Heat wave help

recycled juice bottle

 

With high temperatures predicted for many areas of mainland Australia this week, I would like to remind you that you can find tips on helping your garden to survive extremely hot temperatures here: Heat wave protection

Watering in drought conditions

This week, two readers have asked me about garden problems caused by lack of water. As you know, it is extremely difficult to keep gardens well-watered in drought conditions. However, as plants can only absorb the nutrients they need for healthy growth and ripeness of crops as water-soluble ions, inadequate water is the cause of a wide range of problems, including pest attack.

Bare soil in garden beds and around trees, shrubs and vines allows a lot of soil moisture to be lost to evaporation. A 5 cm layer of organic mulch over beds and around larger plants (keeping it a hand span from the trunk) will prevent water applied to the soil from being wasted. Lawns are greedy and as their roots are close to the soil surface, they take water and nutrients intended for fruit trees and favourite ornamentals. Keep lawns beyond the outer canopy of trees and cover the area under trees with mulch.

wtrbttle.jpg A method that we have found very helpful to water mulched beds is to use plastic soft drink and juice bottles to funnel water through mulch directly to the root area of susceptible plants. This is a quick and very efficient way to hand water during drought, water restrictions, heat waves or windy weather. Limp tomato seedlings will freshen up in about 10 minutes after watering by this method.
Simply cut off the base of each container, remove the lids and bury the necks of the containers about 8 cm deep near outer edge of the foliage of plants. Large shrubs may require several containers. Pour water into the container until it begins to drain slowly – an indication that you have dampened the soil in the root area.

Seedlings and pot plants are usually the first to suffer during heat waves, and you can find advice on how to revive stressed pot plants here: Pot plant stress

Windy weather update

Transpiratiion Predictions are for more cold, windy weather on the way. Keep a close watch on your garden as wind can dry out soils faster than summer heat, resulting in cell collapse of soft tissue plants. To discover why this happens and how to protect your plants, see: Windy weather
Seedlings and many vegetable crops are vulnerable to wind damage in winter and early spring. Ripening citrus are also easily damaged by strong winds.

Heat wave protection

Some parts of Australia are enduring extremely hot weather and, apparently, there is more to come this summer. Periods of intense heat can cause scorching in many gardens.
Although European-based garden texts recommend full sun for most vegetables, where summers are hot and air pollution is low, full sun can result in sunscald. While Australian natives have evolved to restrict loss of water through leaves in hot, dry conditions, very hot plants, especially those that originated in cooler Northern Hemisphere regions – such as most of our vegetables and fruits, lose a lot of water through their leaves in an effort to keep cool, in a similar way to humans perspiring.

A bit of shade
shdeclth Providing some light shade during the hottest part of the day can prevent sunscald on susceptible crops, and, by keeping the plants cooler, reduces their water consumption, an important consideration where water restrictions apply. We use lightweight, knitted shade cloth, supported by arches made from 38 mm irrigation pipe attached to garden stakes or star stakes, or you can use old light-weight curtains or sheets.
Each canopy is positioned to allow morning sun to reach plants, yet not restrict air flow around them. Poor air flow (such as in fully enclosed areas) can produce conditions suitable for some fungal diseases to establish. Instructions for making these can be found in the post Sun and heat protection.
However, in an emergency, any old curtains or pieces of lightweight fabric will do. Tie the corners to garden stakes to provide some relief for garden beds during the hottest part of the day.
If possible, move potted plants to a shaded area of the garden, and group them together. This provides more humidity around the plants, and reduces their water requirements.

Water is essential
wtrbttle.jpg Adequate soil moisture is essential for your vegetable garden to maintain good growth during heat waves. Mulching garden beds is very helpful. A method that we have found very helpful to water mulched beds is to use plastic soft drink and juice bottles to funnel water directly to the root area of susceptible plants. This is a quick and very efficient way to hand water during water restrictions, heat waves or windy weather. Limp tomato seedlings will freshen up in about 10 minutes after watering by this method.
Simply cut off the base of each container, remove the lids and bury the necks of the containers about 8 cm deep near outer edge of the foliage of plants. Large shrubs may require several containers. Pour water into the container until it begins to drain slowly – an indication that you have dampened the soil in the root area.
Seedlings and pot plants are usually the first to suffer during heat waves, and you can find advice on how to revive stressed pot plants here: Pot plant stress

Water for wildlife
Birdbath Don’t forget to provide water for birds and bees that visit your garden. A bird bath, or containers of clean water positioned where cats and dogs can’t reach them will provide relief for the insect-eating birds and the bees that pollinate your crops. Chlorinated pool water is toxic to these helpful creatures. A container of water under shaded foliage will be appreciated by your resident frogs too.

Coping with heat waves

Heat waves place extreme stress on gardens when plants lose lots of water through their leaves in an attempt to keep cool and retain humidity around their foliage. You can help reduce moisture loss by providing some temporary shade over sensitive plants in the vege patch and ornamental parts of the garden.
See also: Sun and heat protection

However, seedlings and pot plants are usually the first to suffer in heat waves, and these may need watering twice a day until weather returns to normal. If potting mix dries out, the first sign may be complete collapse of a plant. If you water dry potting mix in the normal way with a hose or watering can, your plants may not be getting as much water as you think. This is because potting mix shrinks slightly when it dries, leaving a narrow gap between the mix and the pot. When you water, most of it runs into the gap and out through the drainage holes, leaving the mix around the roots still dry. Seedling punnets and smaller pots can be thoroughly watered by immersing the entire pot in a bucket half filled with water, or use a laundry tub if a lot of pots need reviving.

Water should come over the top of the pot. Leave the pot in the water until bubbles cease to rise. Short term immersion won’t hurt the plants. Then lift the pot allowing it to drain into the container. This method of watering also works very well when your water supply for plants is strictly limited.
For pots too large to be immersed in a container, fill some large soft drink or juice containers and insert 2 or 3 neck down into the potting mix. Provide support if necessary and allow them to empty slowly into the mix. Re-fill the bottles and repeat watering until water is being drawn into the mix very slowly. If heat is likely to continue for some time, place some mulch or stones on the surface of the potting mix to slow evaporation.

Sowing and planting tip

When sowing seed directly into garden beds, or when planting out seedlings, or planting shrubs and trees, always make sure that soil in the growing area is thoroughly dampened BEFORE sowing or planting. Then, after sowing or planting, you only need to add enough water to settle soil around the seeds or roots. Soil should be what is known as “dark-damp” before you add seeds or plants.
This practice is very important because, if soil in the growing area is relatively dry and you only apply water to the seed row or plants after you put them in the soil, some of the water you apply will be drawn away from the seeds or plants into the surrounding drier soil. The dispersion of water into drier soil is a common cause of germination failure, or seedlings, shrubs and trees drooping several days after planting.
When sowing seed, or planting out seedlings, thoroughly water the furrows or planting holes first. Check that you haven’t just wet the top centimetre of soil. For successful germination, soil must remain dark damp, and a very light application of fluffed-up organic mulch across the growing area or between rows can help prevent water loss through evaporation. Seeds sown in dark-damp soil don’t usually require soaking before sowing, with the exception of silver beet and beetroot as these have a thick, corky outer layer. If legume seeds are sown in dark-damp soil, they do not require soaking beforehand because over-wet legume seeds may rot before germination.
When planting shrubs, trees and vines where soil is not dark damp, fill the planting holes with water and plant only after the water has drained away. After planting, apply enough water to settle soil around the roots and apply a 5-7 cm of organic mulch to prevent water loss through evaporation.

Heat wave first aid

A lot of Australian gardens are suffering from a prolonged spell of very hot dry weather.
Garden beds that contain a moderate amount of organic matter will handle the extreme conditions better than most, as organic matter in soil keeps soil more moisture retentive, especially if mulch is also applied to the soil surface.
• Avoid watering in the middle of the day. Water early or late in the day. If watering in the afternoon, first check that the water in the hose has not reached a temperature that will scald plants.
• Try to give vegetable beds and precious shrubs a deep watering rather than a light daily hosing, and only repeat watering when the top cm. of soil becomes dry. Daily hosing usually only wets the top centimetre, or so, of soil, encouraging plant roots to stay close to the soil surface, making them more prone to wilting in hot weather.
• Apply a thick layer of mulch to all beds, if possible, as this will prevent loss of soil water through evaporation. However, avoid mulching beds close to buildings in areas where bush fires are a risk.
• Provide a temporary shade canopy for beds or plants that appear stressed. Use whatever is available – shadecloth, tarpaulins, old curtains, etc. Shading them will reduce water loss through the plants’ leaves, and plants will require less watering. Plants release moisture through their leaves in an effort to keep cool, in a similar way to our perspiration.
• If possible, move potted plants and seedlings against the south side of a building, where it is cooler. The mix in pots can become much hotter than soil in beds, and potted plant roots can become permanently damaged in this type of weather.
• Place pots close together as they will create group humidity, keeping them cooler.
• Avoid fertilising in this weather, unless it is seaweed tea applied after a deep watering. Fertilising when soils dry out quickly increases the risk of fertiliser burn and makes plants less able to cope with adverse conditions.
• While you can leave burnt foliage on plants and the plant will usually recover when temperatures cool and watering is adequate, if a favourite evergreen shrub or citrus tree is extremely distressed, prune it back – leaving some foliage so that it can manufacture food. This can help the plant to provide water more efficiently to the remaining plant. Leave the prunings as mulch around the base of the plant. However, pruning of deciduous plants at this time of year can cause excess sap loss (bleeding) in some varieties, such as grapes, pecans, mulberry.
• Give flowering annuals lower priority if water is restricted – these can be easily replaced when conditions are more suitable for growth.

Tomato problems

From e-mails I’ve received, it appears that some gardeners are having problems with their tomato plants. When tomato plants become water-stressed in prolonged hot, dry conditions that are affecting some parts of the country, they are prone to attack by fruit fly, heliothis moth caterpillars (corn earworm) and blossom end rot.
Blossom end rot is caused by calcium deficiency, and is not a disease. Like us, plants need a good balance of calcium and magnesium to form a strong structure. Calcium and magnesium are required for growing tips of plants as well as fruit production and, if there are not enough of these nutrients to go around, growing tips will get priority. Calcium deficiency can occur in several different ways.
Most commonly, it occurs when soil is too acidic (soil pH less than 6) and there are insufficient calcium ions in the soil. Rarely, it also occurs in extremely alkaline soils (soil pH above 9) where calcium becomes insoluble, and plants are unable to absorb it.
In soils with a suitable pH of 6 – 7.5, erratic watering can cause it, as plants are unable to absorb nutrients from dry soil, when needed.

To avoid this problem, ensure that your tomato, capsicum or chilli bed has a suitable soil pH before planting out seedlings. See Changing soil pH. If your soil is slightly too acidic, and the problem has already occurred, you can raise soil pH slightly by dissolving a generous handful of dolomite (a mixture of calcium and magnesium) in a full watering can, and apply this around the root area (under mulch) of each plant – one full watering can per plant. If you know that your soil has plenty of magnesium, use agricultural lime instead. This treatment will take several weeks to work, so good bed preparation is worth the effort.

Tomatoes will benefit from being protected by a thick layer of mulch to reduce fluctuations in soil moisture, and a thorough soaking (under mulch) two or three times a week during dry weather, rather than a light daily watering. Avoid overhead watering of tomatoes.
Hot days increase transpiration (water loss) from plants in the same way we perspire to keep cool. Setting up a light shade cloth canopy over the tomato bed will reduce water loss from plants and help prevent water stress and sun scald on fruit. Tomatoes will ripen under light shadecloth in hot weather. A soil feeding of seaweed extract ‘tea’ can also help plants build resistance to adverse conditions, including drought.
Mosquito netting over plants will serve two purposes. It will prevent attack by Heliothis moth and fruit fly, and provide a light shade for the plants. Modern tomato varieties do not require insects for pollination. If older varieties cease to set fruit, flowers can be hand pollinated with a dry watercolour paint brush.
In some areas, the netting may be enough to slow transpiration, without the shade cloth. All fruit affected by grubs or caterpillars should be collected and fed to the chooks, or placed in a sealed black plastic bag and left in the hot sun. This will kill the larvae and break the breeding cycle. Never compost fruit that contains grubs.

When to water?

A common question asked by gardeners is how often should they water their garden.
Unfortunately, limited watering times imposed by water restrictions have encouraged some gardeners to rush around giving everything a light watering during the allocated time.
A light daily watering is one of the worst things you can do for your garden. It only encourages plant roots to stay close to the soil surface – the area that dries out first.
Plants watered in this way wilt quickly on hot, or windy, days – encouraging gardeners to perpetuate the cycle.
If you use mulch, very few plants need watering every day. Mulch not only prevents water loss through evaporation from the soil surface, it assists the capillary movement of water through soil. Seedlings will probably require daily watering through the warmer months because they have very small roots systems.
The most reliable way to decide if plants need watering, is to poke a finger, up to the first joint, into the soil or potting mix. If the soil feels damp, the plants don’t need watering. If the top centimetre or so feels dry, give the plants a thorough watering, under the mulch. When watering shrubs and trees, water under the outer edges of the mulch where the feeder roots lie, not near the trunk. Plants watered in this way develop stronger root systems, and will be more resistant to adverse climate conditions.
Many plants slow their growth or become dormant in winter, and they need less watering than in warmer months. More pot plants are killed by over-watering, than under-watering. When the surface of potting mixes feel dry, small pot plants can be watered, at any time, with water collected while waiting for the shower to warm, as long as you remove the bucket before getting in the shower and making the water soapy. Dunk the pots into the bucket until bubbles cease to rise from the water surface. Overhead watering of indoor plants can encourage fungal diseases, especially in the cooler months.