Heat zones are sometimes used here in Australia and are something that should be used far more frequently. A heat zone is defined as the number of days above thirty degrees Celsius in a given year. As much as some plants cannot cope with frost and excessive cold, others cannot cope well with extreme heat-this varies for each species.

Within Australia, I am of the view heat zones are very useful for two main reasons. The first is that the climate within Australia is often hot and dry. The excessive heat (like the several days close to forty degrees Celsius we have had this summer, that’s just finished) can cause plants to suffer from physiological damage in some way due to degrees over thirty degrees.

Another reason here in Australia is that there are a lot of people in this country still think that a perfect lawn with English style plants around, or within the lawn, are the way to do gardening. What such people don’t think about here is that plants used in traditional ‘English gardens’ aren’t suitable in Australia in most cases. While this attitude is changing slowly, I still see it expressed at work with certain clients, unfortunately.

I do think that the idea of heat zones is a good one, and need to be used more widely here in Australia. I’d love to be able to start conversations with clients as to why some plants are advisable in certain situations and others aren’t (and not just because of too much heat, but for many other reasons too). If they can be given some understanding, it does make the job easier, especially if they can see what you say works. This isn’t encouraged where I currently work unfortunately!

When growing fruit and vegetable plants, the number of growing days are important too. This is the heat needed for fruit to ripen. I live in Sydney, which is classed as warm temperate with 240 growing days.