Overwintering geraniums can be done in one of two ways - keep them growing in containers or prepare them for dormant storage.
OVERWINTERING IN CONTAINERS
If your geraniums are already in smaller, more manageable containers, you can bring the container in before the first frost. Apply a systemic insecticide a week ahead of time to prevent bring bugs indoors with your plants. When you are ready to bring the geraniums inside, cut them back by half and remove any dying or damaged foliage. Examine the plant and if it is healthy looking, bring it indoors.
If your geraniums are planted in the ground or in large, unwieldy containers, prepare a container to transplant your geraniums in. Add potting soil and do NOT use garden soil. Garden soil is too compact and does not drain well in a container. Potting soil is more porous and allows for drainage with room for root development.
Cut your geraniums for transplanting back by half and inspect them to ensure their healthiness. Then transplant them into your prepared container. Water well.
Whether you bring a container in or prepare a new container, you will want to find a place in your home that is cool and has plenty of direct sunlight. Water your plants as needed to prevent the soil from drying out. You can pinch back the tips of the stems to prevent your geraniums from becoming leggy which generally weakens them. Pinching will also encourage more branching which makes for a fuller plant. You will most likely not have to pinch your plants back more than once or twice during the winter.
When spring rolls around, give your geraniums a light application of fertilizer before planting or taking them outside. This can be done in early May. Once the plants are outdoors again, fertilize them weekly with a liquid fertilizer such as Miracle-Grow to keep them blooming their best. Follow fertilizer instructions carefully and do not over-fertilize. If you get plenty of lush green foliage but no blooms, cut back on the fertilizer!
PREPARING FOR DORMANT STORAGE
Geraniums may also be stored and allowed to go dormant through the winter months. Because geraniums have very thick stems, unlike most other annuals, they can survive well without soil if they are correctly prepared and stored.
Dig up the entire plant before they have been exposed to frost. Shake loose any soil from around the root. Shake gently so you don’t damage the roots. Place the plants into brown paper bags which will be stored open or hang them upside down from rafters or clothes hangers. When tying them up, use soft cotton strips or another material that will not cut into the stems when tied loosely around them. Suspend the plant so it hangs upside down.
Whether in bags or hanging, you will want to place your geraniums in a cool, dark place. Ideal temperatures for storing geraniums in this fashion run between 45-50 degrees Fahrenheit.
Once a month inspect your plants. Many, if not all the leaves will dry up and drop from your plants through the course of the winter. This is normal. The stems should stay firm and solid! If any stems are weak you should discard them as they probably will not survive to grow healthy plants. After inspecting your plants, soak their roots in water for 1-2 hours before returning them to their storage location.
In late March or early April, start potting up your dormant geranium roots. Use a good potting soil and water them well after potting. Place them in a sunny location to get new growth started. Cut off any dead stem tips. Turn your pots regularly to encourage even growth. Your geraniums may be planted outside after danger of frost has passed.
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