Guide To Mulching

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What is mulching?

Mulching is the practice of spreading a covering of some description over an area of ground to retain moisture in summer, to protect the roots of plants in the winter and to inhibit weed growth all year round.

Benefits of mulching

  • Helps soil to retain moisture and prevents excessive evaporation during the summer, warm weather or dry spells
  • Provides soil nutrients
  • Reduces the amount of time spent on background tasks such as weeding and watering
  • Protects plant/crop roots from extreme temperatures
  • Soil erosion during the winter or in heavy rain can be less
  • Restricts weed growth by preventing light from reaching the soil, and triggering growing messages
  • Improves soil texture by gradually breaking down
  • Makes it difficult for some pests to thrive whilst attracting insect predators
  • Helps to prevent edible crops resting on the soil by supporting them to prevent rotting, e.g. strawberries
  • Gives the garden a neat and tidy appearance

Types of mulch

Biodegradable mulches

These mulches break down gradually over time to enrich the soil by releasing nutrients and helping to improve its structure. They also improve conditions for earthworms who will, in turn, improve the soil structure and encourage plant growth. All these improvements will attract insect predators such as spiders and beetles, and they’ll help to keep some insect pests under control. The layers of biodegradable mulches will need to be replaced once the material has rotted, and should probably be topped up about once or twice a month.

The best biodegradable mulches are:

  • Leaf mould (well-rotted leaves which won’t add nutrients, but are very good for soil structure and weed suppression)
  • Garden compost
  • Grass cuttings (in thin layers to avoid it rotting down to a smelly mess) – not suitable if treated with weed killer
  • Well-rotted manure
  • Straw (can be laid in deeper layers as it will settle) – ideal for strawberries, courgettes and other crops that need to be kept off the soil surface
  • Wood chippings or processed conifer bark such as landscape bark or Westland Decorative Mini Bark (£7.99 2 for £14)
  • Westland Gro-Sure Smart Ground Cover (£11.99)

Non-biodegradable mulches

These mulches will not boost the structure or content of the soil, but will suppress weeds, restrict evaporation and can add a finishing touch to borders or beds. Permeable sheet mulches are also available, although they will need to be covered by other materials to make the area less stark. These all exclude the light that weeds need to grow, but still allow rain to reach the roots of your plants.

The best non-biodegradable mulches are:

  • decorative aggregates such as slate, shingle, pebbles, stone chippings or gravel
  • sea glass, sea shells or small grade aggregates can be used on smaller scale projects such as pots or wall baskets
  • landscape fabric/weed control fabric (can be covered with aggregates once laid)
  • Thick brown cardboard sheets or multiple layers of newspaper can also be used on bare soil areas (overlap the sheets by 30cm and weigh them all down with rocks or bricks). They will not offer nutrients, but they will degrade and will suppress weeds.

When and how to apply mulches

Mulches are best applied from mid to late spring and in the autumn, when the soil is warm and moist. Avoid putting mulches down in cool, damp periods as this may encourage slugs.

  • Mulches can be used on bare soil and on the top of containers
  • Lay over moist soil after completely clearing the area of weeds
  • Biodegradable mulches need to be laid to a depth of about 7.5cm (3”) and topped up periodically as they rot down
  • Individual trees and specimen shrubs should be mulched to the radius of the canopy
  • Avoid piling mulches around woody stems as it could make them vulnerable to disease
  • Be careful not to smother low-growing plants
  • Remember to water more thoroughly once the mulch has been laid so that the water will reach the plant roots

If planting through mulch sheets, cut a slit in the sheet and plant as usual through the slit, laying the fabric flat again around the new addition.
When planting through an organic mulch, clear the area of mulch, dig the hole and put the plant in as usual. Water the plant in and then push the mulch back in place, being careful not to overwhelm the plant.