The Hemp Mulch Seasonal Calendar: When and How to Mulch in the UK

Spring: March to May

Spring is the most important mulching window of the year and the one most British gardeners miss. The ideal moment is when the soil has warmed above 7°C but before the main weed flush begins — typically late March to mid-April in southern England, and early to mid-April further north.

Apply hemp shiv to a depth of 5 to 7cm across all beds, keeping a 10cm gap around the base of established plants to prevent collar rot. This spring application suppresses the first wave of annual weeds before they germinate, locks in soil moisture ahead of the drier months, and creates the abrasive surface barrier that deters slugs just as they become active.

For vegetable beds, wait until after you have sown or transplanted, then mulch the pathways and the spaces between rows. Hemp is light enough that it will not compact seedling emergence the way heavier wood bark can.

Summer: June to August

If you mulched well in spring, your summer task is largely one of maintenance. Check the depth of your hemp layer in late June — it will have compressed and started to break down. Top up any areas that have thinned to below 3cm, paying particular attention to south-facing beds that receive the most direct sun and lose moisture fastest.

During heatwaves, hemp's water-retention properties are at their most valuable. The shiv acts as a thermal blanket, keeping soil temperatures significantly cooler than bare earth and preventing the surface crust that blocks water absorption. Gardeners who mulched in April typically need to water 30 to 50% less frequently during a hot July than those with bare soil.

Autumn: September to November

Autumn offers the second major mulching opportunity of the year, and it is especially important for perennial borders and fruit trees. As herbaceous plants die back in October, clear away dead foliage and apply a generous 7 to 10cm layer of hemp shiv across the entire border. This acts as insulation against the first hard frosts, protecting the crowns of marginally hardy perennials and the feeder roots of shrubs and trees.

The autumn application also sets up the soil biology for spring. As the hemp slowly breaks down over winter, it feeds the earthworm population and builds mycorrhizal networks that will power next year's plant growth.

Winter: December to February

For most gardeners, winter is not a mulching season — but it should be for specific tasks. If you have root vegetables still in the ground (parsnips, carrots, celeriac), a thick 10cm layer of hemp shiv over the bed acts as insulation, keeping the ground workable and preventing the roots from freezing solid during cold snaps.

Container plants left outside benefit from having the top of the pot covered with 3 to 4cm of hemp to protect shallow roots from frost. It is a simple step that can save tender perennials that would otherwise need to be moved under glass.