Protecting Houseplants From Heat and Chill Damage

Providing your plant with the right temperature for it to thrive can be a problem. In modern centrally heated homes it may not always be possible to cater for the individual needs of each of your plants.

Chill-damageHowever, provided they are not too dry or the humidity too low, most plants can tolerate temperatures higher or lower than they would prefer. A few can tolerate quite considerable fluctuations in temperature.

  • In nature all plants are used to lower temperatures at night. For them a drop of a few degrees is normal.
  • Plants originally from temperate zones do not usually thrive in temperatures much higher than those in their native habitats. Their leaves are usually thin and are quickly affected by the drying effect of too much heat.
  • Even tropical plants can suffer heat damage. This is usually caused by heat not being counterbalanced by other factors that would exist in their natural habitats. Plants in tropical rain forests, where temperatures are often between 27-37°C (80-100°F), have extensive and cool root runs and a plentiful supply of water at the roots; they are also subject to high humidity.

Heat and chill damage to plants in the home occurs when temperatures begin to soar or fall, and the counterbalancing elements found in natural habitats do not exist without your intervention. In our homes the air is usually too dry and the pots and potting mixtures get too warm. Additionally, there is often not enough water in the mixture to meet the increased needs of the plants to counteract the effects of the high temperatures.

Plants accustomed to dappled shade are frequently placed on windowsills where full sun streams in — this can scorch their leaves. Similarly, in winter plants may suffer leaf damage at night if they are on windowsills.

Do’s and Don’ts

DO

  • Provide shade where necessary, using blinds, screens or curtains.
  • Create a free flow of air to lower temperatures, but avoid draughts.
  • Try to maintain the correct and ideal temperatures for all plants.
  • Increase humidity by misting or placing plants on trays filled with moist pebbles.

DON’Timage

  • Let water splash onto leaves. This may act as a magnifying glass in direct sunlight, resulting in leaf scorch.
  • Place shade-loving plants in full sun.
  • Subject plants to cold air in winter when you take them home.
  • Buy plants that have been standing out in a cold market in winter.
  • Water with cold water – use tepid water instead.

Heat damage

Heat damage is normally seen in summer and occurs in both indoor and outdoor plants. It varies greatly from plant to plant as some plants will tolerate higher temperatures than others. Two other factors are whether a plant has adequate water at its roots and how humid the air is. Both will offset the effects of the high temperatures.

Flower buds drop

In many cases the first signs of damage will be visible. At around 27°C (80°F). African Violets will drop their buds and fail to grow new ones at this temperature.

Increased transpiration

When the temperature rises the transpiration of water from the leaves increases. This is the only way the plant can lower its temperature naturally – by attempting to cool itself down. If it is very hot the plant can lose more water than it can take up through its roots. The leaves will begin to droop and if this continues over a long period the plant will dehydrate and wither. Even if the plant does not wither, it may be severely weakened and succumb more easily to pests and diseases.

Scorched leaf tipscorched-leaf

To offset damage caused by heat, ensure that your plants have fresh air (not draughts), adequate water and a high level of humidity in the air.

Heat and chill damage

Some plants can tolerate temperatures higher or lower than they would prefer, but many will suffer damage if they are subjected to extremes of temperature.

Cold damage

Even the briefest cold spell can cause some plants to die. Cold damage can also lead to poor development of roots and, later, lack of flowers.

Tropical plants don’t like cold, and they may die if they are too cold. If they are dry at the root itmay not affect them so badly. Clivias, for example, will survive if they are dry at temperatures down to 4°C (40°F).

When you transport plants home in cold weather see that they are properly wrapped. Don’t buy plants that have been standing outside in cold markets or in front of a florist’s shop. They maylook healthy at first sight, but they will probably deteriorate or not form flowers. Watering with cold water can give plant roots a slight check.

At night move plants away from windows into the centre of the room, out of draughts.

What to watch for

Heat damage

  • Plant leaves become thin and withered.
  • Potting mixture dries Out.
  • Scorched leaf tips.

Cold damage

  • Poor root development and lack of flowers.
  • Blackened leaves.
  • Plant collapses.

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