No longer are gardens simply limited to the ground, whether you have little space or just want to maximise planting potential, green roofs are the latest craze in the gardening world.
Beautifying your green roof is going to take a little more prep than your standard patch of garden, however with the right products you can get your plants reaching for the sky in no time and if you put in the work now, then maintenance going forward should be minimal.
First things first, can the structure hold the amount of weight you are planning to have it support? A simple green roof usually weighs between 60-150kg per metre squared. However if you have more complex plans then it may be worth consulting a professional before you go any further. Also it is important to remember, you will need to take into account the full weight of the roof when saturated, not just the dry weight.
A green roof consists of several layers: Firstly a waterproof and root proof membrane lines the roof and prevents the plant life damaging the structure of the building. Secondly, a drainage board can help to channel rain off the roof and minimises saturation.
Then comes the substrate, a depth of 70-200mm is ideal. It is best to use a lightweight, low nutrient substrate as general garden soils have a high organic content that will be extremely heavy when wet. Our Earth Cycle range of Green Roof Substrates are created from BS 3882 Topsoil and our PAS100 compost, combined with Shire Ultralite that is made entirely from secondary sources, such as crushed aircrete, brick fines and expanded clay. These products are designed to make the substrate growing media lightweight and are perfect for this type of project.
Finally, it is time for planting! Planting can be done in two ways, either by using pre vegetated blankets or by seeding. Wildflowers are an excellent choice if you are keen to make the roof a floral feature, as they do not require much nutrition and are fairly tolerant of harsh conditions. Cows slip, rockrose, harebell, hawkweeds and thyme are all good choices. It is always best to choose a variety of plants for your roof as the success of a self-contained plant community is increased when mixed species are used.
The maintenance of a green roof is usually fairly minimal dependant on how lavish your chosen plant life. However, a few checks should be made once or twice a year to ensure your green roof flourishes for years to come. During the first year make sure you water your roof in dry seasons to help the plants gain good coverage. After that you should only need to water in extreme droughts of 6 weeks or more. Apart from this it is important to ensure your draining outlets remain clear from debris, and any bare areas that appear are patched up with seeds.