Q. Should I bring my potted Martha Washington geranium plant into the house for the winter? Is this type of geranium treated in the same way as zonal geraniums?
A. Both zonal and Martha Washington geraniums are frost-tender Pelargoniums, but they are very different in their preferred growing conditions. Zonals do best in warmth and in soil that remains on the dry side. Martha Washingtons (Pelargonium domesticum, Regal geranium) need cool temperatures to thrive and bloom well.
In late spring, Martha Washington geraniums are popular gift plants. They are impressive — compact, thickly bushy plants bearing ornamental leaves with finely fringed edges and clusters of large, showy flowers beautifully veined and splashed in vividly contrasting colours.
The bloom period can be long if the plant is placed in a cool, lightly shaded spot outdoors as the weather warms. Martha Washingtons often take a break from flowering in the high heat of summer — just as the zonals are hitting their peak of bloom.
Martha Washingtons also winter best in cool temperatures, with only enough water to keep them alive. Temperatures in the 10 to 15 C range, together with bright light and a dryish soil, contribute to successful wintering and help at the same time to set these lovely plants up for really good flowering in spring.
Q. I’ve brought my potted zonal geraniums into shelter and am about to take cuttings from them. Should I place a plastic cover over the potted cuttings to maintain high levels of humidity around them while they are rooting?
A. Plastic “humidity tents” over, but not touching, cuttings, while they root, are generally helpful, but not for zonal geranium (Pelargonium hortorum, P. zonale) cuttings, which are sensitive to damp conditions. High humidity levels foster rotting of the cuttings at the soil line. It’s a condition called “black rot.”
Zonal geraniums root very easily in warmth, bright indirect light, and a porous, that is free-draining planting mix kept just modestly moist.
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