in the UK
Given correct cultivation (click for advice on cultivation in the UK) and siting, the majority of cistus and halimiums are perfectly hardy in the UK and will only be harmed by exceptionally wet and cold winters. My collection is in the north of England at an elevation of 200 metres (660 feet). Most kinds thrive outdoors here because I ensure good drainage.
They are susceptible to physical damage from heavy snowfalls, which may crush or split their brittle branches. Prolonged snow cover is particularly harmful to felted-leaved kinds, such as C. albidus and some of its hybrids.
If at all possible buy plants raised in soil-based compost. Unfortunately it has to be recognised that commercial growers now use exclusively compost based on peat, coir or other organic materials and will not accept the increased costs of using a tailor-made compost for cistus. It is worth seeking out a specialist nursery that uses a gritty, soil-based compost.
The problems with peat compost are serious. Such an organic medium is the antithesis of their native habitats. If over-enriched it produces lush, tender growth ill-prepared to face the winter; it may shrink and dry out after planting in summer, then get waterlogged in winter, drowning the roots; it may not be sufficiently firm to prevent wind-rock, to which these plants are very susceptible. If you have to buy plants in peat compost, do everything possible to improve the drainage of the planting site and take cuttings immediately as an insurance against the possible loss of your plant in the first winter. Do not assume your plant died from cold. Excess moisture is a far more likely killer.
There are a number of cistus which can be recommended as absolutely hardy and immune to frost damage (1) and many others which need only to be sited in a position with a little shelter from the coldest winds (2):
(1) The hardiest
Cistus laurifolius, C. ‘Grayswood Pink’, C. x cyprius, C. x laxus (including ‘Snow White’), C. ‘Snow Fire’, C. x ledon, C. x oblongifolius, C. x platysepalus, C. ‘Ann Baker’, C. ‘Jessamy’ series, C. sintenisii; also x Halimiocistus ‘Ingwersenii’ and x Halimiocistus sahucii, which are ideal for a large rockery.
(2) Very unlikely to suffer frost damage
C. x aguilarii, C. ladanifer (most kinds), C. x canescens, C. x hybridus, C. x dansereaui ‘Jenkyn Place’, C. x dansereaui ‘Portmeirion’, C. x florentinus, C. monspeliensis, C. x obtusifolius, C. x argenteus (including ‘Peggy Sammons’, ‘Silver Pink’, ‘Stripey’, etc.), C. x pulverulentus, C. x crispatus, C. x nigricans, C. x platysepalus, C. populifolius, C. x verguinii f. albiflorus, C. x stenophyllus, C. ‘Ruby Cluster’, C. ‘Gordon Cooper’, C. ‘Christopher Gable’, C. ‘Little Gem’, C. x dubius, C. x bornetianus ‘Jester’,
Halimium lasianthum, H. umbellatum, H. x pauanum,
All the rest will survive the average winter with a little more shelter, except the following (3), which are not reliably hardy and can be expected to survive milder winters only in the warmer areas of the country if sited in a sheltered position, e.g. against a south-facing wall.
(3) Not hardy
C. parviflorus, C. ochreatus, C. symphytifolius, C. osbeckiifolius, C. chinamadensis, C. munbyi,
NB. Any kinds not specifically mentioned in (1, 2 & 3) above should be assumed to be hardy enough to survive an average winter in a warm, sheltered position, but may be damaged or killed in a severe winter.