Jeff McMillan lives in Shoreditch in London, where green spaces are not in clear abundance. However, rooftop spaces are on almost every building in the area and like his, are a perfect space to grow food and use as a recreational space. He started growing his own food in 2005 and has found the experience of growing in the centre of London very rewarding. Jeff realizes that there is an increasing pressure on allotment spaces, which for him, are often in areas where he has to drive or cycle to get to. The fact that he can pop upstairs and he has his own produce flourishing is a dream for an urban dweller. It is not only great due to the edible produce but it has also created an aesthetically pleasing space to relax and eat in. Jeff signed up to Landshare in 2010 in order to encourage other urban dwellers to do the same and has found it astonishing that there is so much unused rooftop space that is perfect for growing on. "I joined Landshare because it could encourage others to do the same. And it’s a great tool for networking. I thought I might be able to learn a few tips from other urban gardeners or offer some advice of my own." Here he writes about his experience of rooftop growing.
Number one consideration: weight
Roof gardening in the city can be a fantastic way to supplement or even wholly supply yourself with edibles for many months of the year. Virtually anything that can be grown in any other garden is a possibility, though there are a few key considerations to think about before beginning. The biggest one is whether the roof in question can support the weight of having pots and plants and heavy wet soil on it in the first place. If in doubt it might be good to ask a structural engineer to have a look if you are planning anything too ambitious, and in any event it’s probably a good idea to spread the load around so that weight is not all in one place. I am lucky because my own garden is on a flat concrete roof of a former industrial building, which means that weight is not a problem.
Also, it’s a good idea to make sure anything on the roof surface is not going to cause leaks later. A soft bitumen roof for instance might not be good for angular metal box containers because they might begin to gauge into the bitumen on hot summer days. On my roof I put down paving stones that rest on spacers so that they float over the asphalt for the most part. Another consideration is whether you will get a decent amount of sun and hopefully not too much strong wind. And lastly, you will need reasonably easy access to the roof if you are going to be hauling up soil and the like, and also you will want a water supply. A roof garden will tend to dry out very easily because of its exposure to the elements and because container gardening won’t have nearly the water retention of a garden planted on good old terra firma. That being said, watering once a day is usually fine.
Grow Bags and Shallow Beds
It is amazing what can grow in a pot or in grow bags, which are basically bags of compost which you slice open down the centre in order to grow your vegetables. It is certainly easy to grow tomatoes, courgettes and some of the smaller root vegetables like radishes or baby beetroot or short varieties of carrots in a grow bag or a terracotta pot that is 10 or 12 inches deep. Potatoes are pretty easy as well in large buckets or even in bags that can be rolled up and filled with more compost as they start to grow up through the soil. But these can start to get into the heavier side of things and might be pushing it on an unsupported roof.
If you do have a really sturdy roof you can build shallow beds made of wood siding using new treated decking boards or even second-hand scaffold boards can in order to save money. Another option is large metal planters, usually made of zinc that are folded and riveted together. These can be expensive in garden centres but I found a nearby heating vent fabricator who made all mine for much cheaper. I simply made him a drawing with the dimensions I was looking for (say 50 cm high x 90 cm long and 45 cm deep) and he folded and riveted them together and drilled holes in the bottom for drainage. These cost me about £30 to £40 each but were twice that in a garden centre.
The one thing that is the most work is probably getting the soil or compost up on the roof. It is surprising how much is required, and when you start lumping it up the stairs your back may have second thoughts. This is a good reason to start small and see how much you like roof gardening before getting too ambitious. On the upside, I have found that I am very thrifty about re-using and reconditioning soil each season. I add manure bought from the local city farm (£ 2 per black rubble bag, half that if you shovel it up yourself in your own bags) and blend that in over the winter, as well as adding some of my own compost which I make from accumulated kitchen scraps and the dead green growth from the previous summer’s garden.
One of the simplest things to grow is the cut-and-come-again salad like rocket or mixed saladini. These are very easy and grow virtually most of the year and require very little soil and are therefore relatively lightweight too. A seed tray can work for this or I have used old drawers with holes drilled in the bottom which are then filled with soil to 3 or 4 inches deep and then spread with a fine dusting of seeds and a light covering of soil. These will germinate quickly and as when they get full leaves can be cut with a pair of scissors, just like giving a haircut. These usually grow back 2 or 3 times though they do get increasingly a little tougher. These beds are particularly good for growing really peppery rocket that is as much like a herb, as it is a salad.
If weight is really not an issue on your roof, it is possible to venture into even growing fruit trees like apples or particularly figs, though it can take 2 to 3 years to begin bearing fruit. Fig trees are very happy with constricted roots and so do well in large containers. (My fruit trees are grown in 75 cm cubic zinc containers.) I have two apple trees (good to have pairs for fruiting) one that ripens early, and one a later variety. This means there are ripe fruit over a number of months. These don’t yield huge quantities, but it is a special treat to enjoy the fruit of your own labour. Gravel at the bottom of the containers will be needed to improve drainage and some decent manure or other organic fertilizers should be put on in the winter. Its worth looking into pruning too, as it is important to give the trees a good shape and probably not let them get too wide-ranging as it will take up a lot of your space and can mean that the branches can snap if they get too leveraged out when the fruit becomes heavy.
Terra cotta pots: from £3 upward
Zinc containers: £30 upward
Decking wood for beds: approx £20
Soil / compost: £10 per bag
City farm manure: £2 per bag
Seed packets: £1 to £2 each
Find out More
Read our how-do guide to setting up your own rooftop garden, and find out how a branch of the supermarket chain Budgeons started growing its own stock, right on the roof.