What Makes a Good Green Roof Fertiliser?
Green roof fertilisers, like most garden fertilisers, contain the three primary plant nutrients:
- Nitrogen (N): Used by plants for healthy leaf growth and green colour
- Phosphorus (P): Used in the formation of new roots
- Potassium (K): Helps plants build strong stems and promote fast growth.
Alongside an assortment of minor nutrients that vary depending on the type of fertiliser you choose.
But whatever you do, don’t use regulation strength plant or vegetable fertiliser for green roofs.
What Should I Feed Sedum Plants and Green Roofs?
Because green roof plants – typically sedums and succulents – don’t need nutrient rich soil, or fertiliser, to survive and thrive. In fact, nutrient dense substrates and fertilisers are the antithesis of what your green roof needs. The best substrates are low nutrient and porous.
Extensive and semi-intensive green roofs are typically made up of sedums and wildflowers – plants that are low weight, low maintenance and pretty hardy.
If you provide your green roof with too much nitrogen and potassium, the plants will grow too high, too quickly. This damages your roof’s insulation properties, stability and puts the plants at greater risk from the elements.
So you need a low-nutrient, N-P-K balanced fertiliser, with roughly equal parts nitrogen and potassium and around half as much phosphorus. So. Don’t go rogue and think you need a strong fertiliser to blast roof growth. That’s stupid. And we’re not stupid. We’re lazy gardeners. Not stupid ones.
Best 6 Sedum Fertilisers
Natural Fertiliser for Organic Growers
- 15.99
- 2 litres
- 4.7 from 44 reviews
- 100 litres of water once mixed
- A low carbon alternative
Natural Grower’s Organic Fertiliser is a natural fertiliser for organic growers. The lack of chemicals is perfect for sustainable green roof growth as there’s no chance of burning the plants or the roots themselves and causing lasting damage.
And given the almost ideal NPK ratio – 3.6 – 1.5 – 3.7 promotes sustainable growth and mitigates any chance of over-feeding. As long as you use it sparingly, which we hope by now is obvious.
And as it’s made from the by-product of maize, it’s a largely sustainable, plant-based liquid fertiliser. The only concern we have is the fact it needs mixing with water – so careful of drainage, roof weight and runoff.
Biotope Aquatics Organic Succulent Fertiliser
- 9.99
- 150ml
- 4 from 13 reviews
- Spray application ideal for long-lasting green roof fertilisation
Biotope Aquatics Ltd Organic Air Plant Fertiliser – quite the mouthful – is the only spray applicator on the list. And if you’re looking for an easy, organic fertiliser that won’t overdo the nutrients, this is a great option.
Perfect for smaller roofs – shed or otherwise – and one of our favourite succulent and sedum fertilisers.
Garten Gluck Succulent Plant Feed
- 10.99
- 250ml
- 4.3 from 82 reviews
- Enough for multiple seasons of feed for extensive green roofs
Garten Gluck’s Succulent Plant Feed is ideally suited for the average at home extensive green roof.
The pipette application system means you will never overdo the feed and can apply it to individual plants. Which can be a real roof-saver when trying to prevent over-feeding.
Whilst it is organic and chemical-free – ideal for biodiversity – some ingredients are toxic to cats, so take care when applying.
Turf Online Sedum Fertiliser
- 23.95
- 2kg
- 4.6 from 14 reviews
- 65m² coverage - although the deeper your soil is, the less the coverage will be
Turf Online’s Sedum Fertiliser has been perfected for sedum roofs. It’s slow-release, organic formula is designed to create stable, rich looking flowers that don’t grow leggy or burn root systems or the plant itself.
The best part – it should brighten up your roof within a couple of days. So if you’ve recently built a green roof and the winter wet has stripped it back to a slurry
Hexafrass Natural Organic Fertiliser
- 11.56
- 12kg
- 4.6 from 27 reviews
- 150m² + coverage
Hexafrass is a slow release fertiliser that boasts a high organic matter content & bioavailable nitrogen (fortunately not too much).
It’s 3-1-1 NPK ratio is a little light on the potassium, but low enough overall that plant growth will be steady and sustainable. Plus this certified organic fertiliser’s (produced by Black Soldier Fly larvae) lack of chemicals make it perfect for fostering a wildlife-friendly habitat and increasing biodiversity.
It’s also completely free from potentially damaging manmade chemicals and doesn’t require water solubility – it is dried, milled & ready to use! So no damage of excess water retention, runoff or roof weight.
Miracle-Gro Growmore Granules
- 6.56
- 3.5kg
- 4.6 from 205 reviews
- 150m² +
Miracle-Gro’s growmore granules is a low-medium nutrient, well balanced soil that’s an ideal top dressing to add to your green roof for a few reasons:
- Balanced 7 – 7 – 7 NPK ratio (a little heavy on the phosphorus but that’s ok)
- Lightweight and easily spreadable (no water solubility required)
- Promotes strong root growth, so it should increase stability without the plants getting too leggy
This classic, all-purpose fertiliser works a treat on typical DIY green roofs, just use sparingly to begin with as it isn’t chemical-free.
Westland Cacti & Succulent Plant Feed Concentrate
- 3.99
- 200ml (5ml per litre)
- 4.6 from 2,000+ reviews
- 40 litres of water once mixed
Westland’s low nutrient, concentrated formula has been developed with low nutrient plants in mind. Sedums and cacti are famed for their ability to store water and nutrients in their leaves, so overfeeding them would put them more at risk of disease and elemental damage.
The downside to this formula is that it’s designed for potted plants and houseplants. So whilst it’s easy-measure applicator is great for a litre of water, it’s not designed for larger scale applications.
AND – be careful of over-watering your roof. The extra weight and pressure this puts on your drainage system and waterproof cover means this is only suitable for smaller roofs with a solid drainage system.
Best Green Roof Fertiliser Spreaders
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Greenkey Deluxe Seed and Fertiliser Spreader
Greenkey’s Deluxe Fertiliser Spreader has a 3 litre capacity, is lightweight (so perfect for extensive green roof spreading) and will make fertilising even larger garage or shed roofs a dream. Perfect for lazy gardeners such as ourselves.
It’s also a steal at £17.99!
Evergreen Whizz Year-Round Spreader
If you want to be a little fancier – and you love tech products as much as I do – then you should invest in a battery-powered spreader.
Evergreen’s Whizz Year-Round Spreader is great value at £26.30 (batteries included), has 23 different speed and spreading settings that make fertilising semi-intensive, or even intensive roofs 100 times better.
It becomes fun. Imagine that. Fun-fertilisation.
Green Roof Fertiliser FAQs
Firstly the fertiliser should be as natural as possible because we (generally) want to encourage wildlife habitation and biodiversity.
Then the fertiliser cannot be too nutrient rich. It must encourage slow, sustainable growth so plants don’t get too leggy. Typically an NPK blend of somewhere around 8 – 4 – 8 is perfect.
If you have a green roof then you need to help ensure that it is able to grow and stay strong throughout the year. Whilst they don’t require much maintenance, living roofs usually need some fertiliser to remain healthy all year round.
Most living roofs are sedum dominant. And sedums are succulents, meaning they store water and nutrients in their fat leaves. This enables them to survive the tough conditions and that they can endure the soil of arid climates that is typically poor in plant nutrients. As a result, they don’t need much maintenance or fertiliser to thrive.
A handful of all-purpose granular fertiliser sprinkled on the soil each spring is generally perfect for sedums. If a sedum is growing in relatively nutrient rich soil then we recommend leaving it until the plants start to look weathered before fertilising. It’s like adding salt. Once you’ve done it you can’t take it away.
Dry granular fertilisers must be watered into the soil. And be careful when using water soluble fertilisers because you definitely don’t want to overwater your roof.
A lot, but here are the core points of consideration:
- How much weight can your roof support?
- What are the weather conditions like where you live? Will adding additional water present a problem?
- Structural solidity
- Foot traffic – is the roof in use by people?
- Drainage and runoff capabilities
- Biodiversity – will using chemical formulae harm the environment?
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