As gardeners embark on their annual spring weeding ritual, the next step of applying mulch emerges as a vital practice for cultivating healthy beds and borders. Spreading a protective layer around prized plants offers multiple benefits, from suppressing unwanted weeds and retaining essential moisture to enriching the soil with vital nutrients.
However, navigating the variety of options can be bewildering, as noted by David Stanford-Beale, PhD in entomology at MAD Company.
He said: “Nine times out of 10, a customer will choose aesthetics over almost everything. They want something that looks pretty in their garden and the same with houseplants,” he explains.
“One gardener in 10 cares about ingredients, provenance and what they actually put in their garden.”
Stanford-Beale advises consumers to examine product labels: “When you're looking for mulch at your garden center, the key is to read the bag, look for the source and, if you can, buy it locally.”
Different types of mulch are suitable for specific gardening tasks:
Compost
Whether it comes from a garden center or your own pile, compost provides crucial nutrients to hungry plants like roses and hostas while effectively suppressing weeds. Improves soil structure and moisture retention in all types of soil.
However, the RHS warns against using it near plants such as lavender or sage, which thrive in drier, nutrient-poor conditions. Gardeners should also be aware that some compost may contain weed seedlings that must be removed.
For large areas, purchasing mulch can be an expensive mulch solution, Stanford-Beale notes.
barnyard manure
This highly potent organic material excels at retaining moisture and infusing beds and borders with plenty of nutrients, making it ideal for roses, shrubs and other demanding plants. It significantly improves soil structure and is unlikely to introduce weed seedlings.
The key, according to the RHS, is to ensure the manure is completely rotted to avoid burning the plants; If it still smells bad or smokes, it requires further decomposition.
Straw
“Straw-based mulches are fine. They look and smell good, so the customer has a great reaction. They break down very quickly and release a lot of potassium into the soil,” says Stanford-Beale.
While suitable for raised beds or vegetable gardens in spring, care should be taken to avoid overwhelming young plants and new seedlings with excess potassium. “It only becomes a problem when year after year you use straw mulch and it builds up, but if gardeners are sensible about what they put in there shouldn't be a problem.”
Bark
Bark chips are a popular choice for edging as they effectively suppress weeds and conserve moisture. Stanford-Beale highlights additional ecological benefits: “If you have more moisture, you end up with less air and slightly different cycles occur in the soil, so it encourages worms and a lot of buried insects to come up through the mulch and recycle it.”
He compares its function to natural forest ecosystems, where fallen leaves act as mulch, stimulating the surrounding environment. He recommends using bark mulch around trees, ideally of the same species: oak bark for an oak tree, pine bark for a pine tree. It also highlights the importance of checking origin, discouraging treated wood and encouraging the use of products from the United Kingdom.
“People are not labeling responsibly or appropriately and this makes it difficult for customers to choose responsibly,” he warns, although he notes that some retailers are improving their labeling practices.
Non-biodegradable materials
Slate, stone chips, pebbles, tiles and even decorative glass are often used for their aesthetic appeal, while helping to retain moisture and suppress weeds.
However, Stanford-Beale cautions against its long-term implications. “That slate and glass will go on your lawn and break your lawnmower. And for the rest of the time you'll find that product in your bed.
“So if you wear something today that you like for its aesthetics, make sure you will like it in 20 years, because it will still be there.”
How deep should the mulch be?
For effective weed suppression without the need for a weed membrane, a layer of mulch should ideally be three inches deep, advises Stanford-Beale. However, he adds, “any amount helps, even if it's just a small amount to add organic matter to the soil.”
