Protecting Plants against Bad Environments

Horticulturists have Many Ways of Protecting Plants from Negative Environmental Conditions

Environmental conditions can vary considerably even from one part of a property to another. You must choose the appropriate plants for the conditions you can offer it; or alter the conditions offered to suit the plants you grow. Plants are normally most sensitive to environmental problems when they are young, so it is important to:

• Acclimatize a plant to its new environment before removing it from the pot and planting it into its new position.
• Plant at a time of year when severe environmental problems are least likely (eg. flood, heat waves, snow, frosts, severe storms -avoid planting in these seasons)
• Provide protection to young plants to ease them into their new environments:

PROTECTIVE STRUCTURES

Greenhouses, shadehouses, cold frames and cloches are structures used to protect plants from undesirable environments and provide better conditions for growing.

A GREENHOUSE is a building with a roof (and often sides) made from glass, plastic or some other material which will allow light and warmth to enter during the day, but insulate against cold temperatures during the night.

A SHADEHOUSE is a part or fully enclosed structure with a roof (and sometimes sides) made from a material which filters light entering the area, to provide more suitable (lower) light intensities for plants growing there.

The main reason to use a greenhouse, shadehouse or some similar structure is to provide a better environment for your plants. In some circumstances these structures can also be very useful as a cover for swimming pools or spas.

GREENHOUSES do the following...

• Create and maintain a higher temperature than the outside environment. ‑Protect plants from frost.
• Create a more humid environment than the outside in drier areas.
• Create an environment with a different balance of gasses to that found in the fresh air outside.
• Provide some degree of protection from wind, hail and pests.

SHADEHOUSES do the following.....

• Create a darker environment suitable for plants which prefer lower light intensities.
• Remove the danger of sunburn for sensitive plants.
• Protect from frosts.
• Provide a shady, protected environment for human use.

Cold Frames

This is an enclosed structure with a lift up or lift off roof. It is essentially a small glasshouse, performing a similar job to a glasshouse ‑but you cannot walk inside. They can be useful for raising seeds and cuttings.The frame is a simple structure, with wooden or polyflute sides and a hinged glass top, usually about a metre high. The top is at an angle (so water can run off, and the sun enters at nearly right angle) and can be opened and closed for access and to allow air in, depending on the weather. Opening and closing the lid controls the temperature and humidity. The advantage over a glasshouse is that you get more space for fewer materials. They can be moved around to find the best spot, or changed from a sunny position to shade depending on the season. They can be designed so that new frames can be attached to previously built frames. The disadvantages are that you are working at ground height and not at a bench, and because of the smaller internal volume, the frame can heat up and cool down faster, and so it needs to be watched more closely. The angle of the top faces nearly at right angles to the sun, in an easterly or northerly direction. The back wall faces west or south.

Cloches

These are like mini, moveable greenhouses which can be placed over tender young plants, particularly in cooler climates, to help protect from cold nights and generate warmer conditions during the day. They are typically used on seedling vegetables in late winter or early spring, to protect from environmental damage, and allow plants to get established faster.

All too often, however,people put plants in such a structure just because they have the structure, when the plants might just have been better off left outside.

Remember:

• Some varieties of plants prefer cooler temperatures than you will find in greenhouses.
• Most plants which prefer a greenhouse environment will benefit from a spell outside for at least part of the year.
• Plants which prefer a shadehouse in the intense summer sun may require a better lit position over winter.

Staking Plants

Plants are staked for the following reasons:

1. To support weakness in plant tissue until it strengthens (ie: if wood is soft & liable to break, the stake supports it till it gains strength).

2. To reduce likelihood of damage through movement ‑wind may break the plant at the base.

3. To reduce likelihood of physical damage through vandalism, mowing, cultivation etc....by actually placing a physical barrier to prevent disturbance to the plant. HINT: If stakes are removed by vandals...try smearing grease on the stakes to deter them.

4. To support transplanted plants (where the root system was cut back), until the roots can regrow and establish a firm hold in new ground.

5. To mark the location of small plants (ie: tubestock), so it is not inadvertently damaged by mowing, cultivation, etc.

The main dangers with staking are:

• Leaving ties on a plant too long....the stem grows, and the tie cuts into the bark, ringbarking the plant.
• Tying too tightly to the stake.... if the plant does not move in the wind, the root system/trunk may not develop adequate strength to support the plant when the stake is removed.

Tree Guards

Tree guards are used for three main reasons:

• As protection against differing climatic conditions such as frost or strong winds
• As protection against grazing animals such as rabbits, sheep, goats or cattle.
• As a barrier to prevent damage by machinery, for example mowers.

Types of Tree Guards

• Plastic Tubes - The most durable types are UV stabilised ‑ these should last for several years. In many cases, plant growth is significantly enhanced as the tubes create a warm, moist micro‑climate. Protection from frost, wind, and rabbits is normally excellent. Requires 3‑4 stakes to keep the tube upright. Plastic shopping bags, old fertilizer bags etc. can also be used as a cheaper alternative, although they will not be as long‑lasting or effective.
• Plastic Mesh  - Durable guards which are available in both flexible and rigid forms. These require pegs or stakes for support.
• Plastic pipe - Flexible plastic pipe, 50‑100 mm diameter x 500 mm length, can be placed around stems of young frost‑sensitive plants (eg.fruit trees). These should be removed after the danger of frost has passed (fungal problems may occur, as the pipe tends to keep the stem damp).
• Wire Mesh - Chicken wire tied to stakes or stapled to 3‑4 pegs provides a barrier against grazing animals. Fairly cheap and long‑lasting.
• Hessian - Hessian bags or cloth need to be tied around 3-4 stakes. These provide good wind and sun protection although they often tend to sag over time, and should last 2‑3 years.
• Tyres - Old car tyres placed around seedlings can be an effective and cheap barrier against rabbits and hares.
• Milk cartons - Useful for marking location of seedlings and providing limited protection against vermin, frost, etc. Will last for 1‑2 years.

What should you look for when you're selecting a tree guard?

1) Do you really need it? Most plants are better off without them, establing in the conditions under which they'll continue to grow.

2) Select a tree guard which will best suit your needs. You may need to consider more then one problem, for example, frosts and protection from cattle.

3) Cost - can you use recycled materials, or will you get more value from re-using a more expensive guard?

4) How long will your plant need protection? Will the guard last this long?

5) Are they easy to erect?

6) Are they easy to maintain or replace? Will you still be able to access the plant for weeding, etc.?

Wind Breaks

Windbreaks divert wind away from an area and also reduce the impact of wind. In windy and exposed areas windbreak protection will enable plants to grow more vigorously, and create more comfortable outdoor living areas.

When designing and planting a windbreak consider the following points...

*The reduction in wind is determined by the height and width of the planting. Wind velocity is reduced for a distance from the windbreak of about 15-20 times the height of the planting.

*Dense plantings will provide greater wind control, however very dense plantings may have the opposite effect by creating an area of turbulence immediately behind the windbreak.

For this reason, it is best to create a windbreak which allows some wind to filter gently through the planting.

*Two or more rows of planting will give greater protection. Two or three parallel rows of plants of different heights can be very effective in reducing wind velocity (ie.plant a row of shrubs in front of a row of taller growing trees). Be careful to avoid plantings of larger trees that are bare low down or have been eaten by stock, or have self-pruned (because they are planted to close together). In these cases wind can be funnelled down near the base of the tress, actually increasing wind velocities at ground level beyond the wind break. Additional plantings of one or two rows of low growing plants will rectify this problem.

*For large exposed areas (eg. farm paddocks), staggered plantings are often effective.

Windbreak plants for warm climates:

• Acmena smithii
• Archontophoenix alexandrae
• Callistemon formosus
• Callistemon viminalis
• Callitris collumellaris
• Castanospermum australe
• Casuarina cunninghamiana
• Casuarina littoralis
• Eucalyptus tereticornis
• Eucalyptus tessellaris
• Leptospermum flavescens
• Melaleuca leucadendron
• Melaleuca linariifolia
• Melia azedarach
• Vitex ovata

Windbreak plants for cool climates

• Acacia longifolia
• Acacia pravissima
• Acmena smithii
• Agonis flexuosa
• Callistemon salignus
• Callitris collumellaris
• Casuarina cunninghamiana
• Coprosma repens
• Cotoneaster (various)
• Crataegus
• Cupressus macrocarpa
• Eucalyptus globulus "compacta"
• Juniperus (larger varieties)
• Ligustrum lucidum
• Melaleuca ericifolia
• Melaleuca nesophila
• Metrosideros excelsa
• Myoporum insulare
• Nerium oleander
• Photinia robusta
• Photinia glabra rubens
• Pittosporum (various)
• Tamarix
• Westringia glabra

Mulching

Mulching can be used to keep moisture in the soil, minimize erosion, keep plant roots insulated (hence stop them getting too hot or cold), and stop or slow weed growth.

Different types of mulches serve each of these purposes in different ways; so when choosing a mulch, you should first be clear on why you are using mulch. Mulches can be made with organic or inorganic materials, they can be thick or thin, repel water or absorb water, permanent or decomposing, and attractive or unattractive to look at.

Common mulches include timber products, leaf mould, paper and card board, sand and fabric.

Timber mulches such as bark, wood chip or sawdust generally look attractive, but they do change colour with time. Their effectiveness normally depends on how coarse the material is and how thick it is applied. To insulate the roots and control weeds well, they may need to be laid quite thick (ie. up to 25cm), but care should be taken building up mulch around the base of plants. This could promote collar rot or other diseases. Some timber materials may also encourage plant pests.

Paper or cardboard is an excellent mulch, and does not need to be laid as thick as timber product mulches. These materials can be covered with other more attractive mulch materials to create a better appearance. Stone or sand mulches do not rot down like organic mulches, and they do keep the air above less humid than organic mulches; but they can also reflect heat onto plants which may be a problem for some varieties, particularly when young.

There are many different fabrics which may be considered as mulching material; from old carpet underlay to synthetic fibre mulch mat produced specifically for weed control. These materials are often used under a thin layer of wood chip or stone, to give maximum affect.