Dear Master Gardener: Some of my blue hostas have turned green. They are in a location with afternoon sun. Why have they lost their beautiful blue color?
Answer: Blue hostas need to be in shadier areas in order to retain their blue color. They do best in locations where they receive filtered or dappled sunlight for most of the day. If they do receive sunlight, it is better to have morning sunlight, as it is less intense. Blue hostas are not actually blue. The top layer of a blue hosta leaf is covered with a glaucous coating that gives it a blue appearance. The more glaucous coating a leaf has, the bluer it will appear to be. Hostas are typically bluer when they first emerge, then many turn a blue-green or green tinge later in the growing season. There are some that retain their blue color until autumn. This phenomenon depends on genetic makeup, light levels and degree of summer heat. When blue hostas are exposed to hot sun, harsh watering or certain pesticides, the wax coating kind of melts off and once it’s gone the leaves will not regain their blue color this season. The following blue hostas retain their blue color the best, if planted appropriately: Abiqua Drinking Gourd, Big Daddy, Blue Hawaii, Blue Angel, Blue Umbrellas, Hadspen Blue, Halcyon, Krossa Regal, Love Pat, Powder Blue, Prairie Sky, Silver Bay, and Ultramarine.
Dear Master Gardener: I visited my brother near Mankato and he had yucca plants growing in his yard. I was so surprised to see them growing in Minnesota! I thought they were a desert plant that you might see in Arizona or New Mexico. Is it an annual he’s growing or a perennial that can grow in Minnesota?
Answer: Yucca filamentosa (Adam’s Needle Yucca) is a perennial that can successfully grow in parts of Minnesota. According to the U.S. Department of Agriculture, this plant’s native range is in Wisconsin and Illinois but not Minnesota. This plant is hardy to Zone 4b. Mankato’s hardiness zone is 4b, but most of Crow Wing County is zone 3b. If you have a microclimate in your yard — maybe a protected southside of your house — you could give yucca a try. It is a very showy plant with its sword-like leaves and tall spire of creamy white bell-like flowers. Adam’s Needle Yucca is a long-lived perennial that should be planted in full sun. It reaches a height and spread of 4 feet at maturity, so give it some room. It also has a tenacious root system, therefore, plant it in its permanent home.
Dear Master Gardener: We moved to a new house last spring and there was a big, beautiful perennial garden. Unfortunately, I’ve spent a lot of time trying to eradicate quackgrass and wild onions from the garden. Is there a way to get rid of the weeds without using toxic chemicals?
Answer: Quackgrass, a perennial weed, can invade flower (or vegetable) gardens making it extremely difficult to eradicate. Quackgrass grows from seed or underground rhizomes and reaches a height of about 1 to 4 feet. The stems are smooth with three to six joints. It has thin, flat, bright green leaf blades with a seed spike that appears in July and grows from 3 to 8 inches long. This perennial weed reproduces by seeds and rhizomes. Each quackgrass plant produces about 25 seeds which remain viable in the soil for three to five years. Rhizomes are yellow to white, 1/8 inch in diameter, with distinct joints or nodes every inch or so. Each node is capable of producing fibrous roots, and sending a new blade of grass through the soil. One plant can produce 300 feet of rhizomes each year.
To eradicate them without using chemicals, pull and/or dig the plants as shoots appear, following along the lengths of roots to remove as much as possible. Rhizomes will have to be hand dug as much as possible without breaking them off in the soil because any cutting of the rhizomes means rapid multiplication of plants. Use mulch as much as possible to smother plants, but unfortunately the rhizomes will creep along until there is an area in which it can send up a shoot. If you compost, dry the pulled roots in the sun before composting. You can also eliminate them by constantly slicing the quackgrass blades off with a hoe or trowel. Without photosynthesis the plant will not be able to store food reserves in the rhizomes and will eventually die.
You not only have one annoying weed, but two! Wild onions are a big nuisance because they spread by both underground bulbs and seeds. They are quite resilient, tolerating sunny and shady areas, and can also be difficult to eradicate. Getting rid of wild onions in a flower garden takes perseverance, as it can take several years. Although it isn’t easy, pulling them up is an option. It is much easier to pull them out when the soil is moist. Grab each wild onion plant at its base and pull it upward from the soil. Unfortunately, bulbs or bulblets can remain in the ground and you will see new leaves emerge again later, so try hard to remove all of the plants’ bulbs and roots left in the soil using a thin trowel. Another option is to continuously trim the wild onions to the ground with pruning shears, so the trimmed plants' foliage is unable to photosynthesize. Do not put wild onion in your compost. Either burn it or bury it in a separate spot so nature can break it down without contaminating your compost pile.
Dear Master Gardener: I love hydrangeas! Which ones perform best in our area?
Answer: What’s not to love about hydrangeas?! They have showy summer blooms and many landscape uses. There are several cultivars of Hydrangea arborescens that do well in our climate. Annabelle has white flowers and gets 5 feet by 5 feet. Endless Summer Bella Anna is dark pink and Bounty is white — both mature to 3 feet by 3 feet.
There are at least 16 Hydrangea paniculata cultivars that are hardy here. Some highly recommended ones include: Limelight (white to lime green, 8 feet by 7 feet), Pinky Winky (ivory, 9 feet by 9 feet), Quick Fire (white turning pink, 7 feet by 7 feet), Tardiva (ivory, 9 feet 9 feet), Unique (ivory, 10 feet by 10 feet), Vanilla Strawberry (white to red, 6 feet by 5 feet) and White Diamonds (white to green, 4 feet by 5 feet). If you want a small hydrangea with a lot of flower power, Bobo is smothered with large white flowers that turn pink as the blooms age. It gets 30-36 inches tall and wide at maturity.
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.