Understanding when and how a frost forms is the first step into preventing the damage it can cause. The worst frosts tend to occur on a cloud-free (clear) night with very little to no wind. Why is this? On still nights with no wind and no clouds, the ambient air cools down very quickly due to the lack of heat in the atmosphere. However, when a frost is expected and there are clouds and a slight wind, the clouds act as a buffer and slow the loss of heat in the atmosphere.
How do you prevent frost damage in the home garden?
Preventing frost damage in the garden can sometimes prove to be a little tricky, but there are some easy ways to keep yourself prepared!
Always pay attention to the forecast! The Bureau of Meteorology (BOM) website has a lot of great information which can provide the home gardener with current weather forecasts which are relevant to the Australian climate.
Cover up! Covering tender plants such as young seedlings, annual flowers, vegetables and herbs can prevent their foliage from being burnt in the peak of a frost. Cloak soft foliage and frost sensitive plants as they are more likely to be affected from heavy frosts. Drape cloths over garden-beds that are most likely to be affected.
Softer perennials, Hebes, being covered to prevent frost damage.
Get up, beat the sun and water! The most damage caused from a frost is when plants are still covered in ice and the sun shines on their foliage. Soft foliage plants will go translucent and can even turn black! The best prevent damage is to lightly water plants which are covered in ice before the sun hits their leaves. Shown below is a before and after photo of some oregano which was heavily affected by the frost. I watered the foliage with a hose on low pressure, the water temperature melted the ice without causing any damage to the plant. If the sun has already started to shine of affected plants it is always a good idea to still mist/water the foliage to help reduce the chances of further damage.
Choose tough! If the area you live in an area which is known for experiencing heavy frosts try and avoid planting frost prone varieties.
Move pots and containers! Container gardens that can be moved and re-located under under-covered areas will prevent frost from settling on the foliage.
My plant is frost burnt, what do I do to fix it? Knowing when to prune?
When a plant is damaged by frost there is usually two main symptoms. The first symptom is the most obvious, affected plants leaves turn black and begin to wilt. If the foliage is black and the main stems are still green, cut the plant back to the healthy green stems. If left un-pruned plants are at risk from rot, fungal diseases and stem die back. Once cut back, if in a pot, move to a frost protected position. Otherwise if the plant is in a garden-bed make sure to cover the plant if another frost is expected. But in most situations when the leaves turn jet-black, especially annual flowers and vegetables, it is not uncommon for the plant to eventually die.
The second symptom is more common on perennial plants with thick robust foliage, such as Ficus and Syzygiums. Affected plants will have their foliage will turn brown/copper. Pictured below is a Metrosideros bush which was burnt by the recent frost. In this case I wouldn’t prune the affected foliage until the end of winter. The reason being, the affected foliage will act as a buffer for any future frosts and will protect the healthy leaves which are hidden below.
As you can see in the second photo there is plenty of healthy leaves below the damaged foliage. This Metrosideros will make a complete recovery once pruned in the spring!
The last symptom is translucent foliage. These symptoms can be instantaneous or it can take a number of days until the symptoms appear. Affected plants also start to wilt and it is best to avoid pruning until the final frosts in late winter pass. Plants that are affected are likely to recover.
I hope that this guide to beating frost can be helpful to your adventures in your garden!
Until next time happy gardening!
By Bonnie-Marie Hibbs