Birch Bed Project

The Birch Bed at TAFE was an area we worked on from May 20th-25th. The main objective was to control for a large number of weeds that had populated the area. Existing plants included Betula pendula, Viburnum tinus/japonica, Wisteria sinensis, Hardenbergia violacea, Salvia officinale, Paeonia lactiflora, Rosa hybrids, Sysyrinchium spp., Buxus sempervirens.

OH&S issues :

Deep trough separating garden bed from lawn, in some areas a significant tripping hazard. Risk reduced by marking out area and making it visible to all.

Garden stakes a significant risk of injury, controlled by removing them prior to working in area.

Tools not used kept in one area and not left lying on the ground to control for tripping hazard and injury.

Identification of possible underground pipes or cables by noting site plan.

Barbed wire fencing marked out and made visible to all.

Careful weeding around roses because of the potential to be scraped or punctured by thorns.

General awareness of location of other people working around you.

Wearing usual P.P.E including steel cap boots, long sleeved shirt, trousers, gloves to protect against allergens, insects etc.

Most prolific weeds identified :

Black Nightshade (Solanum nigrum) :

Rope Twitch (Agropyron repens)

Chickweed (Stellaria media):

Shepherd's Purse (Capsella Bursa-pastoris):

Other weeds : Petty Spurge (Euphorbia peplus) :

White Clover (Trifolium Repens):

Scarlet Pimpernel (Anagallis arvensis)

Fumitory (Fumaria muralis):

The majority of weeds were seedlings, rosettes and young plants. Much of the Black Nightshade was baring fruit and flower. Shepherd's Purse was initially hard to identify - it has highly variable leaves at differing stages of its life cycle (early leaves oval, sometimes with scolloped or toothed margins; later developing deep lateral incisions cutting off a number of lobes in the middle of the leaf; sometimes no lobes at all; mature leaves extending towards base with a reduced petiole or sessile).

All these weeds are of concern in the health, vigor and management of a garden bed as they are serious competitors for nutrients and can limit growth of desired plants. Most are tolerant of a wide range of conditions, can rapidly establish themselves by growth of smothering rosettes, are prolific seeders and their seeds can lay dormant in the ground for a long time. In addition, many weeds can reproduce and regenerate vegetatively eg. Rope twitch, which spreads by underground rhizomes can also grow by stem fragments left behind after manual weeding.

Tactics for weed control are based on reducing number of weed propagules, removing or killing existing weeds, preventing and stopping weeds from forming viable propagules to avoid further multiplication and spread of actively growing weeds, and preventing viable weed propagules from moving to other areas.

Some examples :

Black Nightshade was removed by grubbing since it is has a relatively shallow root system and the amount of fruit and flower was an important concern in potential spread. Hand forks are probably the best tool to use for this, but garden forks can also be used to open the soil a little allowing manual pulling easier. This technique is time consuming and can be tedious, but is very effective for a small area, especially when working with numerous people. As much as possible, the fruits left behind were raked and collected. The waste material was collected and composted - temperatures in the TAFE open compost heaps can usually get high enough to kill viable seed (this is not the case in househould compost systems).

Rope Twitch is a little more labour intensive. It requires judicious and careful cultivation, usually with a garden fork to open the soil up a little to tease out the entire rhizome and root system. As mentioned before, any fragments left behind can easily grow again. A single leaf blade "flag" poking out from the soil can actually be growing from an underground system of up to a metre in length. Care must be taken not to invert the soil profile and this technique can also bring dormant weed seed to the surface allowing germination. The disposal of waste is also problematic too - heat from even large compost systems might not be enough to kill rhizomes. In this case, placing waste in plastic bags, sealed and exposed to the sun can be sufficient - a process known as solarisation.

Other techniques to prevent weeds from forming propagules include mowing or use of a whipper-snipper. This can greatly reduce the number of seeds set when weeds have flowers on tall stems and there is little time to control by other means. Usually repeated cuttings will be needed with this form of control, but it does buy some time.

Proper hygiene techniques after working on a job is extremely important in preventing spread of weed propagules and disease to other areas. Garden tools are cleaned in a proper wash down area, preferably where waste water can be recycled. At TAFE, we filled a wheel barrow with water and a small amount of biodegradable detergent to clean tools of contaminants.

Waste water and run-off is a major issue in nurseries for example. Collecting and recycling techniques now include the use of constructed wet-lands since they are a cost-effective and low-maintenance option for purifying waste water. They have the ability to reduce the nutrient load of run-off and have a high level of biological activity. This is particularly important for nurseries where significant levels of nutrients can leach from potting media during irrigation increasing the incidence of algal blooms in natural waterways.

Due to the large area infested with weeds, mulching with a layer of one part compost combined with two parts coarse bark nuggets and chopped sticks was used as a general control measure.

A metal rake was used to smooth the garden bed and achieve an even contour. This is important to do prior to mulching.

Initially, pH testing was performed on different areas of the garden bed using a colourimetric kit - results of 5.5 in some areas indicated the need for the addition of dolomite to raise pH (see soil assignment for further details on altering pH of soils). In addition to the dolomite, blood and bone was sprinkled over the beds, about a handful or 200g per square metre. Cardboard sheets were then layed down as a form of weed mat, which can block light to potential weed seed, inhibit emergence but also be able to provide essential oxygen and water permeability to the soil itself. Plastic weed matting is often problematic in this regard as it is generally impermeable and can cause anaerobic soil conditions, killing important soil microorganisms. The composted bark was laid over the cardboard at a depth of 6-8cm. Mulch has the other advantage of reducing evaporation from the soil surface by 70-80% (mulch creates a layer of still, humid air above the soil surface).

Finally, a neat garden edge was created by first marking out a line with conduit. Curves can be difficult to mark out, but stakes hammered in at selective points either side of the conduit helps. A square-headed spade is used to cut an edge at a 45 degree angle with its sharpened end at the edge line. A mattock can be used to help lift out the unwanted grass and smooth the edge. The angle helps to lock in the mulch.

Ref : CRC Weed Management Handbook, Gardening Down Under (Handreck)