150 Years of Hardy Plants


Cover of 150 Years of Hardy Plants.

Originally published in 2000 for the University's 150th year, 150 Years of Hardy Plants is an illustrated catalog of all U of M releases of horticultural plants from apples and grapes to azaleas and chrysanthemums, and the research that went into their development up until 2000. 

A printable PDF version can be found in the Digital Conservancy. Content from the publication is also available digitally below.

Today, CFANS horticultural scientists and breeders are focused on breeding new varieties of plants and developing new techniques that will help expand the growing season in Minnesota or, in some cases, allow Minnesotans to grow plant varieties they were not able to grow in the past. Visit the MAES news feed for updated information on U of M fruit, vegetable, and landscape plant development research and variety releases.

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Tree Fruits

The Unversity's fruit breeding program began nearly a century ago and is one of the oldest continuous programs in North America.

With support from the Minnesota State Horticultural Society, plant breeders faced the challenge of the rigorous Minnesota climate, from extreme subzero winters to hot and dry summers. In the early 1900s, parent trees were collected from the wild as well as from Midwest and New England growers. Early researchers produced thousands of fruit seedlings from those parent trees. As with research then and now, hard work combined with chance led to major breakthroughs. The winter of 1917-18 set records for extreme cold; however, some progeny of "Malinda" - a New England apple - survived and were a boon to Minnesota's breeding program. "Haralson," "Folwell" and "Minnehaha" were siblings released in the early 1920s, and some of "Malinda's" genes live on in "Honeygold" and even "Honeycrisp"™. The plethora of U of M plums introduced in the 1920s can also be traced to the severe test winter of 1917-18.

Today, U of M researchers combine traditional plant breeding methods with modern techniques. Laboratory freezing tests during the winter help select the hardiest grape selections without waiting for the once-in-a-decade test winter. Precocious dwarfing rootstocks reduce the years and space required to grow thousands of seedlings. In vitro or "test tube" micro-propagation (tissue culture) provides a rapid means of propagating disease-free stocks of blueberries, raspberries, and grapes. And recently, U of M scientists made plant acquisition expeditions to capitalize on the hardiness of wild varieties in the extreme climates of Kazakstan and China. At the end of the century, only a few states have fruit breeding programs and the U of M is the last major program in the Midwest.


Growing apples is fun and rewarding, but failure to bear fruit is a common problem. Several factors may account for this including inappropriate site, improper cultural care, insufficient sunlight, stress from insects or disease, or poor pollination.

A plant only blooms when it reaches maturity. Most standard fruit trees require five to seven years after planting before they will bear fruit; dwarf trees usually bear within three years.

Fruit trees require at least eight hours of direct sun daily to grow, flower, and fruit well. Annual pruning and pest management is also required to maintain optimum health. But even with good cultural practices, a particularly harsh winter or a hard freeze in early spring can ruin that year's flower buds. Fruit trees that bloom very early, such as apricots, tart cherries and plums are especially vulnerable.

Even rainy weather during bloom can reduce or eliminate a crop by hindering the insects necessary to pollinate the flowers. Apples, apricots and hybrid plums require that two different varieties be located within 100 feet for pollination to occur.

Small Fruits

Much of the University of Minnesota's small fruit research takes place at the North Central Research and Outreach Center at Grand Rapids, where horticulture, agriculture, and forestry research has been underway since 1896. Here, fruits, vegetables, trees, shrubs, and flowers receive their maximum test for winter hardiness at the coldest horticultural research center in the continental U.S.

Blueberries, currants, and strawberries are grown as ornamental plants, as well as for fruit. Strawberries, currants, gooseberries, and raspberries are easy to grow in most of Minnesota. Blueberries require acidic soil, with a pH of 4.0-5.0. Have your soil tested through your county Extension office.

Strawberries can be grown as a ground cover and usually benefit from winter protection. June-bearing strawberries produce a large, concentrated crop in late spring. Everbearing types produce two smaller crops, one in late spring and one in early fall. The newer day-neutral plants are capable of producing fruit throughout most of the growing season. Strawberries normally yield 5 to 10 pounds of fruit per 10' of row.

Currant and gooseberry plants are easy to grow and do best in soils with a pH of 5.5-7.0. Hardy and productive, they provide fruit for jams and desserts. A mature gooseberry or currant can produce up to four quarts of fruit annually.

Ornamental Trees

Proper planting is critical if you want healthy, vigorous trees and shrubs. Start with a hole at least twice as wide as the rootball. If you're planting a tree or shrub with a main trunk, gently brush soil away from the stem to find the first root closest to the soil surface. This area is the 'root flare,' the transition zone between a tree's trunk and roots.

When a tree or shrub is planted too deeply, the roots may partially or completely encircle the trunk above the root flare and interrupt the flow of sap to the roots. Eventually, the flow stops and the tree dies. This condition — known as girdling root syndrome — may also cause the tree to fall in a windstorm, as U of M researchers documented in the severe storms of 1998.

Adjust the soil depth in the planting hole so the first root will be just below the soil surface. When you fill the hole you may add compost, peat or composted woodchips to replace up to one-third of the original soil volume. For proper drainage, it is vital that the soil you use for backfill consists mostly of original soil.

Water regularly during the first few growing seasons until the plant is well established. The type of soil (clay, sand, etc.) will determine how much water is needed.


When to prune small trees and shrubs depends on when they flower. Plants grown primarily for early spring flowers (on the previous year's growth) should be pruned immediately after they finish blooming. This includes azaleas, forsythias, pearl bush, flowering plums, crabapples, and redbuds. Fruit trees are best pruned in late winter before they begin new growth.

Shrubs grown primarily for their foliage, rather than showy flowers, should be pruned in spring before growth begins. This includes dogwood, honeysuckle, barberry, alpine currant, purpleleaf sand cherry, smokebush, and buffaloberry.

Shrubs that bloom on new growth may be pruned in spring before growth begins. Plants with marginally hardy stems such as clematis and shrub roses should be pruned back to live wood. Hardier shrubs such as late-blooming spireas and smooth (snowball) hydrangeas should be pruned to the first pair of buds above the ground.

Prune older or overgrown shrubs every year by removing up to one-third of the oldest, thickest stems or trunks, taking them down to the ground. This will encourage the growth of new stems from the roots. Once there are no longer any thick, overgrown trunks left, switch to standard pruning as needed.


In the 1930s the chrysanthemum breeding project at the U of M was initiated. Since then, 76 garden mums and seven greenhouse or florist mums have been introduced.

Today, Minnesota maintains the only public mum breeding project in the country. U of M scientists make hybrids in the winter and plant out hundreds of seedlings the following spring to compare them to the best performers. Trials are conducted in St. Paul and at six other U of M Research and Outreach Centers, which represent the variability of Minnesota soil, moisture, and climate. Plants are evaluated for flower size, color, growth habit, vigor, frost tolerance, and winter hardiness.

Showy perennials that flower from August until frost, these U of M mums are uniquely developed to withstand USDA Zone 3 and 4 growing conditions and will usually overwinter when covered with a protective mulch in late fall. Mums prefer full sun and well-drained soil. For best flowering, have your soil tested (contact your county Extension office to obtain directions) and add fertilizer if necessary. Pinching has long been recommended on mums but is not required. Pinching the branch tips anytime from early June until July 4 will delay flowering and produce shorter, more compact plants. Left unpinched, plants will flower earlier and have taller, more irregular growth. The University does not pinch any of their field trials. Over time, mums increase in size and can become crowded. When that happens, dig and divide the plants in early spring just as growth starts.


Nearly 80 years ago, 'Kitchenette' — an early maturing winter squash — was the first vegetable introduced from the vegetable breeding program of the U of M Agricultural Experiment Station.

Since then, numerous vegetables have been introduced, with improved disease resistance and early maturity suitable for growing in our North Central region. These new gene sources use less garden and agricultural chemicals. 'Mincu' cucumber, 'Minnesota Midget' muskmelon, 'Greengold' and 'Rainbow' winter squash, are heirloom or historical varieties that are still sold by specialty growers.


Sunlight and high temperatures are needed to completely ripen grapes, so plant vines on a south-facing slope, or on the south side of a building or windbreak.

They are best adapted to the southern half or two-thirds of Minnesota. Avoid sites with standing water and poor drainage, and add fertilizer based on soil test recommendations. Grapes require annual pruning. Hardy varieties are often pruned to four main canes with 40-60 buds per vine for table varieties, and 20-30 buds for wine varieties. Tender varieties requiring winter protection are pruned to a single trunk that can be removed from the trellis and protected on the ground over the winter.


Tips for azaleas:

  • do best in full sun, will tolerate light shade
  • are sensitive to extreme heat (avoid the south side of buildings)
  • have shallow root systems that dry out rapidly
  • benefit from watering, so good drainage is a must
  • require acid soil for best growth
  • benefit from compost, manure, sawdust, or peat moss before planting
  • should not be planted too deep; roots form in the upper 4 to 6"
  • need fertilizer in spring or early summer
  • need an organic mulch to retain water during dry periods