In internet forums and also in some gardening guides it is repeatedly claimed that olives can overwinter outdoors even without protection. This statement is simply wrong, because olives are Mediterranean plants and cannot tolerate (long-term) frost.
When and how should you use a heater for olive trees?
An olive tree heater should only be used in very cold winters with prolonged frost periods to protect the roots, trunk and crown from the cold. Ensure even, moderate heat distribution and use alternative methods of protection such as wraps.
Overwintering olives properly
Short-term frost does not harm older olive trees in particular; they often know this from their homeland. However, long-lasting and deep frosts cause the tree to die. Olives kept in pots and young trees in particular should therefore be comprehensively protected if they are to overwinter outdoors. It's best to place these in a bright but not too warm place - temperatures from just above freezing to around 10 °C are ideal for the resting phase. But even time-honored solitaires cannot survive the winter without the appropriate protection.
How useful are heaters?
Experienced gardeners will advise you to equip outdoor olives in winter not only with a thermal protective cover, but also with heating for the roots and trunk. In winter, the roots are particularly at risk because if they freeze due to prolonged ground frost, the entire tree will die. However, if they are retained, the olive will usually sprout again. Special root heating systems make perfect sense, as they protect the most sensitive parts of the olive from the cold. There are special plant heaters for the roots, the trunk and also for the crown.
When plant heaters should be used
- Plant heaters are only necessary in very cold winters with prolonged periods of frost
- at temperatures around freezing point or just below, wrappings are sufficient
- make sure that the entire tree is heated evenly so that there is no temperature gradient (e.g. between heated roots and cold crown)
- also heat the sides evenly
What speaks against plant heating
But be careful: Plant heaters don't just have advantages, which is why they should actually only be used when temperatures are really deep and/or persistently below zero. Olives enter the vegetative phase at temperatures above around five degrees Celsius, which in turn can lead to drying out in the dead of winter. Therefore, plant heaters should never be set too warm, as this disturbs the plant during its winter rest phase. The warmth also attracts eating pests such as mice, but fungi and scale insects also feel very comfortable on heated plants. In addition, many heaters have the problem that they only heat on one side and some parts of the plant remain unheated. In such a case, warming wraps are the better choice as they provide even heat.
Tips & Tricks
Wrap your olive with a standard outdoor fairy light (€17.00 on Amazon), then wrap the trunk and crown with a thick fleece material. You can cover the roots with a thick layer of bark mulch (at least 25 centimeters!) and with foil to protect against moisture.