Seed germination by definition is “the sum of events that begin with hydration of the seed and culminate in emergence of the embryonic axis (seedling) from the seed coat”.

In respect to our native flora, seed germination can take quite some time to achieve which is where a lot of people tend to either fail or give up.

When attempting to germinate any sort of seed, we need to bare in mind that much like people seeds all desire to grow big & strong we just need to provide them with the correct environment to do so.

1. VIABILITY

Seed viability refers to the ability of the seed to germinate. Potential viability may be ascertained by performing a cut test on a sample of seed. Healthy seed kernels when cut cleanly with a sharp knife should show a firm moist clear or white structure.

2. WATER

The ideal germinating moisture content of the soil varies from species to species. For most seed it is important that the soil is not excessively wet as this prevents aeration and promotes disease, or excessively dry that the germinating seed will wilt. Somewhere in the middle is sufficient to promote germination of most seed.

3. TEMPERATURE

Seeds require warmth to germinate. The ideal temperature for germination varies from species to species, temperatures between 15 and 25 degrees C will produce good results with most species. Hot pads or soil warming cables may be used to induce germination over winter or in colder areas. When using heating devices, it should be noted that an alternating temperature is usually more favourable than a constant temperature to induce germination. Another technique we use is simply placing our seed raising containers into a ziplock bag to create a warmer microclimate.

4. OXYGEN

Seeds require oxygen for germination to take place. Most seeds will not germinate when the germination medium is too wet, when the seeds are planted too deep, or when other conditions limit the supply of oxygen.

5. LIGHT

For most seeds light is not required to promote germination, however it is required to produce good stocky seedlings and must be supplied during early seedling growth. For this reason and because it does influence germination of some seed, germination should take place in good light, avoid direct sun light as this may overheat or burn the emerging seedlings.

Commonly a 2-stage approach is used to raising seedlings. Firstly, a quantity of seed is sown and germinated in a seed tray. From there individual seedlings are transplanted into separate containers for growing on to the planting out stage. This method works well for most species and has several advantages over direct sowing in open beds. The main advantage being that we can provide precise environmental control during the critical stages of germination and early seedling development.

Germination trays are recommended to be at least 50mm deep and provide good drainage. We find ice cream containers a really good size for use as germination trays, providing they are throughly clean and have ample drainage holes poked in the bottom.

For best results use a seed raising mix as seed raising mix is sterile. Composts & potting mix’s contain microbes, but these can be eliminated by treating your soil with boiling hot water than left to cool (back to room temperature) in a sterile environment such as a clean plastic bag.

Damping off is the main problem that may be encountered during the germination process and in early seedling development. It is caused by fungi attacking the seed before or shortly after emergence. The symptoms of damping off are failure of the seedling to emerge, or the death of the seedling shortly after emerging coursed by rotting of the stem at soil level.

The control of damping off disease can be tackled in two ways. Firstly, try to avoid environmental factors that encourage the growth of fungi in or on the soil, these are warmth (temperatures of 21 to 29 degrees C are the most favourable to damping-of fungi) waterlogged soil and prolonged damp conditions. They can be reduced by the use of good free draining soil mix & plenty of ventilation.

Almost any container can be used for growing on seedlings from old milk bottles to specially designed planters. Root trainers are suitable for small- or large-scale seedling production. They are designed to provide seedlings with a perfect container environment which promotes optimum root formation. They are easy to fill and hold a minimal amount of potting mix. They are available in a variety of sizes to suit most species of trees and shrubs and can be re-used. The design of the groves and shape of the root trainers guide roots straight down preventing root spiralling or binding. Roots are then 'air-pruned when they reach the drainage hole at the bottom. Their hinged book design can be opened to inspect root development, soil condition etc at any stage of development without damage to the seedling. This feature also allows easy removal of the seedlings when they are ready for planting out. Because all roots are intact then survival rates are high.

The recipes for potting mixes are many and varied. Most contain differing amounts of some or all of the following, washed coarse river sand, ground bark, decomposed saw dust (untreated) peat, and a mixture of fertilisers and trace elements.

The following is one recipe that has been used successfully.

1/3 peat, 1/3 decomposed sawdust or ground bark and 1/3 coarse river sand. Added to this is a slow release NPK fertiliser at 3-4 Kg per cubic meter, dolomite at 3-5 kg per cubic meter, super phosphate at 1-2 kg per cubic meter and a trace element compound.

Whatever recipe you use it must be free draining for good aeration yet have good water holding capacity and supply the necessary nutrients for healthy seedling development. If you are not into making your own, then most garden centres or landscape suppliers sell ready-made potting mix.

Fill a seed tray with germinating mix, firm down and water well. Sprinkle the seed evenly over the surface. Cover with a fine layer of mix no greater than 1-2 times the diameter of the seed. At this stage trays should be placed in a warm well-ventilated shady spot and watered regularly until germination is complete. Avoid over watering as this can create conditions which favour fungal disease. If young seedlings become spindly during early development, they may require more light.

When seedlings are 2-5cm high or big enough to handle they should be pricked out and transplanted into their individual containers. At this stage it is good practice to cull out any seedlings that don't look strong healthy and vigorous. Pre-fill containers with moist potting mix and using a thin stick make a hole in the centre of the container deep enough to accommodate the roots. Very long straggly or distorted roots should be cut off. Lower the seedling into the hole so that the uppermost roots are a few millimetres below the surface, taking care that the roots are not folded or turned upwards firm the soil around them using the stick. To prevent damage the seedlings should be handled with care by their outer leaves not there stems or growing tips. Care should be taken not to allow their roots to dry out. After transplanting, seedlings should be watered and placed in a shaded area to be hardened off before they are moved to where they are to be grown on to the planting out stage.