In the wide and varied world of roof vegetation, there are a variety of different professionals who may end up in charge of planting. Extensive green roofs are quite often planted by specialist green roof professionals, but more intensive roof gardens might be undertaken by either a green roofer or a landscaper.
In any case, if the installer is either unused to handling larger plants or unused to planting on roofs, there are a three common pitfalls that can be easily avoided.
- Check the substrate. Even though intensive gardens may use a slightly different substrate from the 80% aggregate extensive green roof substrates, they will generally require a much more free draining engineered substrate than the normal topsoil products used in gardening. Using these will avoid drainage issues and support the plants correctly in the harsh rooftop environment.
- Check the depth. Unlike terrestrial planting sites, roof gardens have a very precise and finite substrate depth, and it is important to know what that is in order to ensure that the root of the plant is not deeper than the substrate into which it will be planted!
- Check the size and weight. Some larger plants like trees may be specified in terms of girth and/or height, but it is always worth considering in detail how you will get the plants up onto the roof safely. The pot size will have a large bearing on the weight, and some tree root balls may add on a significant weight as well.
(Virgin Roof Gardens in Kensington)
Other issues like watering and maintenance requirements also increase in importance for larger planting schemes, and access should be considered at all stages of a roof’s development. These things may seem obvious, but if designers and installers both pay close attention to these potential problems before the plants arrive then they will enable the roof planting to run much more smoothly.