Geranium

Light and exposure

The pelargonium wants full sun. The more it gets, the more it flowers: aim for at least six hours of direct sun a day, a south or west-facing balcony, a window box against a pale wall that reflects the heat. In shade it grows leggy, turns green and flowers poorly.

It is a plant for pots and window boxes above all, which suits us well since it will need to be brought in for the winter. In open ground it works too, but then give it the warmest and sunniest bed, and still take it in before the frosts if you want to keep it.

Watering

Water regularly in summer, but let the surface of the compost dry out a little between waterings. The pelargonium copes better with a slight shortage than with an excess: a permanently waterlogged substrate rots the base. In hot weather a window box may need water every day; in overcast weather, space it out.

Water at the base, not on the flowers or foliage, and empty the saucers after rain. Water standing at the bottom of the pot is enemy number one, especially in late season when the nights turn cool and the compost dries slowly.

Soil and repotting

It needs a free-draining compost, never heavy or waterlogged. A planting compost for geraniums, lightened with a handful of sand or perlite, does the job very well. At the bottom of the pot, a layer of clay pebbles or gravel keeps the roots from sitting in water.

Repot or set out the window boxes as spring arrives, in a container with drainage holes. Do not crowd the plants: a pelargonium given room spreads and flowers more. In a window box, allow one plant every twenty to twenty-five centimetres.

Temperature and humidity

This is the critical point in Belgium. The pelargonium is frost-tender: it already suffers around 3 or 4 degrees and a frost kills it outright. It thrives between 15 and 25 degrees, in the open air, all summer long. Never put it out before mid-May, the late frosts of the ice saints scorch the foliage in a single night.

As for humidity, it prefers dry, well-ventilated air to a stuffy atmosphere. A window box crammed against a wall, poorly ventilated in damp weather, encourages disease. Let the air circulate between the plants and avoid wetting the foliage in the evening.

Pruning and upkeep

Remove faded flowers very regularly, snapping or cutting the flower stem at its base. This simple gesture keeps the flowering going continuously: a pelargonium that is kept clean flowers from May to October, a neglected pelargonium exhausts itself making seed and slows down.

Pinch the young stems at the start of the season to get bushy plants rather than lanky ones. Feed throughout the flowering period: a special fertiliser for flowering plants every eight to fifteen days in full season. Abundant flowering means high demand, a poorly fed pelargonium yellows and flowers less.

Pests and diseases

In our damp climate, two diseases keep coming back. Grey mould, a grey felting on flowers and leaves in mild, stuffy weather, settles on the faded parts left lying around. Pelargonium rust marks the underside of the leaves with small brown powdery rings, especially in a damp late summer. In both cases: ventilate, remove the affected parts, do not wet the foliage.

Excess water remains the real danger. Waterlogged compost rots the collar and the base, and the plant collapses all at once. As for pests, watch out for aphids in spring and the pelargonium caterpillar, the leaf roller, which bores into the buds and hollows out the stems.

Propagation

Stem cuttings in late summer are astonishingly easy, and it is the best way to renew your plants for free. In August, take a non-flowering stem ten centimetres long, remove the lower leaves, let the cut dry for an hour or two, then insert it into a light, barely moist compost. Rooting takes two to three weeks.

You can also sow under warmth in February or March, but it is slow and the young plants only flower late. For most gardeners, the August cutting remains the royal road: it gives plants ready to take off again the following spring.

Toxicity

Barely toxic to humans, with no real danger on contact. It is however toxic to dogs and cats: eating leaves or stems causes vomiting, loss of appetite and lethargy. Keep the pots out of reach of a pet that nibbles.

Month-by-month care calendar

Green Hub tips

• Never put pelargoniums out before mid-May. A single late frost night is enough to scorch all the foliage.
• Bring the pots into a frost-free place in autumn, in a cool, bright room between 5 and 10 degrees, cut back by half and barely watered: they will start again in spring.
• Remove faded flowers without delay, it is the gesture that keeps the flowering going and makes it last from May to October.
• Take cuttings in August to renew your plants for free: a ten-centimetre stem roots in two to three weeks in a light compost.