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Plant Focus: Globe amaranth (Gomphrena)

August 7, 2009 •

Jonathon Hofley / Michigan Gardener
‘QIS Lilac’by George Papadelis

The dog days of summer can certainly take a toll on the garden. Many plants are well-suited for intense heat while others struggle to maintain a flower for more than a few hours. One of the most heat-tolerant, and underused, annuals is Gomphrena. Its common name is globe amaranth and it is native to Central America. Once established in the garden, globe amaranth will tolerate temperatures in the hundreds about as well as any annual. It comes in several colors and plant height can vary from just 9 inches tall to over two feet. In my opinion, the best thing about globe amaranth is that it is relatively uncommon; plants will usually draw enough attention to conjure the occasional, “What is that?” I love hearing those words of wonderment from gardeners.

Gomphrena develops clover-like, round flower spikes that are almost 1 inch across. They make a great cut flower, and when dried, they will retain their shape and color indefinitely. They will thrive in any sunny position and will tolerate a broad range of soil as long as it is well-drained. Rain can make some annuals, like petunias, droop and flop. Gomphrena, however, stands strong and erect despite high winds or rain.

Sakata Seed America
‘Gnome White’The most popular series of gomphrena is the Gnome series. It is a dwarf variety that comes in about four colors including purple, pink, and white. It only grows about 9 inches tall and wide, and makes a great edging plant. In the annual border, this is a more interesting alternative to the common marigold or ageratum. It can also be a valuable addition to containers—especially those exposed to intense sun. Its compact size makes it suitable for sale in small packs just like other, more common bedding plants. It is also one of the more inexpensive annuals you can buy.

The taller gomphrenas are the ones that I find most interesting. They can be used as a unique addition to the perennial border since they are unfamiliar to many gardeners. One of my most pleasant memories of gomphrena came to me at Longwood Gardens. The variety ‘Bicolor Rose’ was planted in a vibrant mass along with several other unique annuals. It stands about two feet tall and the rose-colored flowers sport a spot of white at the tip. This is by far one of the most vividly-colored gomphrenas available. Try this variety in small groups in the perennial garden.

Julia Hofley
‘Strawberry Fields’Sakata Seed America
‘Gnome Pink’Other tall varieties include ‘Strawberry Fields,’ with strawberry-red flowers on strong upright stems to about 24 inches. ‘Lavender Lady’ has lavender flowers on 24-inch stems. Both of these varieties are getting harder and harder to find. The ‘Woodcreek’ series (also known as the QIS series) grows 24 to 30 inches tall and comes in seven colors including lavender, pink, orange, red, purple, rose, and white. Seeds for these are somewhat more available, especially amongst the cut and dried flower circles. Plants are sometimes sold in larger packs or small pots.

Whether you garden with perennials or annuals, gomphrena provides an interesting, easy to grow, heat-tolerant choice. Gardeners often overlook gomphrena in early spring when garden center plants can appear somewhat unimpressive. But once summer comes along, few annuals can provide such a unique flower and exceptional weather tolerance.

George Papadelis is the owner of Telly’s Greenhouse in Troy, MI.

At a glance: Globe amaranth

Botanical name: Gomphrena (gom-FREE-nuh)

Plant type: Annual

Plant size: 9 to 24 inches tall and wide

Habit: Upright clump

Flower color: Lavender, rose, red, pink, orange, purple, white

Flower size: 1 inch across

Bloom period: Summer

Light: Sun

Soil: Well-drained

Uses: Shorter varieties can be used as edging plants. Taller varieties can be used both in mass annual plantings or in perennial borders.

Remarks: Exceptional heat tolerance. Stands up to wind and rain also. Excellent cut flower; when dried, retains shape and color indefinitely.

Planting a yucca in an outdoor container

July 30, 2009 •

I want to plant a yucca in a container that will stay outdoors all winter. Can I use regular container potting soil? If not, what type should I use?

Container gardening for perennials and small ornamental shrubs is growing in popularity, but not without problems. The greatest challenge is overwintering. In winter, the temperature of the soil in the ground stays much warmer than the temperature of the air. In some cases, up to 40 degrees different. The problem with container gardening is that the roots of the plant are elevated above the warm earth, and the cold air quickly drops the temperature of the soil in the container below what happens naturally in the ground. This usually kills the roots of the plant and leads to a disappointing spring.

Yucca has been designated as a zone 4 plant, or able to withstand a low temperature of -20 to -30 degrees Fahrenheit if planted in the ground. If planted in an above ground container, the roots will most likely die if the soil temperature drops below 10 degrees Fahrenheit. To be successful, controlling the temperature of the root zone is the key. Even if plants are in the ground, soil temperature is still important. That is why so many gardeners swear by a good overwintering mulch. The mulch helps insulate the ground from extreme temperature changes, especially those cold January nights.

Regular container potting soil would be recommended. Be sure to fertilize as needed.

Why have my Hydrangeas changed bloom colors?

July 26, 2009 •

I have a hydrangea that used to have big, blue flowers. While the flowers are still healthy, they are now a dusty pink. Is the plant sick? What happened? Can I get the blue blooms back?

No, your plant is not sick. Your hydrangeas simply need a pH and nutrient adjustment. While the flower color of white-flowering hydrangeas is unaffected by soil pH, that certainly is not true with pink and blue-flowering varieties. In the case of the latter, the flower color is largely determined by the soil pH. In general, hydrangeas planted in more alkaline soils will be pink. The more acidic the soil, the bluer the flowers become. In between, they tend to take on a somewhat “muddy” appearance.

The clearest blues require the minor nutrient aluminum to develop fully. Since phosphorous tends to tie up available aluminum in the soil, one should avoid high phosphorous fertilizers if the bluer flower color is desired. The addition of aluminum sulfate is perhaps the single best way to promote bluer flowers. Use one pound (2 cups) per three feet of height around each shrub in the spring and water thoroughly.

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At a glance: Globe amaranth