Q I've found some spring-flowering bulbs that I forgot about. Is it still worth planting them?

A  Which? Gardening magazine looked at the effect of planting six different types of popular spring bulbs at different times, from mid-September to early January to find out.

Caption: Will you get flowers if you plant bulbs late?

Q How late can I plant daffodils?

A The best results for early flowering Narcissus ‘Tête-à-tête’ came from planting in early October, producing plants that spent four weeks in full flower in March. But we still got good results with bulbs planted as late as December, although the time spent in full flower was halved. Those planted in January were shorter, later and spent two weeks less in flower.
There was even less difference with later-flowering Narcissus ‘Passionale’ – they all flowered well and for a similar length of time in mid-April.
WHICH? GARDENING MAGAZINE VERDICT Early autumn is best, but even December plantings can give a decent result.

Caption: Narcissus 'Cedric Morris'

Q How late can I plant tulips?

A Traditional advice is to plant tulips later than other bulbs, in mid-to-late autumn, to reduce the risk of tulip fire. Late-October and November plantings gave us the best combination of emergence, flowering duration and good-quality flowers. We suffered losses of up to 25% with tulips planted in September and early October. The bulbs lasted well, remaining firm and unsprouted. But early ‘Red Riding Hood’ tulips planted in December and January emerged later, were shorter and spent less time at full flower. May-flowering ‘Queen of Night’ was least affected by delayed planting, although they flowered for less time.
WHICH? GARDENING MAGAZINE VERDICT Late October and November is best, but you can delay planting late-flowering varieties.

Caption: Tulipa 'Queen of Sheba'

Q How late can I plant Crocus tommasinianus?

A There was little difference between crocuses planted in September and early October. Nearly all the bulbs came up, and the overall flowering period extended over 63 days, with most corms spending a month in full flower from mid-February. Later-planted bulbs started flowering later, peaking in late February to early March, and spent just a fortnight in full flower. Although the
crocus corms remained firm until January, they started to sprout from early October. Only 60% of the crocus planted in January survived and they produced less spectacular-looking flowers, too.
WHICH? GARDENING MAGAZINE VERDICT Plant in September or early October for a long-lasting and early display.

Q How late can I plant grape hyacinths?

A  Muscari bulbs planted in September and early October had leaves all through the winter and produced the best display of flowers, lasting for five weeks at full flower, towards the back end of March. The bulbs developed some roots and shoots if they were kept for longer, but later-planted bulbs survived just as well as the early-planted ones. They developed to about the same height and flowered nearly as well as earlier ones, putting on a great display that lasted for four weeks until the start of April.
WHICH? GARDENING MAGAZINE VERDICT Plant whenever you like as it makes little difference to the flowering time or flower quality.

Caption: Grape hyacinths (muscari)

Q How late can I plant Allium 'Purple Sensation'?

A Alliums planted in September emerged in March to give us the longest total flowering period of five weeks, and spent two weeks in full flower in May. Bulbs planted later than that were in flower for a week less, but the displays were still good and the flowering period was only delayed by a week or two. The bulbs developed some signs of mould in October and had formed small shoots by January. However, emergence was good and later planting didn’t seem to affect the quality of the flowers.
WHICH? GARDENING MAGAZINE VERDICT September is best, but alliums still flower well from later plantings.

Caption: Allium 'Purple Sensation'

Q How late can I plant Iris reticulata?

A All of the irises we planted were in full flower for two weeks, but those planted in September and early October gave us the longest overall flowering periods of eight and seven weeks, and the best quality flowers, too. Bulbs stayed firm but began sprouting in November, which made them a bit harder to plant by January. Fewer bulbs emerged from November plantings onwards and they flowered later. Irises planted in December and January were up to 25% shorter than earlier plantings, and the flower spikes didn’t come up straight – instead they bent over.
WHICH? GARDENING MAGAZINE VERDICT Plant in September or early October for good displays of early colour.

Caption: Iris reticulata 'Rhapsody'