The onset of fall doesn't have to mean the end of all of those beautiful, colorful annuals you've come to love. With a little bit of effort, you can enjoy those colorful blooms on your windowsills all winter long.
The annuals that adapt best to life indoors are actually the tender perennials that those of us in colder climates tend to grow as annuals. These include popular garden annuals such as geraniums, coleus, wax begonias, heliotrope, and impatiens. An added benefit to overwintering these plants indoors is, not only do you get to enjoy their beauty longer, you also can avoid having to buy them again year after year. This is a great way to keep annuals that are special to you, or that have really nice color or fragrance.
To overwinter your annuals indoors, just dig up the entire plant before your first fall frost. Cut the plants back by about a third, and plant them in pots in fresh organic potting soil.
Another way to overwinter annuals is to take cuttings from your existing plants. To do this, take three to five inch cuttings from vigorously-growing plants in mid-summer. If possible, take the cuttings from non-flowering shoots. If you do have to take them from flowering shoots, then just cut or pinch off any blooms or buds when you take the cutting. Remove any leaves from the lower half of each cutting and insert the bottom third of the stem into a pot of moist potting soil. You can add rooting hormone if you like, but most cuttings taken this way will root easily enough without it. Place a plastic bag over the pot (supporting it with a couple of skewers, twigs, or stakes to keep the plastic up off of the plant) and place your pot of cuttings in a bright place, but not in direct sun (you don't want to cook your cuttings!) In about three or four weeks, the cuttings will be rooted, and you can then remove the plastic bag and place the pot in a sunny window.
Selecting Healthy Plants or Cuttings
No matter which method you choose for overwintering, you'll want to make sure you're not bringing additional problems in with your plants. Carefully inspect each plant or cutting for signs of pests or diseases, and avoid bringing in any that show problems. If you really want to overwinter a plant that is showing signs of disease or pests, you'll want to quarantine it well away from the rest of your plants until you are sure you have the problem under control.
Caring for Overwintering Annuals
You'll basically treat your overwintering annuals as you would any houseplant. You'll want to make sure they have plenty of light, water them when the top inch of soil is dry to the touch, and keep an eye on them for any pest or disease problems. They will not need feeding during the winter, but if you like, you can start feeding them in late winter or early spring with a liquid feed such as vermicompost tea.
When it's time to move your overwintered plants back outside, you'll want to make sure you give them time to acclimate to outdoor conditions. You'll want to harden them off, the same way you would with any seedlings you grew indoors. This will ensure that you have a strong, healthy plant to grow in your garden, rather than one that is weak from being tossed into harsh outdoor conditions from its warm, perfect indoor conditions.
That's really all there is to it. So if you have a special annual, or just want to save money so you don't have to keep buying annuals year after year, now you can try overwintering the ones you already have.