I'm assuming that if someone asked Kathleen Sayce about this, they
live near her, on the Pacific Northwest coast. Many of the plants
people have recommended, although thought to be "hardy in Zone 8" ,
would not survive winters there, especially in a planter above
ground. The USDA zone ratings simply don't work west of the Rocky Mountains.
Some bulbs that I have in summer-irrigated areas include hybrid
daffodils, Fritillaria meleagris, Eucomis species and hybrids,
Ipheion (already mentioned), Galanthus, Corydalis solida selections
('Beth Evans' is widely available in garden centers now), Cyclamen
hederifolium (will grow anywhere in this region), Erythronium
revolutum, many Muscari, Tulipa sylvestris, Crocus vernus forms, and
many Arum species. The Eucomis can be used to provide summer foliage
interest when the others are dormant. They should, however, be
heavily mulched over winter -- I'm not sure if they would survive
freezing in a container.
There are of course many other kinds of bulbs that could be used, but
those are the ones that are commercially available.
Fritillaria meleagris, in the USA, is best purchased as a potted
plant in growth, since the bare bulbs offered in garden centers have
usually been stored too long and are likely to be dead. I was
fortunate to be able to buy some named varieties from the UK many
years ago, which came in good condition, and from them have descended
hundreds of offsets and seedlings. SInce I moved to a site with clay
soil rather than the gritty soil at my former home, they have
flourished even more, which I attribute to the moisture retention
they now experience.
Jane McGary
Portland, Oregon, USA