As cold weather arrives over the coming weeks in many parts of the country, it will be time to deconstruct your container plantings and pull annual plants from the garden. But, did you know that it’s easy to save many annual plants from year to year? It’s a great way to save money and keep your green thumb exercised until spring. Overwintering geraniums, coleus, begonias and many other plants we grow as garden annuals is actually quite easy.
Which Annuals Can Be Overwintered?
The first step in successfully overwintering geraniums and other plants is to determine whether or not the plant is a true annual or a perennial that we grow as an annual because it’s frost sensitive.
Some flowers, like cosmos, sunflowers, zinnias and marigolds, are true annuals that complete their entire lifecycle in one season, shedding seeds and dying when winter arrives. These are not plants that you’ll be able to overwinter, but rather, seed-saving is how to preserve them from year to year.
But, there are many plants that we grow as annuals that are actually perennials in warmer climates. If not exposed to a killing frost, these plants will grow and flower for many, many years. Frost-sensitive perennials included in this group are geraniums, coleus, petunias, silver falls, plectranthus, heliotrope, impatiens and lantana, to name just a few. These are the plants which can easily be overwintered.
How to Overwinter Geraniums & Other Frost-sensitive Perennials
There are several ways to overwinter this group of plants. Which method you choose depends on your resources and the conditions of your home.
Method 1: Grow the Plant as a Houseplant
It’s quite easy to overwinter this group of plants indoors as houseplants, as long as you provide them with some basic needs. Dig the plants out of the garden and pot them up into containers using fresh potting soil. Trim the plants back by half and move them into a sunny room. Make sure they’ll receive ample light or they’ll grow very leggy and pale. If you don’t have a bright enough window, hang a fluorescent shop light from hooks in the ceiling above the plants. Your primary goal is not to produce blooms, so you don’t need to purchase any special light bulbs. Just use fluorescent shop tubes. Keep the bulbs about 5 inches above the plant tops and move them up if the plants grow. Leave the lights on for 12-15 hours per day. Of course you could also invest in an official grow light which will also encourage blooms.
Another good tip is to be careful to avoid over watering. Overwintering geraniums, impatiens and other frost-sensitive perennials are very prone to fungal diseases like botrytis if they are watered too often or if the foliage is frequently wet. Be sure the container has good drainage and do not allow water to sit in the saucer beneath.
Pinching the plants back may also be another necessity once or twice during the winter months. In order to keep the plants compact and bushy, use a sharp, clean scissors to remove the terminal two inches from each stem. This will encourage a well-branched plant that is less likely to become leggy and top heavy.
Method 2: Save the Plant Bare-root
Another way of overwintering geraniums and the other plants in this category is to put the plant into a dormant state and keep it “on hold” for the winter months. This is a great technique if you don’t have enough room to host a slew of potted plants on your windowsill for several months.
Start by trimming the plants down drastically, until they’re just 3-4 inches tall. Remove all the leaves left on the plants. Then, dig the plants up and gently shake the soil from their roots. Lay the bare-root plants out on a sheet of newspaper for 8 hours. After that time passes, use a paint brush to gently remove any soil left on the roots. Pack each plant into its own brown paper lunch bag and twist the top of the bag closed. Gently put the bags into a crate or cardboard box, then put the container in a root cellar, unheated attached garage or basement. The ideal temperature for overwintering geraniums and other plants in a bare-root fashion is between 40 and 50 degrees F.
Every six to eight weeks, open the bags and remove the plants. Spray the roots with a mist of water, shake off the excess, and then put the plants right back into the bags and back into storage.
When spring arrives, either pot the plants up and keep them indoors until the danger of frost has passed and it’s safe to move them out into the garden, or wait until there’s no threat of frost, pull them from their bags, and plant them directly into the garden.
Method 3: Overwinter the Plants as Cuttings
One final technique for overwintering geraniums and other frost-sensitive perennials is to take cuttings from the mother plant and root them indoors. It’s an easy process, and it’s a great way to get even more plants for next season.
Start by taking cuttings from the mother plants just before a frost threatens. You’ll need a clean pair of scissors, a few new 4” plastic pots, a bag of sterile potting soil, a container of rooting hormone (available at local garden centers or online) and a handful of clear plastic baggies and twist-ties.
- Fill each pot with damp potting mix and lightly tamp it down.
- Cut off several 2-3” long stem pieces with the scissors. Each cutting should initially contain three or four leaves.
- Carefully remove all but the uppermost leaf.
- Dip the bottom inch of each freshly cut stem into the rooting hormone (it may be a powder, liquid, or gel) and then firmly insert it into a container of potting soil all the way up to the bottom of the remaining leaf’s stem.
- Place one cutting in each pot (start more than you think you’ll need, since some of them may not root).
- Water the soil and allow the pot to drain, then place the entire thing into a plastic baggie with the opening at the top.
- Use a twist-tie to secure the top – this keeps the humidity high and prevents the cutting from drying out until it can form its own roots in a few weeks.
- Place the covered pots on a bright windowsill (but not in direct sunlight) or under grow-lights or fluorescent shop lights placed about 3 inches above the plant tops.
Remove the bag and water the pots when necessary, always allowing them to drain before putting them back into the bag. If the remaining leaf turns yellow or rots off, as is often the case, go ahead and carefully remove it. In about a month you can remove the bag and continue to water as necessary. Allow the cuttings to continue to grow indoors until spring’s arrival when they can be moved out into the garden.