Gardening expert explains the key thing to check when buying mulch for spring, with advice on choosing between compost, bark, manure and other options
Mulching around a tree with bark chippings(Image: Alamy/PA)
Once you’ve tackled your spring weeding duties, mulching is typically the next job on the list – spreading a protective layer around your cherished plants in beds and borders, whether to keep weeds down, lock in moisture or enrich your soil. But which type of mulch works best for different tasks?
Many gardeners struggle when selecting appropriate mulches, according to David Stanford-Beale, doctor of entomology at MAD (Make A Difference) Company, which develops and sells organic, sustainable and peat-free growing media products.
“Nine times out of 10, a customer is going to choose aesthetics over nearly everything. You want something that just looks nice in your garden and the same with houseplants. The one gardener out of 10 cares about the ingredients, the provenance and what they are actually putting in their garden,” he says. “When you’re looking for a mulch at your garden centre, the key is read the bag, look for an origin and, if you can, buy local.”
Different varieties of mulch are designed for specific purposes.
Compost
Whether you’ve made it yourself or picked it up from a shop, compost delivers essential nutrients to demanding plants like roses and hostas, while simultaneously keeping weeds under control. Apply it to all soil types to help preserve moisture levels and enhance soil structure, though the RHS cautions against using it around plants such as lavender or salvias, which thrive in drier, less nutrient-rich conditions.
A spade full of compost(Image: Alamy/PA)
Additionally, bear in mind that certain composts might harbour weed seedlings, requiring you to remove them as they emerge. That said, if you’re covering substantial ground and aren’t producing your own compost, purchasing bagged varieties for mulching purposes can prove remarkably costly, Stanford-Beale warns.
Farmyard manure
This exceptionally nutrient-dense material excels at retaining moisture whilst delivering abundant nourishment to soil in beds and borders, making it ideal for roses, shrubs and other demanding plants. It enriches and enhances soil composition, and you’re unlikely to encounter weed seedlings within it.
The crucial consideration is ensuring the manure has properly decomposed, otherwise it risks scorching your plants, the RHS cautions. If it’s giving off odours or producing steam, you’ll probably want to let it mature further.
Spreading farmyard manure over a garden bed(Image: Alamy/PA)
Straw
“Straw-based mulches are OK. They look and smell nice, so the customer has a great reaction. They break down really quickly and release loads of potassium in the soil,” says Stanford-Beale.
“It’s fine to use a straw mulch on a raised bed or allotment in spring, but you need to make sure that younger plants, brand new seedlings, don’t get too much potassium all at once. It only becomes an issue when you go year after year after year with straw mulch and it will build up, but if gardeners are sensible about what they are putting in, there shouldn’t be any problems.”
Bark
Numerous gardeners opt for bark chipping mulch throughout their borders to suppress weeds and preserve moisture, and it offers additional advantages too, Stanford-Beale notes. “If you have more moisture you end up with less air and get slightly different cycles going on in your soil, so it encourages worms and lots of burying insects to come up through that mulch and recycle it around. It’s like what happens in the forest and in nature, the leaves will come down, act as a big mulch and stimulate the ecosystem around it to pull that nutrition down.”
It’s important to get the right type of mulch(Image: Alamy/PA)
He suggests applying bark mulch around tree bases – though it’s best to match the bark type to your tree species.
“If you have an oak tree, try to use oak bark. If you have a pine tree, use pine bark. But be careful where you are sourcing it from.”
Check the packaging to confirm the bark originates from the UK and steer clear of mulches containing treated timber, he advises, though this isn’t always straightforward to determine.
He warned: “People are not labelling responsibly or properly and it’s making it difficult for customers to choose responsibly, but places like Crocus and Blue Diamond Garden Centres are starting to do that, where they make sure that their suppliers label what the product is and what it’s made of.”
Dr David Stanford-Beale(Image: Hannah Stephenson/PA)
Non-biodegradable options
Slate, stone chippings, pebbles and shingle are frequently deployed as mulch to improve border aesthetics, and they’ll help retain moisture and keep weeds down, as will ornamental glass in containers, but Stanford-Beale highlights the potential drawbacks they present. “That slate and glass will go on to your grass and break your lawnmower. And for the rest of time you’re going to be finding that product in your bed. So if you use something today which you like because of aesthetics, make sure you’ll like it in 20 years, because it’s still going to be there.”
What depth should your mulch be?
“If you really want to suppress weeds and don’t want to use a weed membrane, your mulch needs to be three inches deep,” he suggests. “But any amount helps, even if it’s just a scattering to add organic matter to your soil.”
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