While in general bulbs are easy plants to grow, they can be difficult to understand, simply because there are so many different types. We have spring bulbs and summer bulbs, and then we have tender bulbs and hardy bulbs. And to confuse matters, not all of the so-called summer bulbs are tender and you have to buy spring bulbs in the fall. But things really aren't as complicated as they seem.
Spring bulbs are, perversely, those that are planted in fall. Most spring bulbs are hardy bulbs - those that not only tolerate cold, but demand it in order to flower. These include daffodils, tulips, muscari, crocuses, iris reticulata, snowdrops and all of those other bulbs that delight us by poking their heads from the ground early to brighten up spring.
Spring bulbs are the ones that endear themselves to us by being force-able. All we need to do to get spring bulbs to bloom at another time, more convenient for us, is to fool them into thinking they have gone through winter by planting them and then storing them in a cold, dark place for anywhere from 2-4 months. So if for some reason you really need tulips in July, it may be possible to get them.
Summer bulbs are the ones that we plant in spring or early summer, so that we can enjoy their flowers later in that season. Many of these are also "tender" bulbs" for northerners - the type that cannot be planted in autumn as the cold would kill them. But they respond to day length and warmth and will sprout and grow and flower for us when planted in soil that has warmed up in late spring.
But not all summer bulbs are tender. Some of them are just quick performers. Think of lilies. I have planted them in fall, but also in spring, and both times, I had a beautiful flowering display at the right time. Lilies, from the gigantic Orientals to the many old-fashioned favorites are fully hardy (as low as zone 3!) for all but the coldest regions and can be left in the ground year round.
Daylilies, while technically tubers instead of bulbs, are also fully hardy, many to zone 3, but can be planted spring or fall.
Other hardy summer bulbs include alliums, brodiaea, camassia, anemones, crocosmia and Arum italicum. These can be grown in ground year round in zones 6 and sometimes 5. So, as you see, not all summer bulbs are tender.
Some bulbs are only semi-tender. These are the ones that gardeners in the far north must dig and store each winter, but which those in milder climates - but not necessarily tropical ones - can leave safely in the ground. For instance, many gardeners in zone 7 have reported that they don't dig ranunculus, cannas and calla lilies, and yet they come back. Zone 7 is hardly tropical! I myself once forgot to dig up a clump of calla lilies that I had planted at pond side, and was amazed to find them blooming there the next summer. Perhaps it was a mild winter, as they did not return the following year to repeat the performance. Callas are generally more tender than that!
But many summer bulbs are tropical in origin and simply won't tolerate cold of any kind. These must be dug and stores unless you are in zones 8 or higher - places that get little in the way of hard freezes. Some, like the magnificent giant elephant ears and caladiums are hardy only in zones 9-10. Begonias are very tender and are not hardy below zone 10. Most callas aren't reliably hardy in areas colder than zone 9, but the classic white Zantedeschia aethiopica is somewhat hardier and has been known to survive reliably in zone 7.
Dahlias are happy enough to stay planted in zones 8 and above, as are gladiolus.
What this means for the gardener is that any bulb that is tender for them has to be either treated like an annual or dug up in autumn and stored over winter. The very tender bulbs - the elephant ears, begonias and caladium, need to be lifted before the first killing frost. Others can be left in situ until they are blackened by frost. Then the foliage is cut off, they are dug up and left in a dry place with good air circulation until the soil has dried and can be brushed off, then packed in a few layers of an appropriate "medium" such as perlite, vermiculite, cocoa hulls, clean sawdust or peat moss until it's time to replant when the soil has warmed in spring.
I like to use slightly damp peat moss and I also check them periodically to make sure they aren't shriveling or molding. Mold means I stored them too damp. I can try to save them by dipping them in a mild bleach solution, then allowing them to dry and restore in a less damp medium. If the damage is only slight, they may survive.
If they are drying out, I mist the packing medium and close the bag. I never use plastic but only paper boxes or bags as they breathe, allowing air to circulate and not encouraging moisture and rot.
The good part about these tender bulbs is that they are usually fairly easy to store and will come back and flower for us again the next year.
The sad part is that there is no way to fool them the way we do the hardy spring bulbs. If you have a yen for calla flowers in February, you will need to find a florist with controlled greenhouse conditions that take not just temperature, but also day length into consideration when growing them for the market. We haven't the facilities to force tender bulbs according to our own timetables.
You can, however, give these plants a head start for this summer's garden by potting them up now, indoors where it's warm. That way they can start putting out roots and sending up shoots, and will be that much further ahead of the game when your soil warms and it's time to plant them out. Place the planting container on a heat mat and they will think they are in heaven.
Many tender bulbs can also be grown as houseplants, given the right lighting and warmth. But they will bloom on their own timetable, rather than yours. Plants accustomed to growing in mild weather conditions in their native habitat respond more to day length than to temperature when determining that it is time to bloom. They respond to a gradual increase in both temperature and humidity - just as they would get if growing in their native habitats. This isn't easy for us at home.
So hardy spring bulbs can be forced, and thus give us pleasure any time of year as well as in their natural season. To compensate for this, they force us to be out in the cold digging planting holes, and sometimes we have to put our jackets on to go out and enjoy the earliest ones.
Hardy summer bulbs give us the best of both worlds - they can be planted and left in the ground in spring or fall and will bloom reliably without pampering.
Tender summer bulbs are planted under more pleasant conditions, but may require extra work since they need to be dug, stored and then replanted annually. They are not easily fooled and so are difficult to force - but they make a big splash in the garden that most of us intrepid gardeners think makes them well worth the trouble.
I grow all types, because I love to garden and love the variety that these different bulbs bring to my garden design. If you're an intrepid gardener, try them all. Otherwise, choose the bulbs that you are willing to put the effort into maintaining, or those you can feel justified in growing as annuals. Believe me - the elephant ears and dahlias and other tender bulbs put on such a splash in the garden that it's money well spent, even if only for a season.
