficit hits. The actual month depends on rainfall and onset of winter, but is generally March/April/May.
- Stock must be very well hardened. Not just out of a shade house or from under a high water regime. Don’t store plants for too long before the job.
- Use longer-term controlled release fertiliser to aid plant establishment. Normal fertilisers can ‘burn’ roots.
- Size? Not too big. Again, this is species dependent, but a thick stem and good fibrous root ball is more important than height. Avoid tall specimens with skinny stems and long internodes.
- Choose a site with some soil!
- Think about the natural habitat of the particular species (e.g. wetter south slopes for Olearia hectorii, dry sunnier sites for kōwhai, slopes for kānuka to avoid frost damage).
- Soak pot in bucket of water before planting, as peat-based mixes can have dry spots in centre of root ball despite appearing wet on surface.
- Dig a hole broader and deeper than the container, scoring the sides if glazed.
- Try putting the soil on a sack to ensure the topsoil is not lost.
- Make sure there is plenty of loose soil beneath the root ball.
- Water the hole before planting if possible.
- The hole should be deep enough to leave a shallow depression after all roots are covered. The depression will direct rain and any watering to the roots.
- Ensure soil covers all roots. Exposure of roots will lead to drying-out of peat-based mix.
- Firm the soil around the plant but avoid heel-ramming which can cause roots to break off.
- Mulch with whatever is available… stones, dead tussocks, organic materials, commercially available mats.
- Animal repellents may be useful but don’t last forever. Tree guards help prevent rabbit and hare damage.
- In most soils fertiliser shouldn’t be needed, and may cause problems. It’s better to go back and fertilise the following spring.
- Go back and check on the plant’s health.
- Watering in the first summer will reduce losses.
- Weed control is most vital. Weeds are using precious water, nutrients and may be competing for light.
Although kōwhai are generally hardy and look after themselves as they mature, they must be protected as seedlings from animal and plant pests.
Kōwhai are palatable to a wide range of animals including farm stock and wild goats, deer, hares and rabbits. These animals must be prevented from gaining access to your new plantings.
A range of options exist to achieve that. The best and most cost-effective choice will depend on the size of the planting site and the animals that must be excluded. Stock and other large animals are best excluded from the entire planting site with traditional fencing.
Where hares and rabbits are the main concern, protection of individual plants is possible through the use of small rabbit-netting exclosures. These should encircle the plant leaving room for future growth and be at least 70 cm tall. For a large planting site it might be more cost-effective to rabbit fence the entire site rather than construct numerous individual exclosures. Whichever option is chosen, it is important that the rabbit netting is pegged to the ground to prevent the exclosure from being knocked over or rabbits getting underneath. Rabbit netting is available from farm and garden supply outlets.
Small plants of non-divaricating native trees and shrubs that you might want to plant in association with kōwhai can also be protected using commercially available tree protectors such as CombiGuard©.
Exotic weeds and grasses will compete with your planted kōwhai for water and nutrients. For best outcomes they need to be suppressed until your plants are large and vigorous enough to overtop the ground cover.
Spot spraying planting sites well before planting is helpful in providing an initial knock-back of weeds. This is only a temporary reprieve however, and it is common practice to back this up with follow-up spraying or more enduring methods such as weed suppression mat secured on the ground around the plant. Old carpet, squares cut from wool sacks, or commercially available weed suppression mats such as Ecowool© mulch mats can all be effective. Such mats also play an important role in helping conserve soil moisture.
Take particular care if herbicides are used to suppress weeds after your plants are in the ground. Kōwhai and other natives can easily be damaged or killed from careless use of herbicide sprays. Where appropriate, the use of grass selective herbicides such as Gallant © are better than generalist or broad-spectrum ones.