The late January heatwave in the southern states of Australia has seen a spate of calls to talk-back gardening shows regarding burnt foliage. Melbourne experienced three days in a row of 43º including one day at 45.1 º and Adelaide had 6 days over 40 º with one day at 45.7 º. Even in Tasmania records were set with the town of Scamander reaching 42 º. Authorities were citing the heatwave as a one-in-100-year phenomenon. Or perhaps it was as a result of global warming!

Many plants have been burnt during this extreme weather and naturally gardeners want to know if they should be doing anything about it. A quick walk around my garden showed me the result of the heatwave upon the foliage of the following plants.

Bay Tree (Laurus nobilis) – my 10 year old potted specimen has many brown leaves or brown patches on leaves.
Jellybeans (Sedum sp.) – a potted specimen looks like it has been blowtorched.
Purple Barberry (Berberis atropurpurea) – many leaves have completely frizzled
Hebes – many of my hebe collection have black leaves or partially blackened leaves
Dwarf white agapanthus – reduced to a mass of bleached withered foliage.
Roses – are exhibiting brown leaves
Strappy plants like lomandra and dianella have rolled their leaves and leaf margins have browned off.
NZ Flax (Phormium sp.) – older leaves have died, remaining leaves are rolling inward.
Aeonium – normal summer dormancy means the outer leaves of the rosettes have been scorched.
Euphorbia – a carpeting species has almost completely browned off.
Oaks/Elms – the foliage of newly planted street trees has crisped and will soon be shed. Some older trees have been affected too.

Discussion amongst my colleagues has resulted in us all agreeing to treat burnt foliage like frost damaged foliage – don’t prune it off! The burnt leaves are protecting the unmarked leaves beneath and pruning may encourage the production of tender young leaves which you do not want because there will be more hot weather on the way. Possibly plants that were burnt were drier than unmarked plants. Try and get some water to the burnt plants to aid in their recovery. Remember deep watering is better than sprinkling the surface. Do not cut trenches around trees! This damages the surface roots. Creating a temporary levee or low bank around a valuable tree is a better method of retaining water until it soaks in.

Most plants will recover from this heatwave. When the weather cools and when/if we get some rain they will be encouraged to put on some new growth as burnt foliage is shed. Deciduous trees that shed leaves in summer may or may not produce a second crop of leaves – it depends on how much water they receive. They may well go dormant until next spring so don’t give up on them just yet! Try not to get too despondent over the state of your garden. Take it all as a learning experience. I heard Richard Barley the Director of the Royal Botanic Gardens in Melbourne on ABC local radio last night. He said “we do learn a lot about plants in these conditions. It’s great to be able to observe and learn about plant tolerances.” He also urged gardeners to group plants according to their water needs – it really is a bit silly to be always watering one plant in the middle of a garden bed because it wilts every second day. If it needs that much water it is clearly in the wrong place and you should consider moving it to a moister/shadier area or removing it altogether.

Don’t forget mulching is a great way to lock in moisture, reduce weeds and it keeps the soil cooler. Lastly don’t fertilise any burnt plants. This will just encourage new growth that will be susceptible to the hot sun. An application of a seaweed solution could be beneficial as this is a general plant/root tonic and not a fertiliser so you can use this with confidence.