The recent cold conditions have highlighted the difference between warmer coastal areas of the Algarve and the inland hills.
Although air frosts are rare, a drop in temperature or slightly below freezing separates the hardy from the tropical succulents that many of us grow in our gardens. In general, succulents are cold-hardy but not frost-tolerant, and can survive temperatures to 1.0ºC.
It is only when we have experienced these rare cold and frosty conditions that we find out which succulents are truly hardy. Cold also has some interesting effects on most succulents. The best and brightest colours start showing when temperatures fall below 10ºC. The chill stresses succulents, so they start growing a little more compact and colourful.
The recent trend for using succulents as fire-resistant and drought-tolerant planting has increased interest in exploring the range of their colours and forms, with foliage and flowers providing contrast and colour in the garden.
Even within a relatively small area, placing vulnerable plants where cold air does not settle can make the difference between life and death.
Low lying or damper areas should be avoided for tropical species in much the same way as for tender perennials such as plectranthus, salvia and pelargoniums.
The key to survival, as with so many mediterranean plants, is good drainage. Try planting into clay soil that is mounded to improve drainage – note when and where damage occurs during cold weather and choose hardy succulents for any new planting.
As usual, knowledge of the conditions where plants naturally occur gives valuable information for cultivation in our own gardens. Succulents from winter-rainfall high-altitude zones will tolerate a wider temperature range.
Unfortunately, the arrival of the agave weevil has removed this family from the plants available for gardens here, but there are many others, and some suggestions for your cold hardy garden are listed here.
Dasylirion texanum is a very hardy plant that inhabits volcanic rock cliffs in mountainous areas in Mexico. It is a member of the Agavaceae family and, therefore, could be vulnerable to the agave weevil, so put new plants in containers to check for infestations before planting out in the garden.
Delospermas serve gardeners well. Originally from South Africa, they are hardy and tough, drought-resistant carpets of evergreen foliage with a range of colourful flowers. Often seen in the Algarve hanging down from high stone walls with bright pink flowers is D. cooperi, easily propagated from cuttings.
The Euphorbia family has useful species that look good planted in full sun and need no protection from the frost. Euphorbia tirucalli ‘Fire Sticks’ is a plant that reacts to cold stress by showing pinks and vibrant, red stem colours.
Euphorbia resinifera is a tight, clumping plant with stout, erect stems and also one of the oldest documented medicinal plants.
Euphorbia rigida is a spreading plant and reseeds but not invasively. This leafy perennial produces new stems just as the old flower stems start to fade, when they can be removed.
Euphorbia antisyphilitica spreads by rhizomes to create a vertical accent and looks good with rocks or in a container. Wax from the stem is used in many products such as chewing gum, lip balm and skin creams. Even better, all euphorbias are rabbit proof!
Hesperaloe parviflora has striking coral-red flower spikes as high as 2m emerging from basal rosettes. Native to the Chihuahuan Desert of west Texas, and north-eastern Mexico.
Lesser known is Orostachys, a group of small, low-growing ground cover related to sedum and sempervivum. These are ideally suited for shady situations and come from Japan and northern Asia. O. fimbriata is a desirable steely blue.
Sedum and sempervivum are the main varieties which can handle cold winters, frost, rainstorms (if given excellent drainage) and summer dry spells. There are two sedum commonly available – Sedum spurium (with colourful foliage) and Sedum reflexum (blue foliage).
Sempervivum (Hens & Chicks) has many colourful forms of the Sempervivum heuffelii species which is a tough ground cover. These have a range of bronze, blue-green and pink-edged foliage and, in common with many succulents, they are easy to propagate from the foliage rosettes.
There is also the native Sedum sediforme, which is commonly seen growing on top of stone walls, the best form of drainage!
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By Rosie Peddle
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