Home Gardening Center Tip Sheet: Tender Summer Bulbs

By Sonia Uyterhoeven

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Tender Summer Bulbs


Dahlias (Dahlia hybrids) come in a wonderful range of heights, shapes, and colors. Their flowers are always spectacular and can be shaped like anemones, peonies, cactus flowers, or ping-pong balls. The plants can be as small as one foot tall or as large as seven feet. Most of them fall into the range of one to four feet. Try the Gallery® series for compact container plants; for dark foliage look for ‘David Howard’ (orange flowers), ‘Bishop of Leicester’ (lavender flowers), ‘Bishop of Llandaff’ (red flowers), or ‘Fascination’ (lilac-pink flowers).

Start them off early by planting the tubers in a pot four weeks before the last frost date planting two to three inches deep. Once all chance of frost has past, transplant them outside in a sunny spot in rich, well-drained garden soil. Stake immediately so that you do not damage the tubers.

If you plant the tuberous roots directly into the ground there are many recipes or techniques to follow. The most common is to dig a wide hole to about 10 inches deep. Amend with compost. Fill the hole to six inches and lay the tuber in the hole so that the eyes (new growth) are facing upwards. Fill the hole two to three inches. Once the dahlia starts to grow slowly fill in the rest of the hole.

Larger dahlias can be pinched when they are 10 to 12 inches tall for shorter, bushier plants. Water well during dry spells; deadhead to promote more blooms and feed every few weeks with a balanced liquid feed starting from mid-summer into fall.

Dahlias are indigenous to Mexico and Central America. In their native climates the tuberous roots (that look like oblong potatoes radiating out from the central stalk) stay in the ground. In this region they need to be lifted after the plants begin to die back from frost exposure and let them dry out for a few days. Store them in a cool, dark place to over-winter. We store our dahlia tubers in peat moss, perlite, or Styrofoam peanuts.

Gladiolus (Gladiolus hybrids) are magnificent cut flowers that grow from corms. They can be planted in the garden starting in May and then planted every two weeks through the middle of June to produce a long show throughout the summer. Plant either in a straight row for cutting or in small clusters of five to seven flowers for a vertical accent in a border. For your floral arrangement, cut the stem when just two to three flowers are open.

‘Glads’ prefer to be grown in full sun in well-drained soil. Plant the corms pointed side up (they look a bit like a chocolate kiss). Plant four to six inches deep and approximately six inches apart. Most gladioli will need staking; if you stake when planting you will not damage any of the roots.

They are generally used as annuals. If you are planning to over-winter the corm leave at least four leaves on the plant when you cut the flower. Cut the foliage down to an inch once the frost has cut the plant back. Dry the corms for up to three weeks. Clean off the old, tired corms that are underneath the new corm that has formed during the season.

Store the corms in a cool, dark, well-ventilated area in a paper bag or an egg carton. If you have had an insect problem during the season (thrips is common) then add a mothball to the paper bag or soak the corms in four teaspoons of Lysol® to one gallon of water for six hours and then dry. If this feels like too much work some of the species are hardy to USDA Zone 6. Look for Gladiolus caucasicus, Gladiolus dalenii hybrids and Gladiolus ‘Boone’.

Tuberous begonia (Begonia Tuberhybrida Group). Many people are familiar with the ubiquitous wax begonia (Begonia Semperflorens Cultorum Group) and the angel-wing begonia (Begonia coccinea) that graces every garden center. These adaptable plants have fibrous roots, grow in full sun to part shade, and flourish in well-drained soil that has been amended with organic matter. They are easy to grow and terrific for the beginner gardener.

Once you have mastered the wax begonia, graduate to their tuberous cousins. Tuberous begonias produce huge flowers that come in a wonderful array of sorbet shades. Flowers can be shaped like a rose or a camellia. For maximum flower power, try the Nonstop® begonias. If you like frills, look for Picotee begonias whose flowers are edged with a contrasting color. A new favorite of some growers for container gardening is the On Top® series of begonias.

You can buy the plants in spring or buy the tubers. Place the tubers on a damp tray of peat moss in February with the round side facing down and the flat side up. Once they start to show shoots and roots plant in a well-drained potting mix (plant nice and shallow so the tubers don’t rot, about half below soil line). Plant them outside once the temperatures have warmed up and all dangers of a frost are gone.

Tuberous begonia like well-drained, rich soil and do best in bright indirect light or part shade. Feed them either at the beginning of the season with a slow release fertilizer or add compost to the planting mix and then give them a boost of fish emulsion every few weeks. At the end of the season pull out the tubers after the first light frost; let them dry out for a day in the sun and then store them in peat in a cool, well-ventilated area.

Poppy-anemone (Anemone coronaria). One of the early harbingers of spring is the diminutive Grecian windflower (Anemone blanda). Its taller cousin, Anemone coronaria, arrives later in the spring, flowering in May and June. While the Grecian windflower is hardy in this area, the poppy-anemone is only hardy to Zone 7. They are tuberous rhizomes that perform best if soaked overnight before planting.

Plant Anemone blanda in the fall with the rest of your hardy spring bulbs. Anemone coronaria can either be potted up in fall and over-wintered in a cool greenhouse or potted up early in spring and then moved outside for a later bloom time. Anemone coronaria--as most geophytes (bulbs, corms, etc.)--like well-drained soil. The poppy-like flowers come in red, white, and purple/blue with rich black centers. The De Caen Group comprises popular single varieties while the St. Brigid Group is a nice choice for double-flowering anemones. These short-lived, inexpensive tubers are best used as annuals: plant two inches deep and four inches apart.

Persian Buttercup (Ranunculus asiaticus) is another late-spring/early-summer showstopper. The tuberous roots look like a miniature bunch of bananas or a tiny octopus. Hardy to Zone 8, this tender bulb is best planted a few weeks before the last chance of frost or potted up early in spring (February or March). Plant two inches deep and six to eight inches apart in well-drained soil with the claw-like structure facing downward and the fuzzy head on the top.

Persian buttercups make a wonderful cut flower and gracefully fill containers. This geophyte likes the cooler weather, so get it outside as early as you can. It will go dormant with the summer heat. The tubers are difficult to store. You can store them in peat moss in a cool location, or better yet, just use them as annuals. Look for the ‘Bloomingdale’ series for sensational color and a beautiful intricate rose-shaped flower.

Learn more about Hardy Summer Bulbs like ornamental alliums, lilies, and crocosmia.

Download this Tip Sheet.

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