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Hortensia (Hydrangea macrophylla)

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Hydrangea macrophylla.
Photo: Jardin botanique de Montréal (Gilles Murray)

Colourful hydrangeas that aren’t very hardy!

Hydrangea macrophylla, or hortensia, is the species most commonly grown as a flowering house plant for Easter and Mother’s Day.

Indoor growing

If you were planning to keep your hortensia indoors, you shouldn’t expect it to survive for long, because it won’t thrive in the heat and dry air. Place it in a cool room, away from any heat source, and keep it well watered. It needs a bright spot, out of direct sunlight. The cooler the temperatures, the longer the blooms will last: under 16°C, about 8 weeks, and less than a month at normal room temperatures. Optimal temperatures are around 18°C in daytime and 15°C at night. During its active growing period, from April to September, it needs a lot of fertilizer. As long as you keep it in its pot indoors, we recommend feeding it every other week with balanced fertilizer (ex: 20-20-20).

Outdoor growing

In our climate, Hydrangea macrophylla is not very hardy. Although the roots can easily survive to zone 5, the stems and flower buds are sensitive to frost (zone 6), especially during cold winters without snow. It needs a spot that is protected from winter winds and where snow accumulates, without melting too quickly in spring (on the east or north side of a foundation). It also needs winter protection.

If you garden in zone 5, why not give it a try at home? Once your hortensia has finished blooming, cut it back, keeping just two pairs of leaves on each stem. Then that same spring, as soon as the ground has warmed up, plant it in your garden in a partially shaded spot. It can tolerate full sun, but avoid any site that is extremely hot. In the year you plant your hortensia, amend the soil with compost and water frequently to help the roots become established. In subsequent years, water only during dry spells and add a layer of compost every year to provide the plant with the necessary nutrients. Mulching keeps the soil moist in summer and protects plant roots during winter.

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