You’ll often hear said about clematis (Clematis spp.) that they like having their head in the sun and their feet in the shade. That isn’t quite true, though. They really don’t mind if if their roots are exposed to sun per se. What they don’t like is dry soil, nor do they appreciate extreme heat. And logically speaking, soil constantly exposed to blazing sun will likely dry out faster and be hotter than soil that is shaded. If the soil in your garden is naturally moist, or if you water when the soil starts to dry out, it will keep your clematis roots both well watered and fairly cool and, under those circumstances, you can certainly grow clematis with their root zone in full sun.
Still, in many if not most circumstances, it is worthwhile providing some shade for the roots. One can for example follow the most common recommendation for clematis care and plant annuals, perennials, small shrubs or other plants with dense foliage so they cover the root zone. However, these plants will also want their share of the soil’s moisture and will also compete for nutrients. That’s why it is often even easier just to mulch the ground at base of your clematis.
In fact, if ever there is a plant that loves mulch, it’s clematis. First, under a mulch, the soil is always cooler, to the delight of your clematis during spells of brutally hot weather. Moreover, since it prefers soil that is always slightly moist but never soggy, mulch, with its ability to reduce evaporation in dry weather, yet to act like a sponge and absorb excess moisture in damp weather, gives you just the helping hand you need. Last but not the least, the roots of clematis are fragile and dislike disturbance… and using mulch eliminates weeds and therefore the need to cultivate, thus leaving the root system undisturbed.
Cover the ground at the foot of your clematis with 2 to 3 inches (5 to 7 cm) of shredded leaves, rameal chipped wood, forest mulch or some other rich mulch and you’ll see: your clematis will be more vigorous than ever! However, avoid “red cedar mulch” (actually arborvitae chips stained orange). This mulch is slightly toxic to most plants and therefore not suitable for delicate plants like clematis.