Home Gardening Center Tip Sheet: Summer Bulbs

By Sonia Uyterhoeven

·· Bulbs ··


Hardy Summer Bulbs


We toss around the term bulb very loosely when in actuality we are referring to geophytes--meaning ''earth plants.'' What is a geophyte? The term refers to plants that have developed storage systems to get them through times of deprivation. It might help them successfully survive a cold winter on the slope of a mountain like tulips (Tulipa) or help them through a dry summer like amaryllis (Hippeastrum).

If you slice a true bulb open, you will find a rudimentary flower that is encased by fleshy scales. Bulbs may or may not have a protective coating (or tunic). Anatomically, they are modified leaves. Tulips, hyacinths (Hyacinthus orientalis), and lilies (Lilium) are all true bulbs.

Corms are modified stems. They usually look a little bit like plump chocolate kisses. They are planted in the same way as bulbs--vertically with their tips facing upward and their flat bottoms downward. Crocuses (Crocus) and gladiolus (Gladiolus) are corms.

Rhizomes are also modified stems. They are a thick and fleshy storage system that grows horizontally under or on the surface of the ground. Cannas (Canna) and irises (Iris) are two easily recognizable rhizomes.

Tubers or tuberous roots are modified roots. Since they are roots, they contain no buds (growth points). When you divide tubers, you always need to make sure that you have part of the stem with a bud attached. Dahlias (Dahlia) are the classic example. What does that make a potato (Solanum)? They are stem tubers. Their buds commonly form at the base of the swollen stems--that is why your potatoes have eyes.

Hardy bulbs are generally planted in the fall. The rule of thumb is to plant them three times the height of the bulb and space them three times the width. There are some exceptions, so make sure you read the directions.

Tender bulbs should be planted in spring. They can either be planted directly in the ground or started inside early in the season (February to March). Many of the tender bulbs need warmth to get them going--this could either mean a sunny windowsill or some form of bottom heat (radiator or heat mat).

When planting your geophytes in the garden, remember that most of them will prefer excellent drainage. Amending the soil with compost not only adds important nutrients but also provides them with good drainage. Plant bulbs on a slope or in raised beds if you have heavy soil.

It is always good to fertilize your geophytes with a balancerd fertilizer when planting. Some of them are heavier feeders that respond well to supplemental feeding throughout the summer to keep them going, but many of them like it lean.

At the end of the summer, tender bulbs usually benefit from being cut back by a frost to help signal dormancy. Cut back the foliage and dig out the tubers, rhizomes, or corms. Let them dry out for a few days in the sun and then store them for the winter. The most common way to store these plants is to place them in peat moss, sand, vermiculite, or Styrofoam peanuts. Box or bag them up (in a paper bag so they can breathe) and place them in a cool garage. Some geophytes require specialized treatments--these are general guidelines.

Hardy Summer Bulbs

Lily (Lilium) are emblematic divas of the perennial garden for good reason. Asiatic lilies are some of the earliest lilies whose blooms can either face upward, outward, or be pendant; Oriental lilies have overpowering fragrances; martagon lilies have majestic whorls of flowers, trumpet lilies have their tell-tale flared flowers, while Orienpets are outstanding hybrids.

Lilies are typically planted in fall (although they can be planted in spring). The bulbs are fairly distinguishable with a large number of fleshy scales. Lilies have no protective coating (or tunic). It is important that this bulb does not dry out and that its roots are not damaged.

Plant your lilies three to four inches deep for small bulbs and four to six inches deep for larger bulbs. An exception is the Madonna lily (Lilium candidum); this bulb should be planted only one inch deep. If you are planting your lilies in a drift, dig a large hole to accommodate the entire group. Space them 12 to 18 inches apart depending on the ultimate size of the cultivar.

Lilies demand good drainage. Amend the soil with compost and fertilize in spring with a balanced fertilizer. To get healthy blooms, keep your lilies well watered throughout the summer.

Lilies are extremely fragile when they are young. If you snap off the top growth when they emerge, you will loose your flowers for the season. Place a marker near them so that you remember where you have planted them.

Many lilies need staking. It is best to place the stake early so that you don’t end up piercing the bulb. Large stakes can look unsightly in the garden if they are not camouflaged by a large stem; place a small stake in as a marker when planting and then replace it later with the actual stake.

Crocosmia (Crocosmia) are corms that can perennialize successfully in the garden. Crocosmia usually reaches three feet tall. It has sword-like foliage and tubular flowers that hang off an arching scape (stem). The most common cultivar is ‘Lucifer’--it is hardy to Zone 5. Cultivars that are not reliably hardy in this area (particularly the yellow cultivars) can be lifted and stored like gladiolus.

Crocosmias come from South Africa. Like most bulbs, they require good drainage. Crocosmia prefer average moisture levels and full sun to part shade. Plant them two to three inches deep in clusters of 12 to form a solid group (space four to six inches apart). They can be planted in the fall or the spring.

Ornamental Onion (Allium) with their enormous globe inflorescence (flower) are eye-catching. As a member of the onion family, the bulbs are also delightfully deer and rodent resistant. These bulbs originate from Central Asia and tend to like dry, hot summers--they are ideal in a xeric garden that provides them with excellent drainage.

The only real drawback with most ornamental onions is that their foliage starts to deteriorate before the flower opens to its full beauty. We try to hide their ugly feet by placing them in amongst tall-growing perennials. One ornamental onion whose foliage does last while it is in bloom is the compact Turkestan onion (Allium karataviense) with its glaucous foliage.

Another favorite is the drumstick allium (Allium sphaerocephalon) that looks like little purple Easter eggs. They naturalize wonderfully and mingle effortlessly with just about any perennial or rose. A classic is the Persian onion (Allium christophii) with it starry, softball-sized flowers. We plant our alliums in the fall.

Learn more about Tender Summer Bulbs like dahlias, gladioli, and Persian buttercups.

Download this Tip Sheet.

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Generous support for the Home Gardening Center has been provided by Kenneth and Ellen Roman.