Roof Garden

This is an excerpt from the Book called “Small family gardens”  by Caroline Tilston . Continue reading to learn more about Roof Garden, thanks to the author.

Design Brief 

  • A Garden in the  sky 
  • Two seating areas 
  • Shelter from the wind 

Features 

  • Raised beds 
  • Water feature 
  • Metal floor grille 

This roof garden had to be a garden-not a terrace, not a balcony. The designer Philip Nash’s aim to ‘create a garden that could have been on the ground, and lift it on the roof’. 

Having said that, it’s not just a back garden on high, there is plenty in the garden that cleverly takes into account the problems of roof gardens and at the same time makes the most of the views. 

Tips for Roof Gardens  

I’m sure there are worse places to create garden, but a roof has to be up there on the list. Drying winds, lack of shade, weight restrictions and no soil-it’s a wonder anyone tries at all. But since the hanging gardens of  Babylon, roof gardens have proved that they can be magical spaces. Although the design possibilities are limitless, there are some basic aspects to consider: 

1 Regulations may have an impact on what you want to do. Building regulations stipulate the type of barrier around the garden and also what you can have on the floor. It’s worth checking to see if you need planning permission as well.  

2  If you have  a roof that might be turned into a garden, the first thing to do is get in an architect or structural engineer to talk about weight and whether your roof can stand having plants, soil, floor material and people on it.

3 Apart from weight restrictions, another problem is the potential for strong winds.  Any trellis will have to be attached well and plants anchored in. And to make the area more useable, it’s worth finding out where the prevailing wind comes from and forming a suitable screen. 

4 Whether you want a lush or minimalist garden, if you have plants you will have to use containers of some sort. To create atmosphere with dense planting raised beds will probably work best, but they are heavier and more expensive. Smaller containers and pots are easier to put in, but dry out more quickly and can get blown over.

Tips for Roof Gardens
Tips for Roof Gardens

5 Whatever type of container you have the plants will need a lot of water.  Containers, because of their limited soil, will hold less water than the ground. Add to this the drying effects of the wind and an irrigation system begins to look like a worthwhile labour saver. Whether you water by hand or automatically, make sure excess water can drain away and safely off the roof. 

6 As in this garden, it’s good idea to save on weight by using polystyrene or perlite instead of soil at the bottom of the containers. A peat substitute is lighter than ordinary loam-based compost. 

7 If you’re using raised beds, make sure the roots of the plants are contained well within the beds. If you have smaller containers, check occasionally to make sure the roots haven’t worked their way out and into the roof. 

8 Both the user and the environment can gain enormous benefits from roof gardens. They create green spaces in urban environments, help to remove carbon dioxide, insulate the building below, and can be enormous fun. 

Screening 

Plants are great at providing a barrier between you and the world. A single plant will do – plant a few in a row and you have a hedge. 

What hedge? 

One of the first things to decide when planting hedge is whether you want an evergreen hedge or a deciduous one, and do you want a screen all year round or something that changes with the seasons and may not be much of a screen at all in the winter? 

Then you might want do decide whether you want something formal, with sleek straight lines that you can cut to precise  shapes; or something informal, a little fuzzy but interesting. The main deciding factor for this is the way the plant grows. Plants with very tight growth and small leaves are the best for creating those razor-sharp lines. Plants that flop and have quite lax growth are never going to be cajoled into geometry. 

Hedges 

Deciduous 

Deciduous informal  

Hawthorn 

  • Great for wildlife 
  • Blossom and berries to give a change through the year 
  • Has thorns so good for deterring burglars  
  • Quite slow growing 
  • Plant at 30 centimetres apart  
  • Also try roses;  the sweet briar rose makes a lovely hedge with pink flowers in summer and lovely red hips in autumn 

Deciduous formal 

Beech or copper beech 

  • Lovely autumn colour 
  • Dead leaves are held over winter so there is some protection 
  • Need to cut off a third of the plant when it first goes in the ground to get the best growth  
  • Plan 45 centimetres apart  
  • Also try purple hazel 

Evergreen 

Evergreen Informal 

Holly  

  • Comes in many different types with different-coloured leaves and berries 
  • Prickly so good for deterring burglars  
  • Berries are good for wildlife  
  • Quite slow growing 
  • Plant at 45 centimetres apart  
  • Also try cherry laurel, with its large, glossy green leaves 

Evergreen formal 

There are lots of plants to make a formal evergreen hedge. This is the main type of hedging that people want, basically a green wall. 

Yew 

The queen of hedges, this can be cut to within an inch of its life. It can be shaped into lines so sharp you can cut yourself and once it starts growing nothing is going to get through its dense growth. It’s also a good low-maintenance plant: if you cut it after the middle of August it only needs one cut a year. Compare this to privet, which can need trimming two or three times.

Green Roofs
Green Roofs
Hedges
Hedges

Box  

Another great evergreen with tight growth and smell leaves. The only trouble with box is that, if you want a decent – sized hedge, you need to plant if when you’re about 15to enjoy in your old age. (I’m exaggerating, but it will be about 10 years before it gets to 6 feet).  you can buy big plants but, because it’s box is so slow growing, these are really expensive: you’re paying for a nursery to have locked after and housed the plants for a decade. Nevertheless, box is great for low hedges. 

Privet 

Privet is a good evergreen plant, but it’s kind of boring. And why, if you could plant, but it’s kind of boring. And why, if you could plant dramatic, dark green yew, would you want to put in so-so green privet? It also takes more looking after and needs to be cut at least twice a year. 

How to plant a hedge  

Usually with hedges you buy them bare root – quite literally they are dug out of the ground in the nursery, the soil is shakes off and they are sold to you. Bare root plants are only available in winter when the leaves are off deciduous plants (like beech and hornbeam). The deciduous plants are line with the disruption at that time of year, and even evergreens can tolerate being handled this way in the winter, but treat them gently, and keep the roots covered and most even if they’re not in the ground. 

You can buy your plants in containers, but they will be more expensive, and when you’re doing a hedge and might need 50 or so plants the extra cost of each individual plant can mount up. However, in a container the plants are available and can be planted all year round (as long as the ground not frozen or the weather’s so hot they will be too stressed and thirsty). 

1 Dig a trench large enough to take the roots with ease. Use string and a tape measure to get a straight line. 

2 Work up the soil in the bottom to help the roots get a foothold. 

3 Put the plants in and cover round the roots with soil. Make sure the plant is planted at the same depth as it has been in the field – you will see the colour change on the stem. Really firm the plants in so there aren’t any big air pockets. Use a measure to make sure the plants are an equal distance apart. 

4 With deciduous plants (such as beech) cut off a third of the top growt6h just after you’ve planted them. This will encourage them to bush out. 

What is a green roof? 

If there are plants on the roof, it’s a green roof. The plants could be sedums or even moss, and they can be planted in a way that couldn’t by any means count as a garden, with no real access for people. At the other end of the scale there are full-blown gardens on high with trees, shrubs, seats, the works. 

There’s a little bit of jargon that the people who do green roofs use: 

Intensive systems are garde3ns on roofs. They might have trees and seating areas ground level.  
With all these plants and access they need a depth of soil or some growing medium and enough strength to be safe for people to use. 

Extensive systems are low maintenance, with a self – sustaining plant community’. You have these for the way the roof looks, for the sake of the building and for the environment, rather than for use as a garden. 

What’s so good about a green roof? 

  • Insulation – it helps with the heat insulation of the building. 
  • Sound reduction – it protects the building from noise.  
  • Protection – it shields the roof surface from ultraviolet rays. 
  • Decreases flood risk by soaking up rainwater. 
  • The water instead travels through the plants and is released back into the air and acts as a natural coolant.  
  • Improves the air quality by soaking up carbon dioxide, releasing oxygen and water vapour, and absorbing organic volatiles. 
  • Provides a habitat for birds and insects. 

Questions about Green Roofs 

Karen Tarr from Blackdown Horticultural Consultants Limited, specialists in green roofs, answers some question about green roofs. 

  1. Don’t they let water into the building? 

          No, quite the opposite in fact. A correctly installed green roof system will prolong the life of the waterproofing by protecting it from ultraviolet rays and the elements. It is important that the waterproofing is thoroughly checked and renewed if necessary prior to installing the green roof. 

  2. Isn’t the whole thing really heavy with soil and water? 

          We don’t use soil; we use special lightweight growing mediums that retain just enough water for the plants. Plants like sedums require only shallow growing medium for their roots, which helps to keep the weight down too. The deeper the growing medium needed (for shrubs and even trees), the more the whole planting will weigh. 

  3. Isn’t it difficult to install and look after? 

          Provided it’s the green roof has been well planned it should be quite straightforward to out in and the extensive systems are specially designed to be low maintenance. Like any new planting it needs watching for weeds in its first year, but after that it’s generally a once a year job. 

  4. What happens after five or ten years? 

          If correctly designed and with minimal maintenance, the green roof should last for many years and prolong the life of the roof’s waterproofing considerably. 

  5. Why do you use sedums? 

          They are particularly suited to the tough conditions on the roof: they are evergreen. Self – generating and drought resistant. A slight increase in the depth of the substrate will support other plants like certain types of primulas, iris, Dianthus and Potentillas. With a further increase in the depth of the substrate, more upright species such as grasses and wildflowers can be used. 

  6. If you’re got a sloping roof, can you still have a green roof? 

          You actually need a bit of a slope to allow water to run off (between two and eight degrees is ideal) and we have developed successful methods of preventing slippage in steeper roofs, although these can be more expensive to install. 

Roof Garden
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