To celebrate the start of National Gardening Week, the RHS is busting the nation's biggest garden myths

“Coffee grounds deter slugs, vinegar is a good weed killer, and raised beds are best for vegetables.” These are among the myths the Royal Horticultural Society (RHS) is busting during National Gardening Week, 29 April—5 May. 

The week-long celebration with the theme ‘Knowledge is Flower’ will see RHS experts myth-bust and demystify the world of gardening and separate the facts from folk law.

To kick off the week-long exploration, Guy Barter, chief horticulturist at the RHS, unpicks some of the biggest misconceptions in the gardening world.
  1. Digging is necessary - Plants in nature don't need digging, nor do garden ones. However, digging effectively reduces weeds and occasionally relieves compact and incorporating amendments. 
  2. Deeper soil is better - Many gardeners believe the deeper the soil, the better. Around 15cm is enough, 25cm at the very most. Those planting should use sharp sand rather than costly topsoil for deep beds.
  3. Raised beds are best for growing vegetables - While raised beds can help in wet regions and clay soils, they can lead to over-draining, are expensive, and use environmentally significant resources elsewhere.
  4. Vinegar is a good weedkiller - Contrary to popular opinion, vinegar is not a good weedkiller as it won't touch grasses and only harms broad-leaved seedlings, not larger plants.
  5. Houseplants purify the air - According to our research, houseplants do not purify the air. Unlike ventilated homes with sparse plants, the original study was carried out in sealed growth chambers crammed with plants. There are plenty of other good reasons to grow houseplants, though.
  6. Coffee grounds deter slugs - The evidence for coffee grounds' ability to repel ants and slugs is poor. The same applies to myths about eggshells, grit, pumice, and many other products.
  7. Tomato leaves need to be removed - It has long been believed that bottom leaves should be removed from tomato plants. However, even lower leaves contribute to the plant until they go yellow (when they can be removed).
  8. There is no such thing as over manuring - Although many believe there is no such thing as too much manure, organic matter, or compost, this is wrong. Overmanuring leads to excess heavy metals, phosphorus, and pollution. 
  9. Tree roots go as deep as the tree is tall - Tree roots form a shallow but broad 'plate' of roots and go wide instead of deep.
  10. You need to fertilise every spring - It is believed you must add fertiliser every spring. However, most plants don't need feeding.
Throughout National Gardening Week, gardeners can join the RHS for hands-on planting with the RHS Big Seed Sow, a community-growing campaign designed to get people sowing and sharing seeds and visit one of the five RHS gardens for fantastic activities, exhibitions, and fairs to unlock horticultural secrets. Members can also take full advantage of on-site advisory teams, open at selected times across the sites and over the phone Monday through Friday for their biggest gardening questions.
To find out more about National Gardening Week, please visit


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Notes to editors

About the RHS
The Royal Horticultural Society (RHS) was founded in 1804 and is the UK’s largest gardening charity.
The RHS vision is to enrich everyone’s life through plants and make the UK a greener and more beautiful through its inspirational gardens and shows, science research and advisory, extensive library collections and far-reaching education and community programmes. With over 600,000 members, the RHS also shares its horticultural knowledge and expertise with millions of people every year through its website and publications.
In 2021, the RHS launched its Sustainability Strategy, committing to be net positive for nature and people by 2030. The supporting RHS Planet-Friendly Gardening Campaign will continue to harness the power of the UK’s 30 million gardeners to help tackle the climate and biodiversity crisis.
We are solely funded by our members, visitors and supporters.
For more information, visit
RHS Registered Charity No. 222879/SC038262

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The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.