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Chapter 5: How to Grow Tender Bulbs Indoors
by Tovah Martin
If you think that bulbs are solely a midwinter's affair, consider the caladium. If you're under the impression that bulbs are common little garden flowers potted off-season and given as Easter gifts, ponder the pleione. Beyond those majestic amaryllis that open their wide-faced flowers just in time for the holidays, beyond the sinningias that tug your heartstrings at supermarket check-out counters, all sorts of tender bulbs are available. Most hail from South Africa, a few come from South America or Asia, and they stagger their blooming performance and resting periods depending upon their individual cycles: some like it hot, some like it cold; some sprout in summer, some perform in winter. So, tender bulbs tend to be a little more challenging than your average 'Tete-a-Tete' narcissus. But that's part of their intrigue.
You probably never realized that many of your favorite indoor bloomers sprouted from bulbs. A clivia, for example, reveals scant evidence of its underground agenda. Its broad, strap-like leaves remain intact even when the plant is resting. Haemanthus and crinums are also discreet about their cycles. However, not all tender bulbs are equally apt to keep clothed throughout their dormancy. For example, some oxalis disappear totally from sight, not even leaving a telltale stubble as evidence of the once and future display.
Due to their diversity, due to the fact that they come from different habitats and have such divergent cycles, it's difficult to make rules that apply to all non-hardy bulbs. However, those that flower in winter (mostly native to South Africa) tend to have some common denominators, while summer bloomers all share mutual preferences as to planting times. If you are sensitive to a bulb's cycle, you can guess its other wants and needs.
As a rule, both summer- and winter-blooming tender bulbs, unlike their hardy counterparts, should be treated more like the average pot plant. You can tuck a hardy hyacinth into a pot and provide it with scant light and little sustenance—it will perform nonetheless. Not so with the non-hardy bulbs. They must be given all the amenities that most houseplants demand, such as sufficient light, moderate water, a good rich soil underfoot and fertilizer during their growing season.
When to Plant
The most immediate concern facing a gardener tackling tender bulbs is the planting procedure. In the best of all worlds, you would receive instructions with a newly purchased tender bulb making it clear exactly when it should be planted for peak performance. However, a goodly number of tender bulbs are exchanged among friends and might not come with any written information. In the absence of instructions, you'll have to look for clues. Winter-flowering bulbs (again, mostly South African) should be planted from late summer to autumn. Summer bloomers should go into the soil in late winter or early spring. Keep your eye peeled for telltale signs of growth—when the moment is ripe, shoots often sprout from the tips of tender bulbs before they ever hit soil. That not-so-subtle hint is your cue that the bulb in question is ready to be planted.
Which End is Up?
There is one rule that all bulbs share in common. They all want to be planted with the growing tip facing upwards and the roots sinking down. It sounds simple, but you can't always easily discern which end is up. Tuberous begonias are particularly perplexing. Check for round, crater-like markings where the gone-by stem once sprouted: that's the top. Look for spiny vestiges of root growth: that's the bottom. The easiest bulb is achimenes—which is actually a rhizome and so can safely be laid on its side. When in doubt, make an educated guess and pray for the best.
Growing Medium
Tender bulbs are more particular about their growing medium than their hardy counterparts. You cannot just sink a veltheimia—or most other tender bulbs, for that matter—in sand or a forcing jar half filled with water. They require some oomph under foot. Most tender bulbs prefer a standard potting medium that is rich in organic matter but slightly sandy. To keep the bulb from rotting, good drainage is essential (the exception being calla lilies, Zantedeschia, which are aquatic). Clay pots are aesthetically pleasing and also provide ballast to keep the plants from tumbling over—especially veltheimias and agapanthus with their top-heavy growth.
How Low Should They Go?
Generally, tender bulbs are planted an inch below the soil. However, tuberous begonias typically should be only half-buried, while nerines, tulbaghias, crinums and veltheimias should be positioned so most of the bulb is exposed. It would probably do no harm to bury them, but it's certainly pleasing to see where the bulb spews forth its foliage.
Water
After planting, water the soil lightly when it is dry to the touch (never soak the soil, especially before a bulb makes visible growth). Most bulbs prefer to be under- rather than over-watered. After all, the bulb itself is a water storage unit custom made to carry the plants over during dry times, and it can easily rot if too much moisture is provided.
Living Quarters
Because too much water can be detrimental, bulbs are best grown in tight quarters. In many cases, the pot need not be much larger than the circumference of the bulb itself. In fact, a rotund bowiea or veltheimia poking out of a cramped container looks quite fetching. Smaller bulbs such as lachenalias, oxalis, freesias, cyrtanthus, ranunculus, tulbaghias and achimenes should definitely be crowded several to one container. Larger bulbs should go solo.
Light
You can leave the pot in indirect sun until sprouts appear, then place it in its permanent location. Most tender bulbs prefer bright light during their growing and blooming cycle. A south-facing window is ideal, especially during the winter when light levels are low. Oxalis and freesias are particularly uncompromising about their light demands. Most other tender bulbs will good-naturedly tolerate less-than-ideal conditions. Sinningias, cyclamen and clivias actually prefer the lower light levels available on an east- or west-facing sill. Achimenes are summer bloomers and are often displayed in hanging baskets on outdoor porches. If that's where you plan to grow them, be sure to select a shady porch protected from direct sun at all times of day. The same is true for caladiums, which frequently find a place in the outdoor garden. Zingibers can tolerate quite deep shade.
Rest Period
Although you should generally treat tender bulbs like the average houseplant, you must let them rest when the time is right. During a tender bulb's dormant period, stop watering the plant and remove it from direct sunlight. Winter-blooming bulbs require a summer respite, whereas summer-bloomers slumber in winter. Be sure to withhold water completely.
When to stop watering is not always clear. There's no question when oxalis, tuberous begonias, ranunculus, caladiums and achimenes are ready for dormancy: they send out no-nonsense signals such as browning up and dramatically dropping leaves. Not all tender bulbs drop their foliage and slip into a full-fledged sleep. Notably, cyclamen, eucharis, clivias, cyrtanthus, tulbaghias and zingibers retain their leaves while resting. No real harm would be done to these plants if you continued to water throughout the year. But you might not see blossoms. For example, clivias give no hint that they need a rest, but they refuse to set buds unless you withhold water between November and March.
When the foliage is completely dried with no sign whatsoever of growth, you can remove the bulbs from the soil and store them in a paper bag— not plastic bags, which tend to be damp inside. You can leave them in their containers—but only if you can resist the temptation to water the parched soil. Keep the plants in a cool, dark place while resting. Keep an eye out for the sprouts that indicate when planting time has arrived; if you don't furnish them with soil and sun post haste, growth will be leggy. Simply tuck them in the soil at the earliest possible moment. Then sit back and enjoy the growth cycle as it begins anew.
Tovah Martin is the author of several books, including Tasha Tudor's Garden, Well-Clad Windowsills and The Essence of Paradise: Fragrant Plants for Indoor Gardens. She is the garden editor of Victoria magazine and a horticulturist at White Flower Farm. Her greenhouse in Roxbury, Connecticut, is filled to the brim with bulbs both hardy and tender.