This is a question often asked by gardeners for a number of reasons. It may be when leaves change colour, get scrappy, wilt or fall. There may be no flowers or fruit, the plant may lack vigour, it may have pests or diseases, or it may be struggling, or have died. The best way to solve plant problems is to ask yourself a series of questions which usually produce an explanation. Ideally you should know your plant and know what it likes as this will identify factors that affect its performance.
The major things to think about are climate, ideal position, preferred soil type and pH, its water and nutrition requirements and finally, its life cycle.
Climate is pretty straight forward. Does the plant naturally grow in a Mediterranean climate like here in Adelaide, or is it arid, temperate, tropical or subtropical. Having recently spent some time up in Brisbane and surrounds I was interested to see the number of plants which grow well there as well as here, but also envious of the subtropical plants which they grow well and we struggle with. It is also important to understand that there are a number of subtropical or at least warmer climate plants which we are able to grow here in Adelaide however they need to be planted when the ground is warm, rather than into cold soil. These include frangipanis, hibiscus, passionfruit and citrus. Planting them in the middle of winter will give them a big setback, cause them to struggle and maybe even die.
The position the plant prefers refers to whether it grows best in full sun, semi-shade or full shade, and whether it likes a sheltered position protected from winds or it is happy in an open exposed situation.
Soil preference is also very important as many plants require well drained soil and as such only thrive in sandy or loamy soils, and will struggle in heavy clay soils. Does the plant prefer to be kept moist or is it hardy and water wise, and tolerant of brief periods of drought? Does the plant come from soil which is naturally rich and fertile? If this is the case does it require regular feeding, and if it does require feeding are there special requirements such as native plants which require fertiliser suitable for their needs? The pH the plant requires is also really important in Adelaide as plants such as camellias need to grow in acid soil and as most of Adelaide has neutral to alkaline soil, the pH must be adjusted to make it more neutral to acidic.
Plant life cycle
It is important to understand the life cycle of your plant. One basic thing is whether the plants is deciduous or evergreen. Many gardeners have been caught off guard by their new plant losing its leaves only to find out that it is normal and is simply deciduous. Similarly if a plant is annual it will die within a year while perennial plants keep going year after year. Just to complicate this slightly some plants are perennial but herbaceous which simply means that all the above ground parts of the plant die off but it will reshoot next season from the base.
Knowing when your plant flowers is very important as it influences when and how you should prune it. For example, most people know that roses must be pruned in winter, however this is only true for repeat flowering roses which bloom from spring to autumn. If you happen to have a spring flowering rose, which only blooms the once in spring and you prune it in winter you will be cutting off the flowering wood and won’t get any flowers. Understanding what wood or growth the flowers appear on is also important. For example many plants flower on new wood so pruning them hard stimulates more new growth and hence more flowers.
In most situations when you go through this list of questions, the answer becomes obvious…………… but not always!