Learning how to overwinter geraniums is really handy for a gardener to know as it can save money and allows you to prolong the life of varieties you are particularly fond of.
Geraniums, or pelargoniums, are stalwarts of the summer garden. Available in an array of colors, and flowering continuously provided they are deadheaded, geraniums are perfect for bringing cheer and long-lasting color to hanging baskets, containers and borders.
However, they should be one of the winter garden ideas you have in mind when compiling your job list.
Planning a winter garden is vitally important when it comes to frost-sensitive plants. While they put on a long display and are perennial plants, geraniums are frost tender, meaning that they will not survive harsh winters – so knowing how to overwinter geraniums is a must if you are keen on growing them.
Originating from South Africa, geraniums are happiest in the heat, and can tolerate periods drought with little water.
Geraniums, or pelargoniums, are hardy in USDA zones 9-12 in climates of between 20ºF to 50ºF and can survive to zone 7 to temperatures of -12ºF (0ºC) if protected. While they can survive light frosts (temperatures just below freezing), they will die if exposed to prolonged temperatures below freezing so need to be protected in these conditions.
‘The Pelargonium group is very diverse and has many growing forms all of which are classed as tender perennials. This means that they are not frost hardy as the majority of the originating species come from the warmer climbs of the Southern Hemisphere,’ says David Taylor, Vice Chairman of the UK Pelargonium and Geranium Society.
‘Being perennial means that they can continue to grow for a number of years but in the UK this would mean that they would need to be protected from, not only frost, but also winter wet and damp.’
You can treat geraniums like annuals, digging up the plants in fall and composting them and replacing them with new plants the following year. However, given the right care and treatment, you can winterize geraniums, keeping them alive over winter ready to flourish again the following year.
‘Keen enthusiasts keep their pelargoniums in growth during the winter and continue to feed and water but a few key points can be undertaken by anyone to keep your pelargoniums (geraniums) alive throughout the winter,’ explains David Taylor, Vice Chairman of the UK Pelargonium and Geranium Society (opens in new tab).
Geraniums are the common name for pelargoniums and should not be confused with hardy geraniums or cranesbill which are a different type of plant and do not require overwintering.
How to overwinter geraniums
There are different ways to overwinter geraniums. Potted and kept in the right conditions, the plants can be kept either growing or in a semi-dormant state over the winter, however they can also be overwintered in a dormant state and stored in bare-root form. Below we outline the two separate methods with help from the experts. Another alternative is to take cuttings from your geraniums to create new plants for the following year.
How to overwinter geraniums in pots
Often geraniums are grown in containers, and this is a great way to grow them if you are looking to overwinter them.
Move pots under cover
If your geraniums are already in pots, in fall, before the frost arrives, these pots can simply be moved under cover into a light, airy and frost-free place such as a greenhouse or conservatory.
‘The best place would be a greenhouse and the ideal environment would be to have a heater in place to maintain temperatures above freezing when frost does threaten,’ says David Taylor, Vice Chairman of the UK Pelargonium and Geranium Society. (opens in new tab) (PAGS).
If your geraniums have been grown in a border, you can dig these up, repot them and bring these pots undercover, too.
Cut plants back
Whether they are already potted or have been taken from the border and repotted, it is best to cut geraniums back before bringing them inside, as David Taylor of PAGS explains.
‘Firstly you should cut your plants back by about two thirds; if lifting from outdoor beds they may need to be cut down by three quarters or even more and only do this cutting when the roots are dry otherwise the remaining stems will die back.’
‘Also, remove any dead, damaged, and unhealthy areas you see. Make sure they are free from bugs, and then bring them in for the winter,’ adds Emily Fernandes, a small space gardener from California and a consultant at HouseGrail (opens in new tab).
Whilst under cover the geraniums are best kept in a semi-dormant state and so will not require feeding and will need less watering. ‘Put them in an area that gets partial sun and water them every 2-3 weeks, keeping them at around 50% humidity. Like most other plants, they go dormant through the winter to preserve their energy for the growing season,’ adds Emily Fernandes, consultant at HouseGrail (opens in new tab).
Can I overwinter geraniums in an unheated greenhouse?
Whilst a heated greenhouse is preferable, ideally set to a minimum of 46ºF (8ºC), you can overwinter potted geraniums in an unheated greenhouse, if doing this, ‘keep it well insulated with bubble wrap or the like and cover plants with fleece when very cold weather threatens,’ advises David Taylor of thepags.org (opens in new tab).
If you don’t have a greenhouse that geraniums can be kept in a conservatory, ‘but the preference would be one that is unheated as if it is too warm you may get a lot of lanky growth due to the low light levels in the winter,’ adds David.
If you do not have a greenhouse or conservatory smaller pots can be bought inside the house and placed on a sunny windowsill.
If you have potted geraniums too large to be brought inside you can consider leaving them outside says David Taylor.
'If you have really large potted pelargoniums outside and have a south facing wall you can chance putting the pots up against this for the winter. However, in this case, you should not cut the plants back as the growth will offer some protection to the roots during periods of very cold weather,' he explains. 'Should we have a very cold winter it is unlikely that plants in this position would survive.'
How to overwinterize geraniums in bare-root form
Geraniums can also be overwintered in bare-root form (with no soil around the roots) and stored in a dormant state ready for repotting in spring. This method will take up less space in comparison to overwintering geraniums in pots and is the best way to store large numbers of geraniums. This method does not require a greenhouse, they can be stored in a shed or garage.
Dig them up If using this method, before fall, dig them up and shake off all the soil from the roots and let them dry out for a couple of days.
Cut back At this stage cut back the stems to around 4 inches (10cm), trim the roots to about 5cm and remove any leaves.
Store The nest step is to ‘place them in a cool dry area in paper bags or cardboard boxes. We cover our plants with seasoned sawdust,’ explains is to Tammy Sons, CEO at Tn Nursery (opens in new tab) near Nashville Tennessee. You can also wrap them in newspaper or cover them with potting compost.
Pot up In early spring the bare-root plants that show signs of growth can then be potted up, but it’s recommended to soak the root for a few hours before doing so.
Cut back Once potted up, the plant should be cut back. ‘It’s necessary to cut back your geranium plants when you unpack them in the spring,’ advises Bryan Mackenzie, landscape designer and co-founder of bumpercroptimes.com (opens in new tab). ‘You have to cut all the stems back to healthy-looking green growth. It’s also a good idea to trim off all the roots that are significantly longer than the others,’ he adds. This is different to deadheading geraniums in summer to promote more blooms.
Harden off The pots can then be placed in a sunny, frost-free spot to kick start growth and gradually hardened off after the risk of frost has passed before being finally brought outside into the garden ready for its summer display.
When should you overwinter geraniums
Geraniums are tender perennials so will need protection from hard frosts by being brought under cover, it is important that this is done in fall before the winter frosts set in.
What is the best way to overwinter geraniums?
The best way to overwinter geraniums will depend on how many plants you want to overwinter and the overwintering space you have available. Generally it is easiest to keep them in pots and to move them into a light, airy and fros- free space such as a greenhouse or conservatory. However, if you want to overwinter lots of geraniums it may be better to store them in bar- root form within paper bags and kept in a cool, dry place.