Not all annual and perennial flowering plants require pruning or deadheading (removal of spent flowers). Many are self-cleaning and can be left alone. Others, such as geraniums, petunia, salvia, lantana, daylily, and scores of other flowering plants will benefit tremendously from deadheading or a good pruning if they've stretched a lot by mid-summer. Deadheading flowering plants encourages healthier, bushier plants that produce more blooms.
There are a few plants such as coleus, dusty miller, fennel and basil, that if allowed to produce flowers will start to decline and might even die. That being said, if you want some of these to reseed themselves you can leave the flowers on the plants to allow them to drop their seed.
How To Deadhead
Deadheading is a simple task which takes a few minutes. If you've never dead-headed before here's how go about it:
First, keep a watchful eye on your flowering plants, paying close attention to blooms that are past their best. Once a flower has started to fade remove it from the plant with a quick snip from your pruners. Alternatively, if stems are thin or soft, knip it off with your thumb and forefinger. When doing this, try to remove just the spent flower leaving the new buds beneath intact.
The Many Benefits of Deadheading
Your flower beds and containers now look neater due to the lack of fading blooms, but how else has this deadheading process helped? By removing the spent flowers we stimulate more foliage growth - and more growth means more blooms. We have also prevented some plants from setting seed which, if they did, would trigger the production of a hormone which causes flowering to shut down completely. Some annual plants, such as Coleus should not be allowed to flower, otherwise you can expect decline of the plant. So, by our slight tinkering with Mother Nature, we can often force annual plants to produce more flowers and bushier plants.
Cutting Back at Time of Planting
Many annual bedding plants are grown commercially in what we often purchase at the nursery in "cell-packs". Annuals in cell-packs, or other smaller size containers, will often "stretch" as a result of growing in such a restricted environment with limited soil. When planting annuals that have become stretched, or leggy, in the pots they were grown in, it's a good idea to cut them halfway back at planting time. Yes, your impatiens will look like green stumps, and you will most likely be cutting off all the blooms, but, once planted, it won't take long for them to flush back out into fuller and bushier plants than they would've been with no cutting back.
Cutting Back During Summer
By mid-summer, if an annual or perennial plant growing in a bed or container has become leggy and unproductive, simply cut it back. The amount of foliage you remove will of course depend on the size of the plant. When you cut a plant back, make sure you don't cut back to a point in which there are no leaf buds left. This being said, whenever in doubt about how far you can cut back any specific type of plant always consult with your local nursery and garden center professional or a pruning expert.
At any time during the warm season it is okay to cut back dead or ugly foliage.
Winterizing Your Annual and Perennial Beds And Container Gardens
The best way to winterize an annual flower bed or container garden is to plant Pansies and other colorful cool-season annual plants in it!
Otherwise, if you don't intend to plant Pansies or some other cool season annuals, remove summer annuals that have finished their bloom cycle, and/or are dead or dying, from the beds or containers they are growing in. Leaving these plants in beds or containers throughout the winter can lead to development of damaging fungus and disease.
When grown in containers, some annual plants can be overwintered indoors. Before bringing any outdoor plant inside your home, inspect all foliage, stems and soil for insects. If insects are present, pick them off, or wash them off with water from the garden hose.