Sedum plants are known for their strength and ability to survive on dry, sunny roofs. But what if your roof is mostly shaded? Can sedum grow in the shade? In this article, we answer that question and provide tips for a successful sedum roof in shady conditions. Among other things, we cover what sedum is, how much light these succulents need, which sedum species tolerate shade, alternatives for very dark roofs and practical tips for keeping a sedum roof healthy in shade.
What is sedum?
Sedum is a genus of succulents (also called rock plants or succulents) that occur naturally in rocky and dry areas. They are succulents that store water in their fleshy leaves, so they can withstand drought well. Sedum plants are popular for green roofs because they require little maintenance, do not grow tall and tolerate extreme weather conditions well. They form low pads or mats of varying colors (from bright green to reddish) and often bloom with yellow, white or pink flowers in summer. Thanks to their characteristics, sedums can survive on thin substrates with minimal irrigation.
A standard sedum roof usually consists of a lightweight construction with a drainage layer, a thin substrate layer and sedum mats or cuttings on top. Sedum plants root shallowly and require few nutrients. In full sun some species turn red or orange (a sign of drought stress or winter dormancy), while in favorable conditions they remain fresh green. In short, sedum is the ideal plant for extensive green roofs because of its robustness – but what about shade?
Light requirements of sedum species
Like most plants, sedums need need sunlight for photosynthesis, the process by which they convert CO₂ and water into glucose and oxygen. Indeed, many sedums (as succulents) employ a special form of photosynthesis (CAM) in which they take up CO₂ at night and store it as acid (malic acid), and during the day, with the help of sunlight, break down that acid for their growth. Sunlight is thus essential as a source of energy for sedums: without sufficient light, they cannot produce enough nutrients, grow less and do not flower much, if at all.
Most sedum species are sun-loving. They feel fine in full sun – they are used to exposure on rocky slopes and open plains. Too little light, on the other hand, can cause problems. If sedum plants receive insufficient sun structurally, they start to etiolate: they grow elongated in search of light, with thin, pale stems and greater leaf spacing. Such a weakened plant is less vital and may eventually die if the situation does not improve. The characteristic flowering of sedum will also be less abundant or even nonexistent in shade, as flowers now require direct sunlight to develop.
That said, sedum does require less sun than many other plants to survive. They are tough plants that can still live with little light, albeit at a slower rate. They store water and reserves, which allows them to survive even periods of limited sunlight. Sedums can therefore grow in (semi-)shade, but their growth rate and appearance will differ from specimens in full sun. A rule of thumb is that a sedum roof should receive at least a few hours of direct sunlight per day for sustainable results – often about 4 hours of sunlight per day is considered the minimum for sedum plantings. If your roof section gets less than ~2 hours of direct sunlight, then it is actually too dark for a truly successful sedum roof. In that case, it’s better to look at alternatives (see below).
Which sedum species tolerate shade?
Fortunately, not all sedum species are equally sun-hungry. Some sedum species can tolerate shade better and also thrive in places with fewer hours of sunlight. In general, evergreen, light-green species do better in shade than red or variegated species – the latter, on the contrary, discolor due to bright sunlight. From experience and breeding trials, the following sedums appear to perform well on a shaded roof:
- Sedum spurium – also known as fat wall pepper; a groundcover sedum that tolerates reasonable shade.
- Sedum album – white fatwort; it handles semi-shade well and stays low.
- Sedum reflexum (or tripadam) – also still does well in less sun.
- Sedum takesimense – a lesser-known species that also grows in partial shade.
- Sedum forsterianum – tolerates shade quite well according to grower experience.
- Sedum lydium – fine-leaved sedum species that can grow in moderate shade.
- Sedum pachyclados – can survive on a shade roof, but grows slowly.
These species are frequently included in sedum mats for shade applications. Note that they too need some sun; full deep shade all day remains challenging. But sedum mixtures with a higher proportion of the above species will hold up better in an area that gets only half a day of sun, for example.
You also notice the difference in flowering: sedums in a shady spot will flower less and later than the same species in the sun. For example, Sedum spurium can give plenty of pink flowers in the sun, but in the shade, flowers remain sparse or greenish. This is not necessarily a problem – the sedum roof remains a beautiful green cover – but it is something to be aware of. Observe your sedums on your roof: do they remain a healthy green or do they “stretch” very much to the light and turn red due to stress? In the latter case, you may want to take additional measures (see tips below) or introduce additional shade-tolerant plants.
Alternatives to sedum on shaded roofs
Is your roof so sheltered that sedum would do only moderately well? Then you can look at alternative or complementary plantings that can better withstand shade. Some possibilities:
- Mixture with mosses and herbs: Instead of a pure sedum roof, you can choose a green roof mix that includes sedum, mosses, shade-loving herbs and grasses, for example. Mosses thrive in moist shade and can fill open areas where sedum doesn’t grow as much. A sedum-moss roof combines the drought resistance of sedum with the shade tolerance of moss.
- Saxifraga (rock break): These rock plants like a little more shade and moisture. Species such as Saxifraga arendsii (stonebreak) do well on shade roofs and produce beautiful white, pink or red flowers.
- Pansies and ground covers: Shade-loving pansies(Viola odorata, for example) can bring color to a shaded green roof. Ground cover plants such as periwinkle (Vinca) or wild geranium can also take root in a thicker substrate layer and tolerate shade, provided the roof has sufficient bearing capacity for that extra weight.
- Ornamental grasses and ferns: Some low ornamental grasses do well in partial shade, such as Carex montana (mountain sedge) or blue sheep grass(Festuca glauca). On more intensive (thicker) green roofs, you can even apply ferns or hostas for deep shade, although this requires a very different roof structure.
- Sedum ‘Herbstfreude’ (synonym Hylotelephium): This is actually a taller border sedum that can also be used as a plant on green roofs. It likes sun, but tolerates partial shade reasonably well and produces pink flower clusters in the fall. It is not a typical mat-forming sedum, but can be planted in a more intense green roof for extra height and color
- Wild strawberries: Surprisingly, some species of strawberry (such as Fragaria vesca) also grow in shade if there is adequate moisture. They can be a nice addition in a green roof with slightly thicker substrate layer, and provide flowers and fruit as well.
Note: The more diverse plants (other than sedum) you apply, the more the green roof will move toward a semi-intensive roof in terms of maintenance and weight. Always check that your roof structure can handle a heavier substrate layer before creating a diverse planting plan. On pure sedum roofs, the substrate layer usually stays around 6-8 cm (weight about 80-120 kg/m²), but if you want perennials or grasses, you often need >10 cm of substrate and the weight increases.
Finally, if nothing at all wants to grow due to extreme shade (think of a roof that never gets direct daylight, for example sandwiched between tall buildings or constantly under trees): then, unfortunately, a green roof is difficult to make successful. In such cases, it is sometimes advised to have a gravel roof instead of a green roof – this avoids constant costs and maintenance on plants that do not take root anyway. But usually there is íts of light, and with the right approach you can turn even a (partially) shaded roof into a green oasis.
Practical tips for a sedum roof in the shade
Installing a sedum roof in the shade requires just a little more attention. Here are practical tips to make sure your green roof stays healthy:
Use sedum mats or trays specifically suited for partial shade. These usually contain a mix of shade-tolerant sedum species. A pre-grown sedum mat has the advantage that the plants are already firmly rooted and immediately form a dense carpet, giving weeds and moss less of a chance – this is especially beneficial in the shade.
In shade, the roof dries out less quickly, but paradoxically, a slightly thicker substrate layer is recommended (e.g., 8 cm instead of 6 cm). Why? So the sedums have more nutrient buffer and water reserve for those times when the sun does shine and they suddenly need to dry out. In addition, sedums often grow slower in the shade; extra substrate with nutrition helps them stay stronger. Do be mindful of weight on older or weaker roofs.
Make sure excess rainwater can drain easily. Shaded roofs stay wet longer (less water evaporates due to lack of sun). A slight slope or adequate drainage under the green roof is crucial so that puddles do not remain. Standing water can suffocate roots and promote moss growth. Also, check roof drains every year for blockage by leaves or moss.
On shady roofs, leaves can easily remain (from nearby trees) – remove them in the fall so they don’t smother the sedums. Also keep an eye on unwanted seedlings: less sun can cause mosses or shade weeds to appear more quickly. A little moss is no big deal, but if you notice it displacing sedum, it may indicate too much moisture. If you see a lot of moss developing, then the roof may be too damp; remove some of the moss and improve drainage or let the roof air out a little more often.
Sedum normally needs very little water. It evaporates less in shade, so extra watering is rarely necessary. Only during prolonged heat and drought in the summer can watering be wise – especially on a sloping sedum roof in the shade, because water drains away faster there and the plants can still dry out. Lightly fertilize the green roof twice a year (spring and fall) with special sedum fertilizer, even in shaded areas. This keeps the plants strong and resistant to moss and mold.
Can you do anything to reduce shadows? Sometimes you can. For example, pruning back overhanging branches of trees or removing ivy from walls so that a few hours of sunlight still reach the roof. Every extra hour of sunlight helps. Note, of course, that you don’t need a permit or permission for pruning if it involves municipal greenery.
Every roof is different. Don’t hesitate to ask a green roof specialist for advice on planting if your roof has a lot of shade. Experts can recommend a plant mix that suits your situation. Consider sedum mix with mosses, or perhaps partially more intensive planting with ferns and grasses if your roof structure allows it. A specialist can also assess whether the roof might be too dark and suggest alternatives.
Conclusion: Yes, a sedum roof can be done in the shade, albeit with some caveats. Choose the right sedum species and possibly other shade plants, make sure it is properly constructed with adequate drainage and substrate, and do some maintenance from time to time. That way, even a shady roof will get a nice green blanket. Does your roof have little sun and are you unsure of your options? Feel free to contact us for personal advice – even for challenging roofs we come up with a suitable green solution!
I would like to receive free advice
