For Release On Or After 04/23/10
By Dan Gill
LSU AgCenter Horticulturist
Now is a great time to add summer bulbs to your gardens. Most summer-flowering bulbs are native to tropical and subtropical climates and will reliably bloom in Louisiana for many years. Summer bulbs are those that bloom roughly from May through September.
Because they are such a large and diverse group of plants, providing general instructions on care for summer flowering bulbs is difficult. Indeed, no matter what situation you have, you can almost always find a few kinds of bulbs that will thrive.
Most summer bulbs prefer good drainage, although calla, canna, crinum, spider lily (Hymenocallis), Louisiana iris, yellow flag and some gingers are a few exceptions. Full to part sun (6 hours or more of sun a day) is important to most of these plants for healthy growth and flowering, but many, such as achimenes, caladium, gingers and bletilla, do fine in shadier spots.
Most summer bulbs have a dormancy period when the foliage dies off and the bulb rests. This period generally occurs in winter. Even bulbs that are normally evergreen, such as agapanthus, will go dormant if the winter is cold enough and several hard freezes occur.
As bulbs enter dormancy, growth stops, and the foliage will become yellow, and then brown. At that time, the foliage may be trimmed back to the ground. Be sure to place markers where the dormant bulbs are located. Sometimes it’s hard to remember exactly where they are when nothing shows above ground, and you can accidentally dig into them with a shovel if you’re not careful.
Many summer bulbs are not heavy feeders because they are often native to regions with relatively poor soil. You should generally dig generous amounts of organic matter, such as compost, aged manure or peat moss, into the area before you plant your bulbs. A light sprinkling of a general-purpose granular fertilizer once or twice during active growth beginning in March and ending in August is sufficient for most summer bulbs.
Seed pods sometimes will form after a summer bulb has bloomed. Unless you’re breeding the plants or want to grow some from seeds, allowing the seed pods to develop is a waste of energy for the plant. It’s best to remove the old flower spikes or developing seed pods as soon as you notice them. Growing most summer bulbs from seed is not especially difficult, but it requires patience because most will not bloom until they are at least two to three years old.
Most summer bulbs are best propagated by dividing the clumps when they are dormant in early spring. Some bulbs, like crocosmia, do best divided every year or two while others, like agapanthus, prefer to be left alone.
A number of outstanding summer bulbs are available for Louisiana. One of the best-known and most popular is the caladium, which is grown for its colorful foliage rather than flowers. You can buy caladium bulbs now and plant them directly into the garden. You also may plant pre-sprouted bulbs that are available at many local nurseries. Unless you need growth immediately, the unsprouted bulbs are generally a better buy. Caladium foliage is present from April through October, and the colorful, bold leaves combine well with other shade-loving plants.
Gingers grow well in partially shaded conditions. Because they are native to the tropics, ornamental gingers thrive in our hot, humid summers. Despite their tropical origins, however, a large number of gingers are completely root-hardy here and make excellent, permanent additions to your landscape.
The plants we call gingers actually include many genera, with different sizes, growth habits and flower shapes. Low-growing gingers such as kaempferia and globba make great ground covers, while larger gingers reaching 6 to 12 feet, such as Costus, Alpinia and Hedychium, can be used for accents, screens or background plants.
A favorite lily that grows well here is the Formosa lily, Lilium philippinense. Looking for all the world like a giant Easter lily, the Formosa lily blooms in late summer, around July/August. It thrives in our heat and humidity and appears to have no major insect or disease problems.
This is just a taste of the many outstanding summer flowering bulbs for our area. They are generally reliable, long-lived and easy-to-grow. Dive in and have fun. The following lists will help you get started.
– Summer bulbs for full sun to part sun: agapanthus, belamcanda, calla, canna, crinum, crocosmia, dahlia, dietes, garlic chives (Allium tuberosum), gladiolus, gloriosa lily, habranthus, hymenocallis, lilies, lycoris, oxalis, stargrass (Hypoxis angustifolia), tigridia, society garlic (Tulbaghia), zephyranthes.
– Summer bulbs for part shade to shade: achimenes, alpinia, arisaema, bletilla, caladium, calla, costus, curcuma, globba, hedychium, hymenocallis, kaempferia, neomarica, oxalis.
Rick Bogren