Greenhouse calendar - March
March is the first month of spring, bringing with it the prospect of warmer weather as days lengthen and sunshine levels increase, but the transition from winter to spring isn’t always smooth and frost and snow are still likely. Make the most of any good weather to finish off any maintenance jobs before plants start back into growth.
In the garden:
- Cover the ground with black plastic to warm up the soil in beds where you plan to sow seeds.
- Remove weeds as they start to appear.
- Finish cutting back ornamental grasses and herbaceous perennials at the start of the month, but leave borderline hardy perennials such as penstemons and pennisetums until April or early May to protect new growth from late frosts.
- Refresh container plants by scraping away the top 5cm of compost and replacing this with a fresh layer. Acid-loving plants will need ericaceous compost and for shrubs use a John Innes No 3 compost, as it releases nutrients over a longer period.
- Divide perennials such as hardy geraniums, astrantia, hostas, nepeta and heleniums every 2–3 years to reinvigorate the plants.
- Divide snowdrops after they finish flowering.
- Cut the lawn – choose a dry day and use the mower on its highest setting.
- Remove the old flower heads on hydrangeas.
- Feed strawberry plants with seaweed meal.
- Start to water and feed houseplants, and repot those that have become pot bound.
- Pot up dahlia tubers into large pots filled with multipurpose compost towards the end of the month. Keep them somewhere frost-free until they can be hardened off in May.
In the greenhouse:
- Sow hardy plants this month: peas, salad leaves, rocket, radish, beetroot, and flowers such as scabious, sweet William, calendula and cornflowers.