Understanding How Plants Grow and Reproduce
A basic understanding of plants underpins everything you do in the garden. Are you planting annuals for just one season, or a shrub or perennial that will become permanent? Knowing how plants reproduce also helps you maximize their contribution to your garden.
Annual plants complete their life cycle in a single growing season: growing from seed, flowering, and then dying. Removing fading flowers before they get a chance to set seed tricks them into producing more and lengthens the floral display.
Hardy annuals, such as pot marigolds, nasturtiums, and candytuft, will germinate outdoors and can be sown in the fall to overwinter as young plants for early summer flowers but are usually sown in the spring as soon as soil conditions allow. Half-hardy annuals require indoor warmth to germinate and are transferred outdoors after the risk of frost has passed. This group includes most traditional bedding plants, such as petunias, salvia, and French marigolds. Biennials, such as foxgloves and forget-me-nots, usually complete their life cycle in two years. Seedlings appear in summer and then overwinter before producing flowers in spring or early summer, then setting seed and dying.
What Are Perennial, Annual and Biennial Plants?
Perennials live on from one year to the next. The term is mainly used to describe non-woody herbaceous plants like delphiniums and geraniums, which die back in winter and reshoot in the spring. Tender perennials, such as pot geraniums, also survive from year to year if kept in temperatures above freezing. On the other hand, annual plants, such as nasturtiums (Tropaeolum), reproduce by setting seed before they die at the end of their life cycle. You can collect seed from your annuals to sow for new plants the following year.
Unlike annuals, biennial plants require two growing seasons before blooming. Foxgloves (Digitalis) are just one example of a biennial plant that sets seed before the end of their two-year life cycle. Be sure to pinch off any buds that form in the first season to ensure a good display.
Pollination and setting seed is by far the most common way by which flowering plants reproduce in nature. Most garden flowers, fruits, and vegetables are pollinated by insects, particularly bees, but grasses, conifers, shrubs and trees with catkins, and crops like sweet corn are wind pollinated.
Pollination is a method of sexual reproduction and therefore means that a variety of genetic combinations are possible and the resulting seedlings can vary. Although some flowers are self-pollinating, which means they do not need to receive pollen from another flower to reproduce, cross-pollination or cross-fertilization ensures a good genetic mix, giving plants in the wild a greater chance of adapting to their environment.
In horticulture variation is what enables plant breeders to select and produce cultivars with new combinations of desirable characteristics. Commercial seed production is carefully controlled to minimize this genetic variation and produce predictable results that retain these characteristics. F1 seed is the most uniform and the most expensive, followed by F2 and the cheaper, open-pollinated strains.
As well as pollination and seeding, plants use a number of other ways to reproduce at ground level and beneath the soil. Runners, rhizomes, bulbils, and offsets are all “vegetative” or “asexual” means of reproduction that are useful for gardeners, because the plants produced are normally identical to the parent and produce garden-ready specimens quickly and easily.