An oleander full of flowers, a little lemon tree with real fruit, an olive in a terracotta pot: Mediterranean container plants bring holiday mood to terrace and balcony. But with the first frost the end threatens, for few are hardy. Whoever wants to bring them through winter must bring them in on time and overwinter them correctly.
The most common mistake is well-meant: you bring the plants into the warm living room, where they grow leggy in the dark, lose leaves and get pests. The key lies elsewhere, namely in the cool, bright quarters and in sorting by frost hardiness. This article shows you which plant needs which quarters and how it comes through winter healthy.
Sort by frost hardiness
Not every container plant needs the same winter quarters. The first and most important step is therefore to sort your plants by their cold tolerance. Roughly there are three groups, and each wants to be treated differently.
The three frost groups of container plants
- Almost hardy: cool, tolerates light frost
Olive, potted fig, bay and some palms tolerate a few degrees below zero. They overwinter cool and bright, in mild regions with protection even outdoors on the house wall.
- Frost-sensitive: bright and frost-free
Oleander, citrus, olive in a rough climate and many Mediterranean classics want a bright, frost-free room at about five to ten degrees. Short, light frosts the oleander still shrugs off, permanent frost not.
- Sensitive: warm or fully dormant
Angel's trumpet, hibiscus and lantana are especially cold-sensitive. They need a frost-free, often slightly warmer quarters or are cut back hard and stored dark.
- Evergreen versus deciduous
Evergreens like citrus and oleander need light in winter. Deciduous ones like fig and angel's trumpet may stand darker and cooler, because without leaves they need no light.
As a rule of thumb for most Mediterranean container plants: as cool as possible, as bright as necessary, always frost-free. An unheated, bright conservatory, a stairwell, a frost-free garage with a window or a cool cellar room with light are ideal. The cooler the plant stands, the less light it needs, because its metabolism slows down.
Why cool is better than warm
The thinking error in overwintering is wanting to make it cosy for the plant. Yet the warm home is almost the worst quarters for Mediterranean container plants. In room warmth their life processes continue, they sprout and need much light for it, which they lack in the dark winter. The result is long, pale, weak shoots, dropping leaves and easy prey for pests like scale and mealybugs.
Cool-overwintered plants, by contrast, fall into a kind of rest phase. Their metabolism slows down, they need hardly any water, little light and no nutrients. That way they come through winter strong and healthy and start into spring full of strength. The ideal temperature for most is about five to ten degrees.
The principle resembles that with Mediterranean herbs and other potted plants. Whoever has several sensitive plants best sets up a fixed, bright, cool winter quarters in which they all overwinter together.
The root ball is the weak point
As with all potted plants, the root ball is the most vulnerable spot with Mediterranean container plants too. In the winter quarters two dangers threaten: freezing through and rot. Both affect the roots first.
If the plant stands in a room only just frost-free or is to stay outside with protection, you insulate the pot against cold from below and wrap it if needed. The greater danger in the quarters, however, is often the wet. In the rest phase the plant uses hardly any water, a too moist ball then rots easily. So the rule is: water clearly less in winter, keep the soil only slightly moist and absolutely avoid waterlogging. Empty saucers after watering.
Bringing in and out at the right time
The timing matters too. Bring the plants in before the first frost comes, mostly from weeks 40 to 44. But do not wait too long: a cold night frost can catch sensitive species like the angel's trumpet overnight. Conversely the plants should not come in too early, for a few cool autumn days outdoors harden them off.
Bring in before the first frost
From late September keep an eye on the weather forecast and bring the most sensitive plants in first. Robust ones may stay outdoors until frost is announced.
Check for pests
Look each plant over carefully before bringing it in. Dragging pests into the quarters backfires, because they multiply strongly in the warm confinement. Remove infested leaves.
Water little, do not feed
Stop feeding entirely in winter and water only so much that the ball does not dry out. The plant rests and needs almost nothing.
Put out again slowly
After the Ice Saints in mid-May the plants may go back outside. Get them used to the sun slowly, first to a shady spot, otherwise there is sunburn on the leaves.
Sort by frost hardiness, cool and bright rather than warm and dark, protect the root ball and water little. That way oleander, citrus and co. come through winter healthy.
The core rule for overwintering
Frequently asked questions
How do you overwinter container plants correctly?
Most Mediterranean container plants overwinter cool and bright at about five to ten degrees, always frost-free. A warm room is unsuitable, because the plants grow leggy in the dark there. In winter you water only little and do not feed at all.
Which container plants are hardy?
Few are fully hardy. Olive, fig and bay tolerate some frost and overwinter outdoors in mild locations with protection. Oleander and citrus tolerate only short, light frost and want a bright, frost-free quarters. Angel's trumpet and hibiscus are sensitive.
Why does my container plant lose its leaves in winter?
Usually it stands too warm and too dark. In a warm room the plant keeps growing but does not find enough light and sheds leaves out of need. Put it cooler and brighter, then it falls into the rest phase and keeps its foliage.
When do you bring container plants in?
Before the first frost, mostly weeks 40 to 44. Sensitive species like the angel's trumpet first, robust ones like the olive last. Put out only after the Ice Saints in mid-May, then get them used to the sun slowly.
How much do you water container plants in winter?
Very little. In the rest phase the plant uses hardly any water, a too wet root ball rots easily. Keep the soil only slightly moist and empty saucers after watering. Waterlogging is the greatest danger in winter.
