Gardenia: how to protect it from cold and overwinter it?

Frost-tender bush with an intoxicating fragrance

Renowned for its fragrant flowers, gardenia is a bush that colonises the tropical and subtropical forests of Asia and South Africa. Depending on variety, flowers range from pure white and ivory to cream and bloom between May and September. To bloom, gardenia needs plenty of light; it is a long-day plant. That is, it needs 12 to 13 hours of light per day for flower buds to reach ripeness. Thus, in winter you may see buds forming but they will seldom open.

Gardenia flower

→ For full details, see plant sheet: “Gardenia: planting, maintenance, pruning, watering“

More or less hardy varieties

Certain varieties of Gardenia such as varieties ‘Kleim’s Hardy’ and ‘Crown Jewel’ tolerate temperatures down to -12°C. These can therefore be grown in open ground in the mildest regions. Gardeners in areas with the coldest, wettest winters will need to grow it in a pot. The same applies to less hardy varieties such as Gardenia thunbergia, which cannot tolerate temperatures below -5°C.

The variety ‘Summer Snow’ is the hardiest. Relatively recent, it has the advantage of tolerating down to -15°C. It is even more tolerant of dry air and soil, without depriving us of its heady fragrance from May to July. This bush forms a small rounded clump about 1 m in diameter. Its leaves are dark green, glossy and elongated. The flowers are somewhat less numerous than on other varieties, but slightly larger. Semi-double, they display a pale white that contrasts nicely with the foliage. As with other gardenias, plant it in partial shade, benefiting from morning sun. It will find its place in a heather soil border alongside azaleas and other rhododendrons.

Overwinter a potted Gardenia

When to bring pots indoors?

As soon as first frosts are forecast, that is from mid-October in northern France — the further south you go, the later the date. Pots are particularly vulnerable to frost because of their small surface area. Frost can penetrate across the whole surface that closely surrounds the rootball and roots. They must therefore be brought indoors before these frost events.

Where to keep the pot in winter?

Gardenias grown in pots should be brought indoors for winter. But not just anywhere! Do not place them next to a fireplace. Ideally install them in a greenhouse or conservatory. If you do not have either, choose a room with a temperature of around 17°C, an ideal atmosphere for gardenia. It can tolerate up to 24°C, but will then need more humidity. Avoid locations with draughts and favour a bright spot without direct sun. For the pot, opt for terracotta to allow moisture and air to pass.

Gardenia in a pot

Winter care for potted gardenia

Gardenia does not require much maintenance if well placed. Gardenia loves humidity. It is recommended to place it on a tray of clay pebbles or pebbles soaked in water. This allows the plant to benefit from evaporating water. In addition, it is regularly watered and bathed during the growing season, provided the flowers are not wetted. In winter, limit watering to twice a month. In any case, never water with hard (calcareous) water — gardenia hates it! Prefer rainwater. Always wait for the growing medium to dry before watering again; this bush likes humidity but not to be waterlogged. The tray of pebbles or clay pebbles should be kept with a few centimetres of water at all times to provide constant humidity.

Protecting gardenias planted in the ground

A few very simple steps help Gardenia withstand winter chill. Even if you live in a mild area, better to be cautious and give these few care measures to this bush.

Here are some steps that will help it get through winter in the garden :

1. Start by placing it in a spot sheltered from wind, ideally against a wall. Winter sun will then warm the plant.
2. Then, give it a layer of mulch before winter. Choose pine bark or leaves, which will keep roots warm and acidify soil at the same time.
3. To protect it from frost, cover it with a winter fleece, which will also protect it from rain, snow or even thin hail. Air regularly on days when there is no frost: lift the fleece for a few hours, taking care to replace it at night. Put the fleece in place as soon as first frosts are forecast.
4. For watering, reduce to once a week, preferably in the morning, so it does not freeze overnight.