Understanding plant life cycles

Finally, Alan considers perennials, living for three years or more. Within this group he looks at herbaceous plants, woody perennials and those with underground storage organs such as bulbs, corms and tubers.

Watch now, for a quick guide to plant life cycles.

Understanding plant life cycles: transcript

As well as giving plants botanical names, we tend to classify them according to their length of life, and we group them under three main headings - annuals, biennials and perennials.

Annuals are those plants that last for just a year. Their entire life cycle is completed within a 12-month period, a bit like the Beano annual. Here's an example. This is a little viola, or heartsease. Now, ironically, if you leave this in the ground, it can carry on for a couple of years, maybe even longer but we treat it as an annual. We sow it one year in the spring, it flowers and then it either dies or we pull it up. That is what an annual is, completing its lifecycle within one year.

A biennial, like this foxglove, is sown one year, to flower the next. And with foxgloves and sweet williams and wallflowers, we tend to sow them in May or June. They grow into bushy squat plants through the winter and then the following spring and summer they burst into flower. Its life cycle takes the better part of two years
and then it will die. A plant which lives longer than that, three or more years is a perennial.

Plants like this Thalictrum are herbaceous perennials. Herbaceous means they die down to ground level every winter and you can take off the dead foliage at the top. But being perennial, they will keep coming up from below ground every year.

Then we get woody perennials, shrubs, we call them, like this rhododendron. Many stems, generally not growing terribly high. When they grow very high, we call them trees; and trees and shrubs can be either deciduous, losing their leaves in winter, or evergreen, keeping them the whole year round.

Some perennials like this allium or ornamental onion, don't just have roots underground that keep them going. But they have big fat storage organs called bulbs, corms and tubers, all a means of making sure their lives extend year after year. And then there are the plants that adapt themselves to reach the sun, where they might otherwise have difficulty in getting there. They are the climbers. Plants like clematis, which will cling to support systems and throw their faces up to the sun, especially on a day like this.