The best lightweight compost for roof gardens

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Looking for the best lightweight compost for roof gardens? Most suitable plants? Lightest pots? Put down that heavy bag and let us help.

The best lightweight compost for roof gardens

On a hot summer’s day in the city, most people welcome the chance to chill out in the garden. If you’ve an unused roof space how about turning it into your own relaxing retreat. Or even an allotment in the sky? Plus a well-designed outdoor roof space can add 10 – 25% to your property’s value.

A rooftop garden is good news for the environment too. A cityscape’s concrete, brick and tarmac create urban hotspots, holding in heat. But a roof garden can help bounce back some of the heat in summer, and insulating what’s underneath it in the cooler months.

A major challenge of urban gardening is sourcing and storing supplies, not least when trying to find lightweight compost for roof gardens, balconies and living walls. Put down that heavy bag of compost and read on for the best nutrient-rich solution for your ‘storey’-book oasis.

A weighty matter

Before you start, you need to check that your roof is strong enough to be topped up by a garden. Structural shrubs and plants will put on weight as they gro. Heavy rain can weigh down planting. And extra friends enjoying a rooftop party will add to the load.

The Roofing Matters Group says a flat roof for a home garden needs to be able to support 45kg per 30cm x 30cm square. But do check with a structural engineer or your landlord. Better safe than sorry!

Plan twice, carry once

When starting any new gardening project, it’s always important to plan. But with rooftop gardens, it’s crucial. After all, what goes up must come down if you don’t use it!

Go old school, and sketch out your plan on paper for seating areas and planting spots. Want something more hi-tech? There are lots of free online garden planners out there.

Lighten up

To avoid any damage to your roof structure, pick a lightweight compost. Coconut coir and perlite mixes are airy, light and hold onto more air and water than peat composts. This encourages plant growth, so everyone’s a winner.

Step to it

When stairs are your only way to access your rooftop sanctuary, it makes sense to work smarter, not harder.

Traditional peat-based compost is often saturated with water, meaning a 50 litre bag of compost can weight about 10kg.

Our 75 litre Coco Coir Boost compost pack weighs just half of this: 5kg! The secret? It comes compressed, in an easy-to-handle mess-free cardboard box. When you want to use the compost, just add water, and fluff it up.

Making the right container choice

Sturdy containers don’t have to be made of stone or concrete. Consider lightweight plastic and fiberglass pots instead. To give you more of an idea, here are some average weights of 40cm high large plant pots:

  • Fibre clay pot: 10.9 kg
  • Concrete pot: 8.5 kg
  • Lightweight concrete pot: 6.5kg
  • Fibre and stone mix: 5kg
  • Plastic pot: 2.7kg

You don’t have to buy new either. Upcycle restaurant-sized oil canisters, old ceramics or even old sink. Just make sure to drill drainage holes first. If you add a waterproof lining, wooden crates and baskets can be stacked into a display.

Pro Tip: When moving plant pots around, ‘caddies’ on wheels are worth the investment to save effort and pulled muscles.

Best plants for roof top gardens

Sorted out your growing medium? Great! You can now get to planting. Some flowers plants well-suited to rooftops include:

Sunny spots: Lavender, verbena, marigolds, pansies, roses, begonias

Shaded areas: ferns, hostas, caldiums

Depending on your weight limits, dwarf trees in large pots can provide shade and protection. Lemon trees, olives and Japanese maples could work really well.

Still not sure? Try drought-tolerant plants, the kind that thrive in the Mediterranean.

Tasty treats for the table

Rooftop gardens don’t have to be just decorative. Why not use yours to grow herbs and produce? Rather than digging down, fill raised beds with our lightweight compost.

You can also grow veggies in pots, such as beetroot, tomatoes, peas and chilli peppers. Check out Growing vegetables in pots for more tips.

A hydrated heaven

Did you know trees evaporate water vapour through their leaves? A single birch tree gives off more than 300 litres of water per day.

But the higher you go, the less chance you’ll have of being underneath a tree, and the cooling shadow it casts. An elevated roof garden is also more exposed to the wind’s drying effects.

To compensate, install a water butt if you can collect rainwater from other rooftops, a drip irrigation water system, or at least a tap so you can water regularly. Luckily coconut coir compost is great at retaining water. Just don’t judge it by the top layer! Poke a finger or a pencil underneath to see if it’s damp. Don’t want your plants to dry out on a windy rooftop? Select deep, wide containers which can’t topple over.

Pro Tip: make sure your drainage is up to the job. You don’t want water puddling and causing problems after a downpour.

What’s on the menu?

Even the most low-maintenance plants need nutrition to thrive. Our Coco Coir Boost blend has in-built nutrients which will feed your plants for up to 6 months.

Rooftop inspo

Sky gardens are cherished across the world. Check out:

Namba Parks, Japan

Rockefeller Center Roof Gardens, New York as seen in films such as 2002’s Spiderman

Roots in the Sky forest, London

Tips from the ‘Green Gardeners Guild’ online advice library

Get more tips and hints on improving your green fingers by checking out our blogs:

The benefits of urban gardening

Best plants for an apartment balcony

Sustainable gardening methods for every gardener

Shout it from the rooftops

Are you proud of your high-rise horticulture? Let us know on social media! Post your pictures and tag in @cocoandcoir on Instagram. We’ll credit you for any images we use and you’ll even get £10-worth of loyalty points for any of your stories we use!