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Preventing sunburn in your plants

Going.Local
Published on October 26th 2020
13

by CandideUK. All rights reserved

A close up of a flower
The recent heatwave that hit the country made some gardeners anxiously look towards their garden. Many plants that flourish in full sun can decide to wither in high temperatures.
So to help you save your plants, we will highlight common mistakes, how to identify sunburn and ways to avoid/treat a stressed plant.
A sun stressed cotyledon
A plant that is gradually exposed to more sun will go through a process of changing its pigments from green to red.

What is sun stress/burn?

If you just spent three months indoors and I ship you off to a beach in the Bahamas (with no sunscreen, hat or clothes) you will quickly turn into a crayfish aka sunburn. Similarly, plants adapt to sunny conditions over time.
Common questions:
  • What is sun stress?
It is when you place a plant in a sunnier area than it has been growing in up to that point and the leaves change colour or crisp up due to dehydration.
Check out this post by @ernstvanjaarsveld on sun stress in succulents.

ernstvanjaarsveld

New leaves are often red in pigment - a sign of stress in the harsh sun or new environment they are exposed to, but as they harden off, the green color returns. Make sure you help the new leaves in recovering by moving a pot if you can, or adding a bit of extra shade for lithops seedlings. Some plants like roses are tough enough to recover quickly and other are chosen for this trait like Cunonia.

  • What is sunburn?
Sunburn occurs when the plant is exposed to too much sun causing the cells to start to die, causing the exposed area to turn pale and then brown before eventually shedding the leaf.
  • Why do some people stress their plants?
It is possible to change the colour of the foliage of some crassulas, aloes etc. by providing less water or more sun. The reddening is a change in pigment (like a tan) that helps the plant. Stressing a plant for colour should be done gradually in spring. It may slow the growth, but will not harm the plant necessarily. It does mean you will have to keep a closer eye as it is close to its limit.
  • Can I plant a nursery plant with a full sun tag in full sun immediately?
If the plant has been in full sun, outside without any colour change or fading in the leaves, then the answer is yes. If you have left said plant under an awning for a couple of days before planting it, it will need time to adjust.
Kalanchoe with red stressed leaves
Some plants have naturally red foliage that can become a deeper red in full sun. If the sun is to intense, the leaves will fold in to minimise exposure.

Things to avoid

Your plant has effectively damaged its skin and is now very vulnerable to pests and diseases. If it has a healthy root system and some leaves left, then it can still bounce back.
Some things to consider:
  • Lay off the water a bit.
  • Do not water any plants in the warmest part of the day.
  • Do not add fertiliser.
  • Be extra careful of pests.
  • Do not add any pesticide or chemicals that would further stress the plant.
  • Do not repot unless absolutely necessary.
  • Complete shade is a no-go.
Areas with exceptions:
  • Some orchids need higher humidity and more frequent watering when temperatures rise but do not mist/water leaves if the orchid has a burn.
  • Plants that require being waterlogged like some Alocasia.
Given time, the sunburnt section will die off on its own. If the leaf looks unsightly, then some tend to remove it. Note that if you remove it by cutting into the stem or healthy leaf, your stressed plant now has an open wound. In the case of succulents, it would be best to give them time to form a scar and reduce watering until you observe active growth.
A sun stressed crassula

How to treat sunburn

This will depend on the plant in question (tropical, subtropical, succulent etc.). Some will require keeping the plant moist while it recuperates, others will not.
Start off with the following steps:
  • Move it to a shadier spot.
  • Identify your plant give Plant ID in the Knowledge tab a go!).
  • Look up the care instructions. Does it need constant water, to be kept moist, watered weekly or monthly?
When to water?
  • If the soil is bone-dry and the pot has cooled down or it is early morning and the soil has not heated up then you can water it.
  • Make sure the water is the same temperature as your pot (room temperature or outside temperature).
  • Do not shock the plant further by placing cold or extremely hot water on it.
Give it time to mend. Your plant, like your body, will need time to recover from a burn. Removing the burnt area before the plant is ready will expose it to diseases. Best is to let it shed the leaf naturally.
Succulents will sometimes carry the scar indefinitely. This is why it is important to avoid sunburn from the get-go. The process of recovery will depend on how burnt the original plant may have been. It may be that the entire plant suffered and that it will use reserves to push out new pups from the base. Just be patient.

Guidelines to help improve your ability

Here are some tips on how to avoid sunburn in the future:
Tip 1 | Know where in your garden and home is the sunniest. South-facing windows get more sun than North-facing windows.
Tip 2 | Sun exposure is harshest in summer. You can rearrange your plants in late spring to move them away from the harshest sun and move them closer in winter.
Tip 3 | Watch for heatwaves
  • Moving plants or covering them or in the case of some tropicals increasing humidity will help them during heat waves
Tip 4| Consider having moveable features in your garden.
  • Wooden stumps or ornaments that can provide partial shade during the hottest summer days and be moved in winter.
  • Plant taller sun tolerant plants or annuals to shade out prone species in summer.
Last but not least, if you have an indigenous garden, then you might want to consider leaving those lovely summer grasses (e.g. quacking grass and hare's tails grass) to sprout. They dry during summer, reflecting most of the sun and protect smaller species. The roots die off towards the end of summer, allowing you to remove them with ease.

Hope this could provide you with some help and a bit of encouragement to keep going. Remember to share your progress!

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