Not all annual plants require pruning or deadheading (removal of spent flowers). Many are self-cleaning and can be left alone. Others, such as geraniums and petunias, will benefit tremendously from deadheading, or a pruning if their branches have stretched a lot by mid-summer. There are a few annual plants, such as coleus and dusty miller, that will decline rapidly and eventually die if they are allowed to bloom. So you want to make sure and snip the flower buds off these before they ever open. There are some annuals that will reseed themselves. If you want them to do so, you don;t want to snip off their dead flowers at the end of the season.
Your flower beds and container flower gardens will look neater when you deadhead spent flowers. But there are other benefits. By removing the spent flowers we stimulate more new foliage growth - and more foliage growth means more blooms. We've 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. So, by our slight tinkering with Mother Nature, we can often force annual plants to produce more flowers and bushier plants.
Pruning & Deadheading Instructions
How To Deadhead
Deadheading is a simple task which takes only 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 by pinching it off with your finger tips or with a quick snip from your pruners or snips. Alternatively, if stems are thin or soft, nip it off with your thumb and forefinger. When doing this, try to remove just the spent flower leaving the new buds beneath intact.
Cutting Back
At planting time: We often purchase annual flowers in small pots or "cell packs." Plants in such small pots have a short shelf life at a nursery. When in the small pot for too long plants 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. Make sure to leave some leaves on plants. Yes, your impatiens will look like green stumps, and you will most likely be cutting off all the blooms, however, once planted, it won't take long for them to flush back out into fuller and bushier plants than they would've been had you not cut them back.
During the growing season: At any time during the warm season it is okay to cut back dead or ugly foliage. By mid-summer, if an annual 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 on the branch.