Containers, compost, and keeping them fed

Most cut flowers resent sitting in wet compost. Use a loam-based mix like John Innes No. 2 or No. 3 for perennials, or a 50/50 blend of multipurpose and grit for annuals. Add a tablespoon of slow-release fertiliser (blood, fish and bone, or a balanced Osmocote) per 10-litre pot at planting time. Ensure drainage holes are clear — raise pots on feet in winter to prevent waterlogging.

Size matters. A single sweet pea climber wants at least a 25cm pot and ideally a 30cm one; three cosmos plants share a 35cm container comfortably. Window boxes need to be at least 20cm deep for anything beyond salad leaves. Grow bags are brilliant for annuals — cut three large drainage slits in the base, fold the sides down to 15cm, and sow direct. A single bag will take eighteen nigella or twelve cornflowers. Feed weekly once flowering begins: liquid tomato food at half strength is perfect for most annuals (dilute 15ml per 5 litres). Over-feeding produces soft growth and floppy stems.

Water is the variable you control. Most cut-flower annuals want consistent moisture during growth but dislike soggy roots. Water deeply twice a week rather than a daily sprinkle. In high summer, pots on sun-baked balconies may need daily watering — check by lifting the pot; if it feels light, water until it runs from the base. Mulch with a 2cm layer of fine bark or spent compost to reduce evaporation. Do not use moisture-retaining crystals — they encourage root diseases and weak stems.