Have you had flowering annuals that grow well in your flowerbed, but the same kind of plant does not thrive in planters, window boxes or containers? You copied companion plants from the photo in the national gardening magazine but one kind of plant dies in your container? Front row flowers in the flowerbed grow three inches taller and much wider than the plant tag shows, while annuals behind them grow shorter than expected?

Joe Hoffman, horticulturist at Yankton Federal Prison Camp for the past 27 years, knows that it’s not all your fault. He grapples with annual growing issues each year as his inmate horticulture students design, install and maintain the Observatory hillside display garden along Douglas Avenue.

 The steep hill displays a design well from top to bottom, at an angle seen most often by the public. Hoffman remembers the letters “Y” “C” there formerly on the Yankton College hillside in his youth. While he addresses perspective issues from laying out a design that is viewed from the street, the annual flowers and foliage that fill in the design as they grow, present some of the same growing issues that many gardeners face.

“We don’t just have sun and heat on plants that cause stress,” Hoffman said. “We also have soil temperature issues. In spring we may put plants in containers or raised beds because the soil temperature rises sooner than the ground temperature. When we’ve had some hot summer days, like this year, some plants don’t grow well with roots in that warm soil.”

Hoffman sees fuchsias, with large drooping flowers, sometimes sold in hanging baskets for Mother’s Day. But when the hanging basket soil warms up, the plants languish. Planting the fuchsia in ground on the north or east side of a house may help, until the soil temperature reaches 80-90 degrees. He finds an in-ground area where fuchsia receives direct sun about half a day, and mulches the plant with grass clippings or wood chips for it to flourish.

The annual verbena also has warm soil heat issues.

“Verbena as a bedding plant performs admirably well in beds as long as the air temperature is not too hot. Hot air warms soil. But if you put verbena in a pot and it gets hot, it’s useless,” he said. Plant tag suggest partial to full sun for this plant, but if roots are not mulched and the soil gets too hot, the plant does not continue to grow well. “It’s a plant we can’t use on hillside designs.”

A gardener may enjoy thumbing through garden magazines for container garden plant ideas. Companion plants in a container garden photo (of a less reputable magazine) may be placed together for visual affect, but not because the plants grow well together.

“There’s a short list of plants I wouldn’t use in containers,” he said. “If you have mixed plants in a container and one variety dies, it may be a heat issue. Trailing lobelia in a planter died for me, but the same plant in ground is doing fine.”

Hoffman finds that some alyssums from seed will not take the soil heat. “Blushing Princess” alyssum is lavender and propagates best from cuttings and performs better in warm soil.

He prefers many hybrid petunias to old fashioned petunias because they can take the warm soil.

“We’ve been putting geraniums in containers forever, but that’s because they work,” he said. Not ivy geraniums or Martha Washington geraniums, however.

“One of the plants we use a lot on the hillside design is vinca. It blooms all summer. Last season I used a dark basil and it got a disease in July. So this year, for the Olympic rings, I used a black-leafed pepper for the black ring. Peppers will tolerate a lot of heat,” he said.

Hoffman needs specific colors that match his design and growing conditions. Blue-flowered plants are less common in nature.

“We’ve had more trouble with ageratum over the years. We’ve used it for sky or water in the design, but it doesn’t perform well in heat,” he said.

“We used ‘Janie Primrose Yellow’ marigolds in the design this year,” he said. He finds that marigolds survive heat well. Display of color is another area in which small-flowered marigolds excel.

“From a distance, we see more color if the plant makes lots of smaller flowers that cover the green leaves instead of a few big flowers on a plant.” He gave the example of a pompom-shaped marigold showing more green and appearing less colorful than “Janie Primrose Yellow” marigolds.

Some plants survive the hot summer conditions but grow to unpredictable heights; a problem in a design garden.

“Salvia survives heat well but is not as good in containers. Salvia we planted in the design was supposed to be shorter,” he said. Weather issues impact even the most predictable plants.

“If we get a warm spring or cold snap, some plants stay smaller and some get taller than expected. Vinca for the red ring in the design was slow coming on with the cool spring. Snapdragons (planted in-ground) are shorter than expected, and are behind marigolds in the beds. Plants react so differently even when you’re very familiar with the plant,” he said.

Growth regulators are commonly applied by growers to their bedding plants that are shipped long distances. It makes it easier for transport and may contribute to attractive appearance on the shelf. There is no way to tell if this is done and delayed impact on the plants is not intended.

“I prefer to put seedlings out small,” Hoffman said. “If bedding plants are blooming, we pinch off the blooms (to encourage vegetative growth). When planting, we loosen the roots and pinch off the bottom of the root ball to encourage roots to spread out.” This approach is akin to perennial and tree planting methods.

Hoffman is a fan of the versatility and appearance of succulents in containers.

“They grow well indoors and can be brought outside. They perform well in heat. Succulents use form to grab attention rather than bloom color. They might have big rubbery leaves or tiny leaves but the contrast catches your attention.” Subtle colors of succulents defer to the plant’s shape and texture.

If you drive by Yankton Federal Prison Camp grounds to see Observatory Hill display garden or see other flowerbeds there, you will see the results of Hoffman’s high regard for maintenance of flowerbeds and containers.

“Ongoing maintenance is the key,” Hoffman said. Adequate water and mulching, dead-heading blooms, trimming spent stems, and monitoring for pests all contribute to appearance.

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