In fact, they’re fenced in by the amount of soil in the pot and what you provide them with for feeding.
If you’re a plant mum or dad, think of fertiliser as the other half of your potting soil.
When potting soil is fresh, your plants won’t need much – if any – fertilising.
This is especially true with modern, fortified potting soil which often has fertiliser and other nutrient enhancers mixed in.
After about two months, however, the plant will have consumed the nutrients in the soil so you’ll have to fertilise it if you want continued, healthy growth.