Dear Master Gardner: My cousin in southern Minnesota has an old shagbark hickory tree and the bark is so beautiful! Is this a native tree and will it grow in north central Minnesota?
Answer: Shagbark hickory (Carya ovata) is native to the southeast corner of Minnesota — the northern edge of its range. It is hardy in zones 4-8. Shagbark hickory reaches a mature height of 70-90 feet. The bark on mature trees is unusual and very beautiful as it exfoliates in long strips
giving it a “shaggy” appearance. Equally ornamental are the scarlet scales of emerging leaf buds, which unfurl like petals of a flower surrounding the emerging compound leaves. Shagbark
hickory blooms in May. The male flowers are pendulous catkins and the female flowers are short spikes that develop into edible, oval nuts. The nuts are delicious and nutritious! Autumn color is yellow to golden brown.
Dear Master Gardener: Last year in late spring/early summer there were caterpillars on my Colorado blue spruce tree that caused extensive defoliation. What should I do this year to protect the tree?
Answer: Let me first start out by saying that the Colorado blue spruce (Picea pungens) is not native to Minnesota and no longer recommended by the U of M due to its susceptibility to several debilitating spruce diseases, most specifically Rhizosphaera needle cast and Cytospora canker. They are much more prone to infection than our native white or Norway spruce.
Regarding the caterpillar problem, the most likely culprit is either the spruce budworm or the yellow-headed spruce sawfly. The larvae of the spruce budworm are olive brown or reddish-brown caterpillars, that get approximately 1-1 ½ inch in length at maturity. They become active in mid- to late-May and can extensively defoliate trees. The yellow-headed spruce sawfly tends to attack isolated spruce, like those found in landscapes. The larvae have yellow or reddish-brown heads and olive-green bodies with six gray-green stripes, and are three-fourths inch in length.
They appear and begin feeding in late May to mid-June and feed for about 4-6 weeks. Three to four consecutive years of defoliations can kill a tree. To try to eradicate the damage-causing insects, spray foliage when larvae are less than or equal to half their full-grown size and before damage is extensive. Bacillus thuringiensis (Bt) can be used for the spruce budworms but is not effective on sawflies. Insecticides that are effective for either one are: acephate, azadirachtin, bifenthrin, fluvalinate, insecticidal soap, malathion, permethrin, pyrethrins, and spinosad. It is essential to read the label before you buy a pesticide to be sure it is registered for the pest you wish to treat. Read the entire label and observe all safety precautions on the label.
Dear Master Gardener: This week I saw some brilliant, dark pink, low-growing flowers growing on top of and spilling over a boulder wall. They are gorgeous — what are they?
Answer: It sounds like Phlox subulata, also known as creeping phlox or moss phlox, which is in bloom right now and looking quite spectacular! Phlox subulata is native to parts of Minnesota. It is a great addition to rock gardens and will drape slightly over a rock or retaining wall. It makes an excellent ground cover for sunny areas. Moss phlox has a creeping habit that creates a carpet of flowers that blooms in late May and early June. The plant grows to about 6 inches tall and spreads to about 24 inches wide by stems that root where they touch the ground. It grows best in full sun but will tolerate part sun. Cultivars come in pink, white, lavender, and magenta. Moss phlox is a plant that attracts butterflies and other pollinators and is not typically preferred by deer.
Baptisia australis, also known as blue false indigo, is an underused perennial that makes a fabulous addition to the sunny garden. It is a long-lived perennial that has a shrub-like appearance.
Contributed / Jennifer Knutson
Dear Master Gardener: A friend said he is putting in a baptisia. What type of plant is that?
Answer: Baptisia australis, also known as blue false indigo, is an underused perennial that makes a fabulous addition to the sunny garden. It is a long-lived perennial that has a shrub-like appearance and reaches 3 to 4 feet in height and width at maturity. Choose its final resting place because it has a long tap root and does not transplant well. The soft bluish-green foliage looks lovely all season long. It is in the pea family and has long, lupine-like spires of pealike flowers that bloom in June. The flowers last about two to three weeks. Various shades of blue and purple are the most common colors, but you will also find new cultivars that come in yellow, white, and cream. Cherries Jubilee is a maroon and yellow cultivar for those University of Minnesota fans! After those beautiful flowers have faded away, they are replaced by interesting green, oblong seed pods that grow 2 to 3 inches long, then turn charcoal black in late summer or early fall. They have considerable ornamental interest! The mature seedpods contain seeds which rattle around when shaken. In fact, children once used them as rattles. Baptisia australis is deer and rabbit resistant, hardy to zone 3, attracts butterflies, has multi-season interest — your friend is adding a great plant to his garden!
Dear Master Gardener: I purchased what I thought was a Mandevilla to go up my obelisk in a container but it isn’t vining. A friend purchased a Dipladenia and it looks like mine. Are they the same plant with different names? Why isn’t my plant vining?
Answer: Mandevilla and Dipladenia are in the same family and look similar, but they have different growth habits. Mandevilla is a vine and Dipladenia is more shrub-like. The flowers and leaves of Dipladenia are smaller than Mandevilla, more pointed, and slightly glossy. Mandevilla is a vine and needs a structure for climbing. Shrub-like Dipladenia is great as a filler plant in a container. When you go to the garden center, be careful that you are choosing the right plant as one can be labeled as the other. Since the plant you purchased to climb up your obelisk isn’t vining and is staying shrub-like, you probably got a Dipladenia rather than the intended Mandevilla.
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.