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

Scarification trial

Many seeds such as acacias have very hard seed coats and require a physical method to allow water to enter the seed and break dormancy. Such a process is called scarification. This can sometimes be done with sandpaper, using nutcrackers or nicking with a knife depending on the type of seed. Soaking in hot (not boiling water) for up to 48 hours is another method. Seeds must be sewn directly after the soaking period and must not be allowed to dry otherwise they die.

This trial was to compare germination rates of Acacia verticillata and Dianella tasmanica when seeds had been scarified by soaking in hot water for 24 hours compared with seed that had been given no prior treatment.

10 seeds of treated and 10 seeds of non-treated A. verticillata were sewn in different punnets. The same was done for D. tasmanica. This occured on the 23rd April.

Photos of A. verticillata punnets taken on 19th May, about 4 weeks later, with top punnet containing treated seeds and bottom punnet non-treated :

After 6 weeks (non-scarified on left and scarified on right) :

Note the strike rate for scarified seed is 8 out of 10, whilst non-scarified is 2 out of 10.

This shows that germination rates are higher when Acacia verticillata has been scarified.

At 4 and 6 weeks no Dianella tasmanica had germinated, as is expected with the time it normally takes to germinate.

reference : RHS propagating plants pg 53-4

leaf bud cuttings

Most Camellias can be propagated from leaf bud cuttings of current season's growth that has begun to firm (ie. semi-ripe cuttings, where the base of the cutting is quite hard and the tip of the cutting is still actively growing and thus still quite soft). These cuttings include the leaf and axillary bud or node. This allows for many cuttings to be taken from the same stem. Cuttings are made the same size to allow ease of handling by ensuring most cuttings take root at roughly the same time. These are placed into the prop. mix after each cutting has been dabbed in rooting hormone gel, leaving the bud on the surface of the mix. Flower buds are pinched out. With bottom heat, rooting usually takes 6-12 weeks. 

We also took some leaf bud cuttings from a potted Ficus elastica cultivar. Using secateurs, a cut was made straight across a stem just above a node - a rule of thumb is about the distance of the width of the stem itself - and about 2.5cm below the same node. Keeping the waxy side of the leaf outermost, the leaf was rolled to form a cylinder, secured with a rubber band and placed into the prop. mix after a dab in semi-hardwood rooting hormone gel. The lead node should sit on the surface of the mix. The cutting can be supported with a small cane through the rolled leaf as shown above. This is kept in the misting house under humid conditons until rooted. 

Larger leaf Camellia varieties can be handled in a similar manner as shown below : 

Ref : RHS propagating plants, pg. 95, 120

Root Cuttings

A limited range of plants, particularly ones that naturally produce suckers from the roots can be propagated from root cuttings. In this activity, I propagated Wisteria sinensis, whilst others propagated Acanthus mollis, using this technique.

Appropriate cuttings were located by digging carefully with a trowel around the base of the selected Wisteria vine, ensuring no damage was done to the larger root system. Root cuttings were of pencil-thickness, although thinner root cuttings are also just as successful. The thinner the cutting the longer they should be. Cuttings are best done in autumn or winter when the plant is dormant. The cuttings are then lightly washed in water to remove soil.

Each root section is cut into approx. 5cm sections. To make sure the cuttings are inserted the right way up, the base is cut horizontally and the top at and angle.

The cutting is then dabbed in semi-hardwood rooting hormone and then inserted into the propagation mix.

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The cuttings are then watered thoroughly and placed into the misting house on top of a capillary sand bed with bottom heat.

Ref : RHS Propagating Plants, pg. 23-4, 158

Below is a photo of Acanthus mollis root cuttings prepared on 19th May and photographed on the heating and misting beds almost a month later on 17th June :

Cold moist stratification

Some tree seeds have a physiological dormancy which can be broken by certain levels of cold or heat. Such seeds need to be treated by stratification.

In this exercise, we used seeds from Betula pendula, Acer buegeranum, Zelkova serrata - all deciduous trees native to the Northern hemisphere. We chill seeds in a refrigerator at temperature between 0 - 5 degrees celsius, to mimic the passing of winter and to gain a more even germination. Seeds need to be kept moist and so are sealed in plastic bags before being placed in the refrigerator.

Betula pendula catkins were harvested from the TAFE garden.

Samaras from Acer and Zelkova spp. were collected from the Botanic Gardens.

The seed-raising mix used consisted of equal parts of pasteurised sand, cocopeat, perlite, combined with trichodry and mini-osmocote.

A low punnet was filled with this mix and tamped down gently but firmly.

Betula seeds were scattered as a thin layer across the mix and then covered lightly with the same mix.

Zelkova and Acer seeds were placed gently by hand in the mix and again covered lightly.

These were then watered and placed in plastic bags and refrigerated as previously mentioned.

Betula pendula stratification period was from 22/4/09 - 15/5/09 (25 days)

Zelkova serrata and Acer buergeranum from 22/4/09 - 14/6/09 (55 days)

After each stratification period, punnets were removed from fridge and placed on heating and misting beds.

Betula pendula seedlings all had excellent germination rates and were pricked out on 30/6/09 :

Ref :RHS propagating plants, pg. 54

Vegetative propagation of Lavandula stoechas

In this propagation activity, I took semi-hard wood cuttings from Spanish lavender bushes growing in the production area at TAFE. Summer to autumn is an ideal time to take semi-hard wood cuttings. 

Propagation material was collected from the field and taken back to the shed to be washed in a diluted 1% ammonia solution to reduce the chance of disease (Damping off is common fungal disease of seedlings if good hygiene practises when sowing have not been observed). Lavender did not need to be transported in wet newspaper. 

After filling and lightly firming a punnet with the propagation mix, I selected side shoot cuttings of about 10cm in length, being careful to cut horizontally at the base of the cutting below the nodal growth. Nodes are points of high growth activity and contain tissue that can readily differentiate into root growth for example depending on conditions. 

Each cutting was dabbed into a petri dish containing a gel rooting hormone. Once all cuttings had been treated in this way, they could be placed sequentially in the growing media starting from the back of the punnet and working in rows to the front. A dibbler was used to make a small space for the cutting to fit in such a way that it would not easily fall after being watered, but being mindful to not have leaves touching the growing media that would otherwise encourage fungal growth. 

The punnet was watered and then place in the misting house on a layer of sand. The misting system keeps cuttings cool and limits excess transpiration which is a major reason for propagation failure. Low punnets do have a higher water table but the sand layer they are placed on assists in drawing down excess moisture in the growing media by capillary action.

Hygiene practises observed : washing down table tops and cleaning secateurs with 1% methylated spirits, sterilising punnets, using pasteurised sand in propagation mix, using healthy, strong disease free material, washing cuttings in 1% bleach solution.

Pricking out lettuce seedlings

In this activity we used dibblers to gently lift individual lettuce seedlings from seed trays. It was important to handle seedlings by their cotyledons and not by the stem. Each individual seedling was placed in a propagation mix consisting of 50% compost, 50% pasteurised sand, 250gm of dolomite, 250gm of crushed biopellets per 50L of mixture.