Air Layering

Layering is a process which may occur naturally in plants, when growing stems root into the ground. This ability can be exploited in a technique to obtain a small number of new plants.

Air layering induces adventitious roots to form on a stem above ground - particularly useful for plants with an upright habit. Many plants can be propagated by this means. Below is an example on Schefflera arboricola (Dwarf Umbrella plant - a popular evergreen houseplant).

Here, the technique is shown on the Tasmanian native laurel, Anopterus glandulosus.

An appropriate straight length of current season's growth is selected and a sleeve is made with a plastic bag with the base cut out pulled down over the stem. A 1 - 2.5cm wide wound ring is made with a budding knife around the stem - this exposes the cambium layer which will respond hopefully by producing roots.

Rooting hormone applied can assist in this process.

Moistened coir fibre is then packed into the plastic sleeve to act as a rooting medium.

It is squeezed like a sausage and then each end of the sleeve is secured with appropriate wire or adhesive tape. The plastic sleeve is then covered in alfoil for insulation.

Opaque plastic bags are best because they retain moisture and reflect light, so the rooting medium does not become too hot. It also allows visibility of root production.

Most plants can respond in 2-3 months, but some stems can be slow to root and will need till the following spring. The rooted layer is removed by cutting through the stem at and angle just above a node on the parent plant. The new layer can then be potted in an appropriate potting mix.

Ref : RHS propagating plants, pg. 64

Raspberries - lifting, dividing and taking hardwood cuttings

Raspberries (Rubus idaeus) are cane fruits with rhizomatous growth that enables them to be divided. They flower and fruit on sideshoots of long, vigorous canes with a life expectancy of up to 10 years. Most flower and fruit on canes produced in the previous year, although there are some autumn-fruiting cultivars that fruit on canes grown in the same year. The cultivar in this activity was "Lloyd George."

Canes were lifted with a shovel and the surrounding weeds, in particular the rhizomatous agropyron repens (rope twitch), was carefully removed from clumps.

The rootballs of the canes were washed with luke warm water to reveal growth buds arising from their rhizomes.

Foliage was removed with secateurs since most of the canes were suffering from rust disease, which normally shows up as bright orange powdery pustules, but darken to black thick-walled spores as the weather gets colder. "Lloyd George" and "Neka" are particularly prone to serious infections. Control can be achieved by copper oxychloride or a sulphur based spray.

Canes of roughly pencil thickness were selected and prepared for hardwood cuttings. This was achieved by making a horizontal cut below a bud and a diagonal cut above a bud at approximately the same angle the bud is pointing and at roughly the distance of the width of the stem above the bud. The bottom of the cutting does not need to be scored like other hardwood cuttings (this normally helps to induce root formation).

Other thinner canes were potted to be planted out in a permaculture display. Dead canes that contained old buds and revealing dead wood when lightly scraped were pruned out.

The organic mix used for the cuttings and potted canes was made from the following recipe :

40L composted bark (sieved), 5L pasteurised sand, 3.5kg rockdust (dolerite, sieved), 500g BFA pellets (blended), 500g dolomite.

For hardwood cuttings, the mix is lightly tamped down and the base of the cuttings is dabbed in hardwood rooting hormone. An OH&S issue is to prevent this rooting hormone from coming in contact with skin. It should be promptly washed off if this happens.

Hardwood cuttings are lightly pushed into the mix about 1/3 of the way down. Several cuttings can be placed in the same pot. They were placed in the poly house after this.

Ref : RHS propagating plants, pc Marcus Ragus

Some more pests and disease around the botanic gardens

1. Leaf miner

There are a number of different insects whose larvae feed inside the leaves. They can be referred to as "leafminers." Adults may be beetles, wasps, sawflies, moths or flies. They lay their eggs on or in the leaf. Each species always produces the same shape and size "mine." Some look like blisters, some as in this case, look like meandering lines. A wide range of plants are attacked. Control is by removing affected leaves promptly.

2. Case moths (order Lepidoptera)

The larvae of these moths make bag-like structures to protect themselves while they feed on foliage. Different species will have different ways of covering these cases - some have no coverings at all. Below is an example of a case moth larvae which has covered its case with pieces of twig and leaf. It is very well camouflaged. The case increases in size as the larva grows. When fully fed, pupation occurs inside the case. Female moths are wingless and lay eggs inside the case. The larvae that emerge will disperse and make their own cases.

A wide range of plants are affected by different species of case moth. Control is by hand removal of the cases.

3. Leaf Spot - Iris x germanica

Below is an example of this disease which is caused by a fungus which attacks plants in their dormancy. It first shows up as tiny brown spots, each with a watersoaked area around it. As these spots enlarge they turn grey and develop brown to red margins. The spots eventually coalesce to form large dead areas and the leaves are killed. Ongoing spread can weaken plants and hinder flower production.

Worse in warm, wet weather. Fungal spores are spread about by the wind and by water splash. Irises grown from rhizomes commonly have this disease. Irises grown from bulbs are less affected.

Control is by removing affected foliage and destroying. In severe infections, a copper oxychloride spray can be used. A suitable wetting agent can help the spray stick better to leaf surface. It may be necessary to repeat treatment every 10-14 days in ongoing humid, wet weather.

4. White rust - Capsella bursa-pastoris

This fungal disease affects plants in the Brassicaceae family. It is not related to the group of disease generally referred to as rusts. Usually it is characterised by small raised yellowish-green spots on upper surface of leaves with corresponding white soft-looking spore masses on the undersurface. These spores are carried to other plants by the wind or by insects. Badly affected leaves are misshapen. It is most serious in cool, moist conditions.

Control of weeds is important - Capsella bursa-pastoris (shepherd's purse), Coronopus didymus (bittercress), Raphanus raphanistrum (wild radish) are part of the Brassicaceae family. Crop hygiene is important - crop rotation and destroying diseased plant material. Spraying is not effective.

Ref : What Garden Pest or Disease is That? Judy McMaugh

Preparing a site for planting in a larger scale production garden

During this practical session on April 30th, we worked in groups to prepare an area for autumn-winter planting of brassicas for the organic students at TAFE.

The soil in these areas are clay-based, (on feel somewhere between a sandy clay loam to a clay loam) and quite sodic.

Consequently, surfaces collapse easily during rain or irrigation, with the collapsed materials forming a dense surface crust. This impedes infiltration of water into the soil profile and inhibits emergence of seedlings. It can also influence drainage and removal of excess water from the profile as well as limiting the supply of oxygen to subsurface root systems and beneficial microorganisms.

The soil breaks into large clods which make for a very rough seedbed. Ideally, soil aggregates should be between 0.2 - 3mm in diameter.

Improving the structure of such a clay soil involves :

1. the addition of gypsum (Calcium sulphate) given that the soil is dispersive

2.addition of plenty of organic matter

3.judicious cultivation to break up hard and compacted ground (ie. only when soil conditions are right - not too wet and not too dry).

Dolomite (Calcium carbonate/Magnesium Carbonate) was added to raise pH of these areas.

In smaller garden beds, the double digging technique is a good way of mechanically relieving compaction, crusting in the top soil or hardpanning in the subsoil. For larger scale production areas such as the one in TAFE this is not necessarily practical. In this case, a rotary tiller and larger agricultural rotary tiller was used as shown below :

As always, there are benefits and disadvantages of using these machines.

Buried weed seed is brought up to the surface enabling them to germinate. Rotary tillers also can create a compacted layer at the base of the tilled soil. Aggregates in the tilled soil become pulverised. The organic matter that binds aggregates are exposed to attack by microbes. This is why repeated cultivation can steadily destroy a soil's structure. Mechanical tillage like this should only be done once and lightly - once a year probably at most, but with the maintenance of high levels of organic matter.

P.P.E. used during the operation of these machines includes eyewear, gloves, full sleeve shirt and long trousers, steel cap boots, ear muffs.

The smaller rotary tillers are propelled forward by the rotating tines and do not have powered wheels, although they may have small transport control wheels. An adjustable tine acts as a brake, slowing the forward moving machine due to friction as it passes through the deeper untilled soil. The operator can adjust the amount of friction/braking by raising and lowering the handlebars of the tiller. These machine can be pulled backwards or put in reverse to move over areas again, but care should be taken so that the operator does not stumble and pull the machine over himself. Both these machines had gear boxes to allow the forward speed to be adjusted whilst the rotation of the tines stays constant. The larger agricultural tiller has a dead man switch which when released stops the machine from moving forwards or in reverse. Unseen sub-surface objects, such as stones or buried garbage, are also potential hazards as they can abruptly and violently move in any direction.

The benefits of using these machines include efficiency and coverage of a large area, improving drainage and aeration which reduce potential for plant stress and the potential for pathogens.

Reference : Kevin Handreck, Gardening Down Under

Wikipedia - Rotary Tillers