Method 1
The easiest way to overwinter geraniums is to simply uproot them from the garden before the first heavy frost in the fall. Cut them back quite severely and pack them closely together in deep boxes, covering the roots with fresh potting soil and peat moss. Place them in a dimly-lit storage area or basement where the temperature is approximately 4-7ºC. (40-45ºF.). Water the soil lightly initially and then, throughout the winter, sufficiently to keep the soil from drying out completely. Early in April pot up the surviving plants in individual pots. Water well and place in a brightly lit area. Rapid growth will be evident and by planting time in May, good well-branched plants should have developed.
Method 2
Plants can be dug up from the garden and potted up. Trim back the plant by one third to reduce transplant shock. Use light potting soil and liquid transplant fertilizer. Keep the plants in a sunny location for the winter. The plants will continue to grow and sometimes flower during the winter. In the spring, cut back the weak growth to promote bushiness. Place plants out, once the chance of frost has passed.
Method 3
Dig up mature plants and remove all soil from the roots. Dust with a fungicide and insecticide powder. Store the plants in the basement or cold room by hanging them from a rafter. Keep them cool and dark during the winter. In late March or April bring the plants down. Prune them back by one half and pot up in a light potting mix. Fertilize with transplant fertilizer to stimulate new roots. Begin watering and fertilizing on a regular schedule. Keep them in a sunny location. Transplant into the garden after any chance of frost has passed.
Method 4
If a cold cellar is not available, then cuttings are another option. These are best taken from late August through to September. Select short tip shoots, approximately 4 in. in length, cutting beneath a leaf node. Remove the lower leaves allowing the top two pairs to remain and allow the cuttings to dry for several hours. Dip cuttings in a rooting hormone powder, shaking off excess and plant in a rooting medium. Provide a clear plastic cover for two to three days to promote humidity but do not allow this to remain if condensation builds up. Place in a bright light out of direct sunlight until roots have formed. Discard any cuttings that rot or appear to be diseased. As they grow the cuttings can be potted on into individual, larger size containers and then transferred outside once frosts have passed. Pinch out as necessary to produce a good bushy plant.
