Home » Gardening Information » Great Plants
Year-Round Care of Summer Bulbs
by Becky and Brent Heath
People often expect all bulbs to look just like those of daffodils and tulips—hard, round, and brown. However, many bulbs that flower in summer are not true bulbs, but rather rhizomes, tubers, corms, or root tubers, and they have odd, asymmetrical shapes and are rarely rock hard. In fact, they look more like bare-root perennials than true bulbs; but unlike perennials, these bulbs produce a sometimes funny-looking nutrient storage chamber that gives them a head-start on the growing season and allows them to be safely out of the ground for a short period of time. When buying bulbs, inspect them closely and avoid or return any with soft, brown, mushy spots, as these may be infected with an insect pest or a disease. For best success, plant the bulbs as soon as possible.
Starting Tender Bulbs Indoors
If you're gardening in an area that's colder than the USDA zones recommended for certain tender bulbs, you can still grow them, but you may want to start them in pots indoors. This will enable the plants to develop and mature early enough to give you a long season of enjoyment. Once the weather has warmed, you can transplant them into the garden or simply drop them with their pots into decorative containers. Enjoy the potted plants on your deck or patio all summer long, then move them back indoors in the fall. Winter care may vary, so consult the cultural instructions for each bulb.
To start tender bulbs indoors, plant them in pots at the recommended depth and place them about 6 to 12 inches below grow lights to keep the plants from becoming leggy, which can happen as the foliage stretches upward searching for light. In addition, place a Gro-Mat, Heat Mat, food warming tray, or similar device under the pots to give them bottom heat of about 70 F. Most tropical bulbs love warm soils and hate to be cold. They will root best and have the showiest blooms if they are grown in soils between 65 and 75 F. Exposure to cold early in their development can stress bulbs and make them more susceptible to fungus problems and rotting, or may even cause them to abort their blooms.
Planting Outdoors
Like cannas, most tropical bulbs love warm soils, so gardeners in colder areas may want to start them indoors and move them out once the soil has warmed.
Amending your garden soil is the key to making your bulbs thrive. They may emerge if planted in almost any soil, from clay to sand, but they probably won't flourish unless the soil contains the proper nutrients and enough organic matter, and provides adequate drainage. We've added organic matter to our soil for many years, and with each passing year, we believe more strongly in its benefits. When planted in organically enriched soil, our plants are healthier, taller, and lusher, require less care and water, and produce more flowers.
Before planting, add lots of well-decomposed organic matter to your soil—compost, leaves, horse manure, or anything else that will enrich the soil and provide unrefined nutrients. It's best to do this before planting: Till a 2- to 6-inch layer of organic matter into the soil; in subsequent years, top-dress hardy bulbs with a 1- to 2-inch layer while the bulbs are dormant.
If you have an area in your garden with no actively growing plants, you can easily plant a large number of bulbs at once: Just lay down a thick layer of compost and place the bulbs right on top; then cover the bulbs with sand, soil, or mulch to the proper depth. This is an easy way to plant bulbs in a raised bed, which will improve drainage and add organic matter, ensuring that the bulbs are in good soil.
Hardy summer bulbs like lilies, lilies-of-the-valley, and alstroemerias can be planted as soon as the risk that the ground may freeze has passed, at about the same time you would plant peas. Plant tender bulbs like cannas, dahlias, and elephant ears later, when the soil temperature reaches at least 60¡ F. That's also the time to transplant any bulbs you started indoors into the garden.
Most bulbs, whether tender or hardy, will do best when planted at a depth of three times the height of the bulb. There are exceptions to this rule, so it's always best to check the cultural instructions that should be included with your bulbs. If the recommended planting depth is within a range of several inches, plant on the deeper side if you live in a cooler area, to keep the bulb below the frost line. If it's difficult to tell the top from the bottom, plant the bulb, rhizome, tuber, or corm on its side. As a rule of thumb, space bulbs about three times their width apart.
If you garden in very heavy clay soil, you may want to amend the top few inches, plant the bulbs shallower than recommended, and make up the difference in depth with a thick top-dressing of mulch, or sand and mulch. Mulch is also useful for bulbs that are only marginally hardy in your area: Top-dressing with a thick blanket (4 to 6 inches) of mulch such as pine needles, chopped leaves, or other light, airy material, can often increase a plant's hardiness by a zone or two. Just be careful not to cover the tips of the emerging leaves of bulbs, corms, rhizomes, or tubers that have begun to sprout at planting time. Instead, mulch around the leaves as they continue to grow above the surface. All of your bulbs will benefit from a mulch of any of the materials mentioned above after the soil in the garden warms to about 70 F. This will conserve moisture and keep the foliage and flowers clean.
Sun And Moisture Considerations
In the fall, harvest tender bulbs for winter storage. Dig up the entire root system and shake off the soil.
If you live in an area where summer temperatures are very hot, you may want to place plants that do best in full sun to partial shade in a spot that will be shaded during the hottest part of the day, from midday until afternoon. On the other hand, if you provide adequate consistent moisture, some of the bulbs mostly used in the shade (caladiums, lilies-of-the-valley, achimenes, oxalis) will tolerate full sun.
Many bulbs from tropical climates, such as caladiums and gingers, grow best in damp soils, and tend to do better when planted in soils that stay moist during the bulb's period of dormancy. Bulbs like gladioli and crocosmias, native to alpine and desert areas where soils are drier, will do best in soils that drain well and stay drier during their winter dormancy. Consequently, it is a good idea to plant these bulbs somewhat deeper than the cultural instructions suggest. Planting them in a berm or raised bed is often best.
Fertilizing
Incorporate organic fertilizers into the soil when you're planting, then broadcast more during the growing season. If you decide to use a liquid fertilizer, reapply it every two weeks or so, depending on the amount of organic matter in your soil; liquid fertilizers tend to leach quickly through soils deficient in organic matter. In addition, it's a good idea to top-dress with a slow-release fertilizer such as Holland Bulb Booster at the time of planting and each succeeding spring to maintain a good nutrient level. Just remember never to put non-organic fertilizers in the hole when you plant bulbs, as these can burn tender roots.
Most summer bulbs appreciate the extra nourishment of fertilizers, but make sure to avoid products high in nitrogen (the first number of the N-P-K fertilizer formula on the package label), as they tend to encourage lush leaf growth, sometimes at the expense of flowers. However, extra potassium (the K in the formula) is generally helpful in forming strong, disease-resistant bulbs. And phosphorus (the P) promotes strong flowering, although most soils contain sufficient amounts of this slow-moving nutrient.
In boggy areas, plants rarely will require extra fertilizer, because nutrients from the surrounding area tend to accumulate in these places along with the moisture. However, if the foliage of plants growing in a boggy area is spindly or sparse and lacks rich, dark green color, try adding 1 to 2 inches of good, well-cured compost.
Summer Care
If the tired foliage of post-bloom bulbs offends you, place them among other plants to hide their fatigue among fresh growth. Don't cut back or tie up the leaves of hardy bulbs after they have bloomed: This is the time when the plants are building up nutrient stores for the following growing season. Wait to cut the foliage until it begins to turn yellow and flop over.
Deadhead dying flowers from plants to conserve the energy they would expend making seed, unless you have planted bulbs that naturalize (spread by seed) and you wish them to do so! Deadheading certain bulb flowers like dahlias, caladiums, anemones, cannas, and crinums will encourage them to re-bloom.
Many summer bulbs like consistent moisture, so if you live in an area where summers are dry, use drip irrigation once a week. Don't use overhead irrigation if possible, as it is hard on flowers and can foster mildew and fungal diseases.
Harvesting And Storing Tender Bulbs
After the leaves of tender bulbs have been killed by frost, harvest the bulbs for winter storage. Dig up the entire root system and shake off the soil, remove the dead or dying leaves close to the bulbs, and place the bulbs in dry peat moss, chipped leaves, or wood shavings in an open paper bag or container that will allow them to breathe. Store in a warm, dry place. A garage that's kept above freezing is fine.
If this process sounds too cumbersome, you can treat summer-flowering bulbs as annuals; some are less expensive than many annuals anyway. You may also be surprised to find bulbs you've written off as too tender to survive the cold will indeed come up again in spring. We're always amazed at how many summer-blooming bulbs survive the winters in our Virginia garden (Zone 7)—they seem to be far hardier than the reference books would have us all believe.
Brent and Becky Heath are garden educators who own and operate "Brent and Becky's Bulbs," a wholesale/retail catalogue and web-site flower-bulb business in Gloucester, Virginia. They distribute all types of bulbs to gardeners, cities, universities, and botanical gardens throughout the United States. Daffodil hybridizers, Brent and Becky are co-authors of Daffodils for American Gardens. They received the American Horticultural SocietyÕs Gold Medal in 2001.