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Hardy Summer Bulbs: Home

Lilium 'Pink Twinkle'; Photo by Ivo Vermeulen
Lilium 'Pink Twinkle'; Photo by Ivo Vermeulen

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 energy storage systems to get them through times of deprivation. It might help them successfully survive a cold winter on the slope of a mountain (e.g. tulips) or help them through a dry summer (e.g. amaryllis). 

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 and lilies 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 and gladiolus are corms.

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

Hardy bulbs are generally planted in the fall. The rule of thumb is to plant them at a depth of 3 times the height of the bulb and space them 3 times the width. There are some exceptions, so make sure you read the directions.

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, when planting, with a balanced fertilizer. 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.

Lily (Lilium)

is an emblematic diva 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. 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 3 to 4 inches deep for small bulbs and 4 to 6 inches deep for larger bulbs. An exception is the Madonna lily (Lilium candidum); this bulb should be planted only 1 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 'Severn Sunrise' at NYBG; photo by Ivo Vermeulen
Crocosmia 'Severn Sunrise'; photo by Ivo Vermeulen

Crocosmia (Crocosmia)

are corms that can perennialize successfully in the garden. Crocosmia usually reaches 3 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.

Crocosmias herald from South Africa. Like most bulbs, it requires good drainage. Crocosmia prefer average moisture levels and full sun to part shade. Plant them 2 to 3 inches deep in clusters of 12 to form a solid group (space 4 to 6 inches apart). They can be planted in the fall or the spring.

Allium at NYBG
Allium in the garden at NYBG

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 (low water) 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 cristophii) with it starry, softball-sized flowers. At NYBG, we plant our alliums in the fall. 

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