Watering and feeding
Pelargoniums are not thirsty plants so water moderately from spring to summer, taking care that the compost doesn’t become too wet. Open windows or vents in a conservatory or greenhouse in summer to be sure of good air flow. Water only sparingly in winter, so that the compost has time to dry between waterings.
Your pelargoniums will respond well to feeding so apply a balanced liquid fertiliser according to the instructions on the packet, every 10-14 days in spring. Once flowers start to form, switch to a high potassium fertiliser such as tomato feed, feeding fortnightly throughout the rest of summer. Many will continue flowering if kept at 7-10°C (45-50°F), but reduce feeding to once a month in autumn and winter and stop feeding completely if you have dried your plants off in winter (see below).
Overwintering
You can simply grow your pelargoniums as annuals, pulling them out and adding them to the compost heap at the end of the year. But since pelargoniums are perennial plants you might like to save them for another year, especially if you have grown a type or colour you are particularly fond of. To have a go, try one of the methods described below:
Method 1: Overwintering by taking cuttings
This method works well if you have large numbers of plants to overwinter, especially if they are the soft-stemmed pelargoniums such as Zonal types. It is more reliable than keeping them in a semi-dormant state as described in method 3 but takes a little forward planning.
- In late summer, take softwood cuttings (you can discard the old woody plants at the end of the season)
- Once the cuttings have rooted, overwinter them in trays of compost kept on a well-lit indoor windowsill
- Water the trays only sparingly in winter, allowing the compost to dry out between waterings
- Start feeding in late winter, giving a balanced liquid fertiliser every seven to 10 days according to the instructions on the packet
- Pinch out the shoot tips in late winter to encourage bushy growth
- Pot up the rooted cuttings into individual 9cm (3½in) pots in mid-spring
- Harden off and place or plant outside once the risk of frost has passed
Method 2: Overwintering in containers under glass
Opt for this method when you only have a small numbers of plants to overwinter. You can either keep plants in active growth or cut them back to be more dormant, depending on how much space there is in the glasshouse or conservatory (plants with bushy stems and leaves will obviously need more space than those cut back).
- Bring container-grown plants under cover and lift and pot those growing in the soil before the first autumn frosts. Use John Innes No. 1 potting compost. If you do not have enough space to keep the plants at their full size, cut them back to 10cm (4in). This will also discourage soft growth
- Keep the plants in their pots over winter, in a light, airy, frost-free position
- Check those in active growth at least once a week and water if there are signs of drying. Plants which were cut back require barely any water at all until growth resumes in spring. Open windows or vents on mild days in the glasshouse or conservatory to reduce rotting off
- Re-pot into John Innes No. 2 potting or peat-free multipurpose compost in mid-spring
- Harden off and place or plant outside once the risk of frost has passed
Method 3: Overwintering as bare-rooted plants
This method is the least reliable and only suitable for varieties with tough woody stems, but is worth trying if you have large numbers of plants to overwinter.
- Before the first frosts, lift plants from the ground or pot and shake off excess soil or compost from the roots
- Lay the plants in crates or on a bench in a frost-free place to allow the foliage and stems to dry off and then wrap the plants in newspaper or hang them upside down from the shed or garage roof (which must also be frost-free)
- Inspect the plants in early spring. Those which show signs of growth can be kept. First soak their roots in water for a few hours before potting them up and cutting back all stems to about 10cm (4in). Water sparingly and place somewhere warm and bright such as a greenhouse
- Harden off and place or plant outside once the risk of frost has passed