Ask the Master Gardener: Longer-blooming perennials keep the colors flowing through the growing season

Now is the time to start thinking about taking care of plants for the fall.

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Agastache 'Blue Fortune.' Photo by Jennifer Knutson

Dear Master Gardener: What are some of the longest blooming perennials for our area?

Answer: Many perennials have a short blooming period, so it is beneficial to add perennials that have a long blooming period or rebloom to keep continuous color going throughout the growing season. Blue Fortune Agastache has been blooming in my garden for the past six weeks and still looks fabulous. It gets 2-3 feet tall and has lots of lavender-blue, bottle brush-like flowers with licorice scented foliage. It requires full sun and tolerates heat and drought once it’s established. It is a pollinator magnet -- my plants are usually covered with bees, butterflies, and hummingbirds. Another pollinator friendly perennial that blooms for months in my garden is Echinacea (cone flowers). White Swan and Magnus perform the best in zone 3. I am not deadheading my Echinacea now because the birds love the seeds. There are many new cultivars of Nepeta (catmint) that range in size from the dwarf cultivar Kit Kat to the large Walker’s Low. Not only do they have a long blooming period, but if you give them a good haircut after the initial flush of flowers by shearing them back to about one-half, you will encourage a tidier mound of foliage and get another flush of blooms that will continue until frost. Achillea (yarrow) blooms early to mid-summer for 6-8 weeks and is a butterfly favorite. You may want to keep it deadheaded as it can be an aggressive spreader. Although I hesitate to declare that a plant is “deer-resistant”, these are all known to be plants that the deer usually avoid and in my experience the deer bypass them for tastier treats like hostas and roses.

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Agastache 'Blue Fortune.' Photo by Jennifer Knutson

Dear Master Gardener: Should I cut back my Clematis this fall, and if so, how close to ground level?


Answer: It depends on what type of Clematis you have. There are three different groups of Clematis based on their pruning needs. The plant tag will usually tell you which group your plant is in. Group 1 Clematis flowers grow on old wood -- this is the least preferred for cold climates and typically not sold or grown here. Group 2 flowers on old and new wood -- many of these are zone 4 plants, but some do well here in zone 3. Typically, little pruning should be done for woody-stemmed members of this group. If cut to the ground or pruned in fall or spring, flowering will be reduced or delayed, but not prevented. Group 3 are the late-blooming cultivars that produce flowers on new wood. Jackmanii, one of the most common and popular in Group 3, is an example of this group. These are the hardiest for us in zone 3. They can be cut to within a few inches of the ground in late fall or spring. I cut my Group 3 Clematis down in early spring to about 12 inches above the soil line. I usually don’t prune my Group 2 Clematis. However, if a vine shows signs of Clematis Wilt during the growing season, I then prune the affected stem to the ground at that time to try to eradicate the disease. If you have very old, declining vines, you may need to remove the stems completely to the ground to rejuvenate the plant. If you just planted your Clematis this year, it should be hard pruned to stimulate growth during the first spring after planting, regardless of whether it is in Group 2 or 3. Hard pruning (close to ground level) will promote an increase in blooms. Light pruning is the safest for all types of Clematis, so if you don’t know which group your Clematis is in, play it safe and lightly prune it or don’t prune it at all.

Related: Master Gardener: Be on the lookout for invasive jumping worms
Dear Master Gardener: When should I dig up my calla lily, canna, dahlia, and gladiola bulbs to store for the winter?

Answer: Summer blooming bulbs, such as calla lilies, cannas, dahlias, and gladioli, can be dug up in the fall, stored over winter, then planted again in the spring to enjoy another year. These tender bulbs cannot survive our cold winter temperatures and need to be stored in a cool, dry place over the winter. Wait until the first frost has damaged the leaves. Dig up the bulbs with a spading fork and cut the stems back to about two to three inches. Let them dry in a cool place out of direct sunlight for a few days before storing them (gladiola corms should be cured longer -- two to three weeks). When they are dry, brush off excess soil that clings to them. Dahlias should be washed off with a gentle stream of water before they dry for several days. Clean tubers have fewer disease opportunities. A light dusting of powdered sulfur helps too. Check your bulbs for any signs of disease and keep only those that are healthy. Place the dried (cured) bulbs in peat moss, vermiculite, sawdust, or shredded paper in paper bags or ventilated cardboard boxes in a cool part of the house (basement or heated garage) where they will not freeze. Optimal storage temperature is 45-50 degrees. Check on them occasionally to see how they are doing – throw away any bulbs that get soft and mushy or have signs of mold.

Related: Ask the Master Gardener: Keeping a garden colorful through autumn
Dear Master Gardener: I have a small yard and would like to plant some dwarf evergreens. Which ones do you recommend?

Answer: Dwarf evergreens are a great addition to the landscape! While they can be planted in the fall, the best time to plant them is spring. Dwarf evergreens can be prone to root problems, so it is very important to make sure the plant is not root bound when planting it. Prune the roots and tease them out so they will migrate outward and won’t girdle. It is very important to keep conifers well-watered until the ground freezes to help them survive our extreme cold. Here are some dwarf conifers that perform well in zone 3:

  • Hetz Midget arborvitae is green, gets 2-3 feet tall and wide, and stays in a perfect globe. It grows well in full sun to light shade.

  • Golden Globe arborvitae gets 2-4 feet tall and wide. It has yellow foliage.

  • Tiny Tim arborvitae has green foliage. It grows to only one foot tall and wide.

  • Piccolo dwarf balsam fir will reach 3 feet tall and 4 feet wide at maturity. It prefers sandy, acidic soil (common in the Brainerd lakes area). It grows well in full sun to light shade.

  • Dwarf globe blue spruce has bright blue foliage, is globe-shaped, and reaches 5 feet tall and 6 feet wide at maturity.

  • Bird’s Nest spruce is green and has a nest-like appearance. It reaches 3-5 feet tall and 4-6 feet wide at maturity.

  • Glauca Nana dwarf scotch pine has blue-green needles and grows slowly, eventually reaching 6 feet tall and wide.

  • Slowmound mugo pine grows to 2-3 feet tall and wide at maturity. It has dense, deep green needles and an even mounding habit.

  • Dwarf blue Rocky Mountain fir has striking blue needles. It grows into a dense, pyramidal shape and takes about ten years to reach four feet in height. It will eventually become 8 feet tall and 6 feet wide.

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 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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Agastache 'Blue Fortune.' Photo by Jennifer Knutson

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Agastache 'Blue Fortune.' Photo by Jennifer Knutson

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