Breathtaking and colourful early spring flowers on your rooftop are also possible with flower bulbs. By using small bulbs—often classified as naturalising bulbs—you can enjoy colourful rooftop greenery for years to come.
Green roofs is a broad term. Depending on the type of green application on the roof, there are various possibilities (or limitations) for using flower bulbs.
Green roof with minimal substrate and/or substrate substitute layer
The bulbs suitable for these roofs are small in size but generally need at least 8 cm of substrate to grow and develop properly. After planting, ensure they receive enough water to build a strong root system before winter. To create a rich and long-lasting display of colour in spring, it’s best to use a mix of bulbs with different flowering periods. Be sure to plant enough—around 100 bulbs per m² of roof is recommended.
Planting is easy: make a hole in the vegetation (through the mat or between plants) using your hand or a round stick. Place the bulb into the hole and firmly press the surrounding substrate or ground cover back into place. Always plant the bulbs as close as possible to the base of the green roof—right up to the drainage layer or trays.
If the roof build-up includes a substrate substitute, it’s important to note that bulbs cannot be planted directly into or onto this material. Make sure there is a minimum 3 cm layer of substrate between the substitute and the bulb.
If the green roof construction contains no substrate at all, unfortunately, it is not possible to use flower bulbs.
No additional maintenance is needed. Once the bulbs have finished flowering, they retreat naturally: the leaves wither and dry up.
Bulbs for green roofs (minimal substrate layer)
Different bulbs prefer different substrate depths. From 6 cm, you can use crocuses, small daffodils like ‘Tête-à-Tête’ (with smaller bulbs), glory-of-the-snow (Chionodoxa), Ipheion, and Puschkinia. From 8 cm and up, the substrate is suitable for snowdrops, Iris reticulata, Scilla siberica, and wild tulips. Grape hyacinths (Muscari) prefer a thicker layer to return year after year—they develop a large root system that requires substantial substrate. If the roots dry out too quickly, the offspring will struggle to grow properly.
Even at high altitudes, naturalising bulbs contribute to biodiversity.
Rooftop gardens
More and more rooftops—especially on tall buildings—are being transformed into lush gardens. Rooftop planting helps regulate heat (particularly in urban areas) and improves water retention. Moreover, green roofs offer a fantastic opportunity to support biodiversity.
Where complete gardens are created with perennials, shrubs, and even trees, it is certainly also possible to plant flower bulbs. The substrate layer is generally thick enough for almost any flower bulb from the Verver Export catalogue to thrive!
It’s important that rainwater is properly absorbed by the vegetation and doesn’t remain trapped in the substrate, as bulbs in their dormant summer or autumn phases can rot under prolonged moisture. On the other hand, drought in summer may also threaten certain bulbs. Many daffodils, for example, require a slightly moist soil during summer months, which might not always be the case on rooftop gardens. For best results, plant daffodils in areas with some shade throughout the day to reduce substrate evaporation.
Ask our regional experts (www.ververexport.com) for tailored bulb advice for your high-altitude projects!
