1.1 Container:

To ensure that the root system of the trees produced have no imperfections that would be detrimental to their long term health and structural survival, it is proposed to use the RocketPot S1020 1.5lt Air Root Pruning, reusable, flat packable, container for the production of direct sown trees.

The S1020 comes as a flat injection moulded panel that is folded and self-locks to form a container. The sides and bottom of the container are cuspated with a total open area of 20%. The S1020 is made from high impact HDPE with high UV stability and will have a useful working life of 10 cycles or more.

1.2 Potting Mix:

The potting mix is produced from a range of materials; organic, inorganic or a combination of these. The mix must produce a desirable matrix of particles that can support the root system of the plant structurally and hold moisture and nutrients available for the plant to absorb.

The Potting mix should be substantially stable and not decompose or shrink excessively during the production cycle.

The basic mixture should have a known available nutrient status that is supplemented as required to meet the demands of the plant for the desired time period. The pH of the mix should be adjusted to meet the preferred pH of the species being grown. The higher the organic matter in the mix the lower the acceptable pH can be to match the plants preferred nutrient profile.

A typical Potting mix is listed in Appendix I. However, trees grown under a contract can be tailored to closely match the pore size and soil type of the planting site. The mix is compacted after filling, leaving 25mm of clear space above its top surface.

1.3 Pre Sowing:

The filled pots should be fully hydrated – preferably by placing in a flood and drain bed with water reaching 75% up the side of the S1020 pot for between 12 & 24 hours.

1.4 Sowing Method:

Seeds are sown directly into the S1020 Rocketpots. This can be done by hand or using needles under vacuum to pick and place the seed. Multiple seeds are sown, anticipating the variable viability of seeds. The depth of sowing and the inclusion or exclusion of light is adjusted to meet the germination requirements of the species being sown. Many species require pre-treatment of seeds prior to sowing.

1.5 Post Sowing Hydration:

The pots are placed within a flood and drain bed system. Initially, water is applied as mist to the top surface of the S1020.

In most species roots will penetrate 180mm to the bottom of the S1020 pot by the time the first two true leaves have developed, and the plant is 10 – 20mm high.

In addition to misting, a flood application of water may be required before germination.

This will depend on some or all of the following; time of year, temperature, humidity and evapotranspiration and germination time. Where germination takes less than 14 days flood applications should not be required. Where germination is longer, flood and drain applications may be required. Care should be taken not to over water the plants.

1.6 Flood and Drain Method and Frequency:

Plants grow best when their root systems are taken from saturation down to near wilting point and then fully rehydrated. Thus, pore spaces are filled with water when flooded and oxygenation is maximised when the mix approaches the plant’s wilting point.

High organic potting mixes become hydrophobic as they dry down to these levels. The open nature of the mix can see water bypass pockets of dry soil. This can be prevented by flooding the S1020 pots to 90% of potting mix depth for at least an hour, thereby preventing dry pockets. Maintaining the flood for up to 24 hours to ensures that the organics fully rehydrate.

Flooding frequency is controlled by plant size, wind and weather. Weighing the pot and plant as it dries and comparing it with the weight at field capacity provides the best guide to watering frequency. Hand lifting a sample plant here and there soon demonstrates when the next flood sequence should commence.

1.7 Plant Selection:

Multiple seeds are sown with the aim of getting at least three plants to germinate in each pot. When these seedlings are between 20 – 30mm high the least desirable plants should be nipped off with scissors. Unwanted plants should not be pulled out, as this will damage the lateral roots of the remaining selected plant.

As the trees grow, now individually in S1020 pots, it is possible to utilise a Shigometer to determine the Vigour of each plant. Seed grown plants each have different genetic characteristics which is manifested in the width of the Cambial Layer.

A set of needle probes, connected to the Shigometer, is introduced through the bark of the seedling and readings are taken. Low resistance means a thick Cambial Layer – High Vigour, and High resistance means thin Cambial Layer – Low Vigour. By selecting a representative cross sectional sample of all the trees a range of readings can be collected.

These numbers are then totalled and divided by the number of samples, at least 20, to provide a mean. The mean is the average and thus all plants with a resistance below the Mean are classified as High Vigour plants and all plants with resistance reading above the mean are classifies as Low Vigour Plants.

Planting High vigour plants in poor sites is more likely to see the trees survive, whereas Low Vigour trees in poor sites will probably fail. Medium vigour will grow in Average sites.

In this way a more even stand can be established. This can be particularly important in avenue tree selection where a substantially even growth rate across the length of the avenue is desirable.

1.8 Pest and Disease Control:

Germinated plants are very sensitive to pests and vermin. Some plants like Hymenosporum flavum attract snails, while Eucalyptus leucoxylon attract moths. These pests seem to appear from nowhere, particularly at night. In the Autumn foliar pathogens also appear. These are a particular problem if the potting mix is retained at high moisture levels. An integrated pest management system is essential, coupled with good nursery hygiene.

1.9 Nutrients in the Potting Mix and Supplementation:

The fertiliser regime is tuned to ensure the best calliper to height ratio. The aim is to avoid lush high nitrogen dependent plants. Nutrient levels within the potting mix should be reduced one month before planting in the landscape. This will cause plant growth to stall.

The foliage takes on a yellow tinge. Nutrition should not be so low that the plants become unable to protect themselves from pathogens.

The type and quantity of fertiliser provided from seeding to planting out varies. It depends on production location and temperatures at different times of the year.

1.10 Training and Staking:

Plants should not be staked unless absolutely essential. Some trees germinate and spread over the surface of the pot. This is a competition response to gain space. Once this spreading has established a space footprint, either the trunk will lift up straight or the plant will send up a dominant shoot that will form a trunk. Many Mallee species form multiple trunks from a lignotuber. If staking is required for some reason, the stake should be flexible to encourage trunk calliper.

1.11 Size Specification:

Plant size at the time of planting out will depend on species and the natural conformation of the plant. For many Eucalypts, calliper measured at 10% of the height should be between 1.5 – 2% of the tree height. E.G. a 400mm tall Corymbia maculata should have a calliper of between 6 – 8mm.

Most planting will be undertaken when the trees are between 300 – 500mm. Such plants are wind stable with callipers of 6mm or more. In exposed sites, smaller plant heights, larger calliper and/or dense planting will help establishment without stakes. Where dense planting is used, thinning can achieve the required final planting density.

1.12 Establishment Rate:

S1020 planted at different times of the year, in different soil types and varying levels of available moisture will perform differently.

Growth to 4 times planting height within a 3 month period was achieved in typical February trial plantings of Eucalypts. The S1020 plants were hungry when potted on to 26lt or 50lt Air Root Pruning pots. Species were Corymbia maculata and citriodora, Eucalyptus camaldulensis and Angophora costata.

The 400mm S1020 hungry plants grew to an average of 1.6m within a 3 month period.

If the planting specification below is followed, this rate of establishment and height increment should be achieved or exceeded within most planting sites.