Some half hardy annuals are tough enough to sow outside in late May and still flower prolifically from midsummer onwards. There are two key factors: choosing the right varieties and giving them the right conditions
Many of us don’t have a greenhouse and propagator in which to raise half-hardy annuals, and germinating the seeds on the windowsill often results in lank and leggy seedlings which fail to develop well. However, some are sufficiently sturdy and vigorous to sow outside in the second half of May and give a great summer display from summer into autumn. There are two main considerations: picking the right cultivars and giving them the correct conditions.
Choose varieties that germinate quickly in less than ideal temperatures, grow vigorously and flower early: so begonias, petunias and geraniums (zonal pelargoniums) can be ruled out. Look too for varieties which come in packets with plenty of seed to allow you to make allowances for some seeds not to emerge.
Cosmos (above) are among the most dependable; look for ‘Gazebo’, ‘Purity’, ‘Sensation’, ‘Sonata’ or ‘Versailles Tetra’, and even though they’re relatively tall, they grow strongly and can be spectacular in late summer. Zinnias, too, thrive when sown in May, especially the large-flowered types that are ideal for cutting; they all hate being transplanted, so the sow-where-they’ll-flower approach is ideal. Try ‘Benary’s Giant’, ‘Giant Double Mixed’ or ‘Oklahoma Mixed’.
Amongst shorter flowers I like variegated nasturtiums, ‘Alaska’ comes in both a mixture and in separate colours and looks attractive from when it has just a few marbled leaves, and French marigolds including ‘Bonanza’ (pictured left), ‘Disco’ and ‘Naughty Marietta’ all flower reliably when still small plants.
How to sow
Try to choose a sunny and sheltered place in good fertile soil that is not too heavy. Rake the surface to create a fine texture and then, following the guidance on the seed packets, draw drills in the soil with the point of a stick. Carefully soak each drill with water from the spout of a can, as this gives the seeds instant access to moisture. Sow the seeds thinly, and cover with soil.
When the seedlings have one or two true leaves, thin them by placing two fingers on the soil on either side of the ones you wish to keep to ensure they’re not disturbed then pull out the seedlings in between. Thin to half the final distance recommended on the packet, then two or three weeks later remove alternate plants.
The plants should grow strongly and flower well, and you’ll have grown an attractive range of half hardy annuals without any indoor equipment.