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

Disease 6 - Leaf twist virus in grapefruit

Citrus trees are best grown in warm to hot climates, with mild winters. Some varieties of citrus, however, can be successfully grown in colder climates, including this grapefruit variety, "Wheeney." 

The above photo shows a viral infection, with symptoms of yellow mottling on leaves and puckering, although this could be also due to a combination of frost and wind damage. Viral infections in citrus are untreatable and like with all other viral infections, prevention by buying specimens propagated from virus-tested and/or more resistant material is the key. 

Ref : Judy McMaugh, pg. 73-4

Disease 5 - Daphne Virus

Daphnes grow best in cool areas and need soils rich in organic matter and slightly acidic. They prefer semi-shade and a cool, moist root run, so mulching is important. Daphne odora, the most common species, suffers from a number of viruses. These viruses are untreatable, but more resistant varieties have been released, termed "High health" plants. 

Symptoms of viral illness are shown in the specimens above, found in the Royal Botanic Gardens. They can include yellow blotches, irregular streaks, dead flecks, twisting or puckering. Flowers are often small, distorted and green. The whole plant may be stunted. 

Ref : Judy McMaugh, pg. 107

Pest 8 - Borers in Cercidiphyllum

Borers are a major problem for ornamental trees. There are a wide variety of borers. Once infested, there is little that can be done to control the insects in the wood. Keeping trees as healthy as possible is the best way to prevent borer damage. Trees that are old, drought stressed, or over watered, or otherwise unthrifty are most likely to be successfully attacked by borers. Borers always attack at joins of branches. The activity of borers encourages fungal disease, general weakening and eventual destruction of that part of the tree. 

Most of the borers encountered are beetles but some are caterpillars of clearwinged or other moths and others are primitive wasps. Pictured below is the frass (collection of excreta, thread, dead material), which acts as a protective, cushioning covering over the hole of the borer insect. The plant affected is a Cercidiphyllum japonicum (Katsura Tree), a deciduous tree found in the Japanese garden area of the Royal Botanic Gardens. 

An attempt can be made to treat borers by applying methylated spirits via a straw down the hole and sealing the entrance with putty. 

On a neighbouring Katsura tree, there is also a preying mantis egg case or ootheca. 

ref : University of Idaho website, pers. comm. Marcus Ragus

Disorder 3 - Frost damage to capsicum

Frost and, more specifically, alternate freezing and thawing can destroy plant cell walls, often killing tender plants, but hardier species can be affected as well. Bedding plants and tender vegetables, such as potatoes and tomatoes, show a range of symptoms in cold weather: leaf darkening or yellowing, leaf curling, scorch, tissue destruction and even plant death. Here is an example of damage to foliage of a variety of capsicum following an early morning frost in the production gardens at TAFE. Preventing frost damage involves choosing planting positions carefully to avoid 'frost pockets' (where cold air settles at the bottom of a slope), or a position in early morning sun. Other tips to prevent frost damage : 

- don't apply nitrogen-rich fertilisers late in the season as they stimulate soft, sappy growth which is especially vulnerable to cold damage

- Cover plants with a double layer of horticultural fleece or in a frame when frosts are forecast.

- Grow frost sensitive plants near walls that may radiate some heat at night. 

Ref: Judy McMaugh, pg. 20, Royal Horticultural Society Website

Disorder 2 - Phosphorus deficiency in brassica seedlings

Phosphorus is one of three major elements required by plants for healthy growth, flowering and fruiting. It remains relatively immobile in soil and resists leaching from heavy rain or watering. Australian soils are often, however, deficient in phosphorus. 

In soils with low pH, phosphorus is less soluble and therefore less available to plants. This limits growth. Cold weather can cause a temporary deficiency. Symptoms include poor growth and leaves that turn blue-green but not yellow (as in nitrogen deficiency).  Oldest leaves are affected first. Here, in the brassica seedlings at TAFE, the leaves are a red-purple colour. 

This phosphorus deficiency can be corrected by planting out these seedlings in a soil with plenty of organic matter. Decomposted animal manure, particularly poultry droppings is rich in phosphorus. 

ref: Wikipedia and Gardening Australia, Judy McMaugh pg.10