Action plan: Nigel Colborn's essential jobs for your garden this week 

Action plan: Nigel Colborn’s essential jobs for your garden this week

  • Tender plants are no longer safe from frost outside in any part of the UK 
  • Nigel Colborn says those grown as annuals can be composted or discarded 
  • Gardening expert recommends preparing for low night temperatures now 
  • TAKE TENDER CUTTINGS 

    Tender plants are no longer safe from frost outside in any part of the UK. Those grown as annuals, such as tagetes and petunias can be composted or discarded.

    If you want to use pelargoniums, fuchsias and heliotropes again next year there are two options. The first is to pot up mature plants, trim away excess growth and bring them into a greenhouse or conservatory. They could be feature plants next year.

    The second is to root cuttings now for planting out next May. All but begonias are easily raised from small cuttings. Gather those as soon as you can, taking only the young shoots, preferably with no flowers.

    Gardening expert Nigel Colborn says tender plants are no longer safe from frost outside in any part of the UK

    Gardening expert Nigel Colborn says tender plants are no longer safe from frost outside in any part of the UK

    When you have seed trays or pots handy, fill them with fast-draining potting compost. You can improve drainage further by adding extra coarse horticultural sand.

    Remove any unopened flower buds from your cuttings and make a clean cut, preferably across a joint where the lowest leaf was attached. Insert each cutting into the compost. Water thoroughly.

    Cuttings will root rapidly if the pots are placed in a heated propagator. You can buy one for as little as £13, but there are large and better models under £40. The compost will be kept at about 20c ideal for fast rooting.

    FROST ALERT 

    A freeze is unlikely before December, but it’s good to prepare for low night temperatures. Unheated greenhouses are safe but not frost-free. Check that doors and vents are close-fitting. Have horticultural fleece handy to place over vulnerable plants at night. It will keep them 1c to 2c warmer than if left unprotected. Spread mulch around other plants to safeguard roots.

    DIG UP YOUR DAHLIAS 

    Dahlias can be lifted now, or after the autumn’s first frost. You can cut away all top-growth, leaving short stumps. The tubers can be stored dry.

    However, they will also keep well if planted in large pots somewhere that is frost-free.

    Dahlias left in the ground will need extra protection. Surround them with thick mulch such as potting medium, home-made compost or leaf-mould as a frost buffer.

    READER’S QUESTION 

    Several of my colchicums have a few flowers left. Some of the clumps are congested. Can I dig those up and split them? If so, when is the best time?

    Dorothy James, via email. 

    You can divide them, but now is not a good time. Colchicums are not fully dormant until their spring top-growth withers. They’ll be dormant from then until late August. It’s best to dig up the plants when old top-growth is still visible. Tease the clusters apart then plant bulbs about 10cm (4in) deep.

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