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Ask the Master Gardener: Meet bottle gentian, one of Minnesota's unusual and beautiful native flowers

Bottle gentians are a long-lived perennial that bloom in August to September and are a lovely addition for late season color.

A photo of a bottle gentian flower
Bottle gentian have royal blue, bottle-like flowers that never actually open and look like large buds. The blooms are pollinated exclusively by bumblebees.
Contributed / Shutterstock
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Dear Master Gardener: A friend ordered a flower I’ve never heard of called bottle gentian. What can you tell me about it?

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Answer: Bottle gentian (Gentiana andrewsii) is a Minnesota wildflower that is found in most of the state. The plants have gorgeous royal blue, bottle-like flowers that never actually open and look like large buds. The unusual blooms are pollinated exclusively by bumblebees, which are large and strong enough to open the flower and crawl inside. Bottle gentians are a long-lived perennial. Plant them in full to part sun (they will be sturdiest in full sun) in rich, moist soil. They bloom in August to September and are a lovely addition for late season color. It may not be easy to find, so you may have to order bottle gentian from a nursery that specializes in native plants.

Dear Master Gardener: My vegetable garden hasn’t been very productive this year. I have healthy looking cucumber plants with no cucumbers and bean plants with no flowers. Is the unusually hot summer causing it?

Answer: People around the state are reporting disappointing yields in their vegetable gardens and many of the problems are related to persistent high temperatures. According to the U of M, some of the issues that can be causing problems are: too much fertilization, hot daytime and nighttime temperatures cause flowers to drop, hot temperatures change what type of flowers some vegetables produce and some bees don’t like it hot. It’s tempting to baby our plants by feeding them more, but too much nitrogen results in nice green foliage with no harvestable vegetables, especially with vining vegetables (cucumbers). When both the nighttime and daytime temperatures are high it can cause flowers on plants to abort (form then die and fall off without pollinating). Flower abortion occurs at temperatures of 75-95 degrees. The U of M reports that dropped flowers have been noticeable in tomatoes this year. Green beans can also abort flowers in hot temperatures (over 95 degrees), especially if the soil is dry. In addition, during periods of hot weather, bean flowers produce less pollen, which results in fewer, smaller beans. Hot weather also causes bees to slow down and pollinate less. This is especially true in crops like cucumbers, which have small flowers that aren’t really attractive to many bees.

Dear Master Gardener: I saw an insect on one of my flowers that looks like a hummingbird. What type of insect is this and can it damage my flowers?

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Answer: The insect you most likely saw, and that frequently gets mistaken for a hummingbird, is a moth. The hummingbird moth, or hummingbird clearwing, has a wingspan of 1½-2¼ inches, and lacks scales on most of its wings, with the exception of a dark border around the edge of its wings. Another moth that hovers around flowers like a hummingbird is the white-lined sphinx moth. This moth is larger than the hummingbird moth, has a wingspan between 2-3½ inches, and has scales covering its wings. Its first pair of wings are dark colored with a white stripe running from the wingtip diagonally to the base of the wing, and the second pair of wings is dark with a pink-red band. Like hummingbirds, both moths hover and flit about in flower gardens. Whereas a hummingbird has a long beak, these moths have a long proboscis that they use to feed on nectar while they are flying. They prefer feeding on deep-lobed flowers. Moths are the preferred food of birds, so most moths fly at night to avoid being consumed; however, these hummingbird-like moths fly during the day. You are most likely to see these moths feeding around dusk and they are active July through September. They do little, if any damage to garden plants.

Dear Master Gardener: We have an annual family get-together in August. What blooms in August so my gardens have some color for our big event?

Answer: There are many beautiful plants that bloom in August — and they’re often on sale at this time! Perovskia (Russian sage) blooms July through September and produces lavender flowers on scented, silver-gray foliage. It’s hardy to zone 4, but many gardeners grow it successfully in zone 3. The flowers of Helenium (Helen’s flower or sneezeweed) range from yellow to maroon, with many being a blend of yellow and russet tones. Coneflowers, sunflowers, and goldenrods will add yellow tones. There are many late-blooming daylily cultivars of various colors from which to choose. Lobelia cardinalis (cardinal flower) produces bright scarlet-red flowers and attracts hummingbirds. Aster, boltonia, Joe Pye weed, balloon flowers, liatris, gaura, hardy hibiscus, and tall sedum also bloom in August. Mums are starting to bloom already (the tags tell when their bloom starts). A shade plant that blooms at this time is Actaea, also known as Cimicifuga, which has very fragrant, bottle brush-like flowers. Many hydrangeas bloom this month. Annuals give the most color — dahlias should be in their prime starting in August. You should be able to put on quite a show of color for your family get-together!

Dear Master Gardener: I have recently planted some shrubs and would like to mulch them with some of my many white pine needles. My wife, however, says that pine needles will make the soil acidic and I shouldn’t use them. Is she right? If so, what should I use?

Answer: It’s a longstanding myth that pine needles acidify soil. University tests show that there is little, if any, acidifying of soil from pine needles. Pines thrive in acidic soil but do not significantly acidify it themselves. Go ahead and mulch with them. Pine needles are plentiful in this area. Other mulch options are wood chips, bark chips, shredded wood chips, cocoa bean hulls (which emit a mild and delicious chocolate aroma), wild rice hulls, and many others. Mulch has many benefits. It conserves moisture in the root zone of plants, prevents weed growth, stabilizes soil temperatures, prevents the spread of soil-borne diseases, increases the fertility of soil as it decomposes, and gives a tidy appearance. In the winter mulch does not prevent the soil from freezing but it minimizes the heaving up of plant crowns from alternate freezing and thawing. Rock and stone mulches are attractive but are not weed-free, as many assume. They tend to compact soil, and are extremely difficult to remove.

You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at umnmastergardener@gmail.com and I will answer you in the column if space allows.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.

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