Don Gordon's articles - March 2003

Don Gordon is professor emeritus of botany at Minnesota State University. Send questions concerning horticulture or the environment with a stamped self-addressed envelope to him at 52794 Deerwood Trail, North Mankato, MN 56003 or e-mail to osokato@aol.com. Professor Gordon is author of Growing Fruit in the Upper Midwest.

Edible hickory, sassafras, mock orange and tomatoes

(March 26, 2003)

Question: Is there a type of edible hickory that will grow in our area? Hickory nuts are my favorite and I would like to find one for this area that produces abundant fruit.

Answer: There are four species of hickory that are hardy enough for this area, but only two produce edible nuts that are suitable for human consumption. Shellbark hickory, Carya laciniosa, has a thick shell but has sweet edible kernels. Shagbark hickory, Carya ovata, is a Minnesota native species that also produce sweet edible fruit, but the shell enclosing the kernels is quite thin. Due to its bark, I think the shagbark hickory is the most attractive hickory.

Question: I have tried several times to transplant sassafras trees but to no avail. Will these trees grow here in Mankato?

Answer: Common sassafras, Sassafras albidum, is supposedly recommended for our USDA hardiness 4, but very few trees seem to survive in our area. Snyder, in Trees and Shrubs For Northern Gardens, recommends this species for trial in sheltered sites in the eastern parts of zone 4. This species has not survived at the Minnesota Landscape Arboretum. I grew up with this species in Indiana and have had had lots of “sassafras tea.” I do know it is a difficult species to transplant. For best results, the species should be moved ball and burlapped in the early spring.

Question: When I bought my house on Belgrade Avenue in North Mankato I inherited a wealth of interesting plants. One of my favorites is a mock orange, which has the most delightful aroma of anything in the plant world. This mock orange has a highbush cranberry nearby which produces flowers that smell like vomit (literally). I would like to move the mock orange to a location where I can enjoy its bloom without olfactory contamination from the cranberry. When would be the best time to move the mock orange and can it be split?

Answer: Early spring is the best time to transplant sweet mock orange, Philadelphus coroniun. This species has an extensive root system and older specimens are quite easy to divide.

Question: For the last 8-10 years my tomatoes do not get ripe before frost. I mulch with black plastic, old straw or whatever is available. I also rotate the plot each year and use compost for fertilizer. The plants are loaded with tomatoes and I do get enough for the table, but for canning I must ask my friends and neighbors for their excess. I believe I am doing the same thing as I did years ago when I had bumper crops. What am I doing wrong?

Answer: I don’t have a quick fix for the problem, but here are some possibilities.

1. Late maturing varieties: I know the best varieties for canning are often late maturing varieties, but if you are growing varieties that have a maturity date of longer than 80 days, consider growing earlier maturing varieties such as Bush Early Girl VFFNT (54 days), Carnival Hybrid VFFNTAST (68 days) and Jetsetter Hybrid VFFNAST (64 days).

2. Planting time: I am assuming you are planting in mid-to late May. If your planting date is later than this or you are using spindly transplants or direct seeding, this could delay maturity.

3. Excessive pruning will often delay maturity.

4. Has your microclimate changed? Does your garden now get more shade or root competition from nearby shrubs or trees?

Sycamores, plums, vegetable gardens, Asian lilies and spicebush

(March 19, 2003)

Question: Growing up in Iowa we had sycamore trees, which were great for shade, plus they had very aromatic leaves and beautiful bark. I have never seen these trees in Minnesota, but do wonder if they will grow here? Can you provide some information on why these trees are not grown here?

Answer: Sycamore, also called plane tree, is indeed a beautiful tree, but both Platanus x acerifolia (London plane tree) and Platanus occidentalis (buttonwood) are only marginally hardy in our USDA hardiness zone 4. During the last 30 years, local nurseries have occasionally stocked these trees, but the number of surviving specimens has been extremely limited.

The nicest and perhaps the largest specimen locally used to grace a yard along the main highway through St. Peter—until it was destroyed by the tornado that devastated the town a few years ago. In the United States, St. Louis is probably the city with the most sycamores. In Europe, and especially in France, these trees line the boulevards in scores of cities.

William Lass informs me there is a sycamore tree behind the house of James and Paige Attarian at 12 Skyline Drive, Mankato, that is considerably larger than the sycamore that stood in St. Peter for many years. Lass estimates that the tree is about 50 years old and he reports it leafs out very late- usually in late May or early June and is the last tree in the neighborhood to lose its leaves in the fall. Ruth and Will Rankin report they have a “magnificent” sycamore that was planted in 1975 at 806 Garfield Avenue, North Mankato.

Every time someone ask me about sycamores, I am reminded of the story of a botanist who was asked to examine forensic evidence in a rape that was committed under one of these trees. Sycamore leaves have very unusual stellate (star shaped hairs). The presence of these on a suspect’s clothes and in his car helped convict him.

Question: I have two plum trees. One is purple and the other is orange or reddish in color. These trees are approximately 10-12 years old and are self-pollinating. Here is the problem. Both trees bloom early and are loaded with blossoms, but neither tree has ever produced more than a handful of fruit. Do you have any ideas as to what the problem might be?

Answer: I think there are two possibilities. First, some plum varieties that are genetically programmed to bloom early rarely produce abundant fruit because cold temperatures damage the flowers or significantly reduce the number of bee pollinators.

Secondly, there is a good possibility that your plums are not self-compatible and that neither one produces pollen that can fertilize the other. I would suggest that you buy another plum such as ‘Alderman’. This variety developed at the University of Minnesota Horticultural Research Center is super-hardy and has consistently produced abundant fruit every year for well over 20 years. Alderman is self incompatible, but mix pollen from your other trees (and vice versa) should produce an abundance of fruit. If this doesn’t work you will have to try another later blooming pollenizer such as ‘Toka’.

Question: What distance should a vegetable garden be from a farm field? The crop is rotated annually from corn to soybeans. I presently have it 20 feet from the edge of the field.

Answer: I see no problem having the garden right next to the farm field as long as the farmer avoids chemical contamination of your garden. My own garden abuts a farm field, but I have a responsible farmer who is very mindful of the potential damage of pesticide and herbicide drift. Drift problems from a farmer’s field or neighbors' misuse of chemicals should be reported to the Minnesota Department of Agriculture. When planting next to a farm field, use care in selecting sweet corn varieties. Field corn pollen can affect the taste of some genetic types of sweet corn.

Question: I meant to move some Asian lily bulbs last fall but never got around to it. Can they be moved in the spring?

Answer: Asian lilies are usually planted in the fall, but can easily be moved in the spring. For best results move the bulbs as soon as the soil can be worked.

Question: Came across a snippet about spicebush and wondered if it would grow here?

Answer: Spicebush, Lindera benzoin, is recommended for USDA hardiness zone 5. This species might be worth a trial only if you have a very protected spot.

Mulch, okra, Hancock coralberry, blueberries and bluestem grass

(March 12, 2003)

Question: I know you have recommended using black plastic as a mulch for tomatoes, but could you explain why this would be better than clear plastic?

Answer: I think the biggest disadvantage to using clear plastic as mulch for tomatoes has to do with weeds. Most weed seeds need light to germinate. Use clear plastic and you will definitely have more of a weed problem than with black plastic.

Black plastic helps warm the soil, conserves water, prevents weed germination and, most importantly, helps keep the soil born fungal spores that cause blight problems from reaching the lower leaves of the tomato plants. Use black plastic as a mulch on tomatoes labeled V (Verticillium) and F (Fusarium) resistant and you will definitely have fewer blight problems.

In contrast, some commercial growers prefer clear plastic when planting seeds of various vegetable crops. They lay clear plastic in the field a few days prior to planting to warm up the soil. With a warmer soil, germination occurs quicker, and in theory, you have a jump on the competition. Here in Minnesota that strategy is extremely risky and is not something I would recommend.

Question: I am originally from Texas and love okra, but I haven't seen this plant in local gardens. Can you grow this crop in the upper Midwest? If so, can you provide some growing instructions and provide a source for seed?

Answer: Okra is very easy to grow here, just direct seed it in late May when the soil warms up. My only problem with this plant was that no one in the family would eat it. Park Seed (1 Parkton Ave, Greenwood, SC 29647-0001) has a hybrid variety called Annie Oakley II, which they claim performs as well in the North as in the South. Check with local nurseries for availability of this selection and other varieties of okra.

Question: To prevent erosion and for beauty, I am considering planting Hancock coralberry on a gentle slope back of our house. Would this be a good choice?

Answer: Hancock coralberry, Symphoricarpos x chenaultii "Hancock" is an attractive low spreader that is used as a groundcover in USDA hardiness zones 5-7. Unfortunately, it is not hardy enough for our area. Examples of good hardy groundcovers for this area might include creeping juniper, Juniperus horizontalis and cultivars; Japanese garden juniper, Juniperus procumbens and cultivars; Savin juniper, Juniperus sabina and cultivars; Virginia creeper, Parthenocissus quinquefolia; and fragrant sumac, Rhus aromatica "Grow-low".

Question: This spring I want to plant a couple of blueberries that are hardy, ornamental and productive. What would you suggest?

Answer: "Northcountry" is probably the best looking hardy blueberry for our area. Since two different cultivars are necessary for maximum fruit production, I would suggest "Northblue", "Polaris" or "St. Cloud" as a companion. All of these varieties are hardy to minus 30-35 degrees.

Question: In one of my gardening catalogs they gave the scientific name of little bluestem grass as Schizachyrium scoparium. Is this a different plant than the bluestem I know as Andropogon scoparius?

Answer: Schizachyrium is now the correct generic name for little bluestem and Andropogon is considered to be a synonym. There are established rules for naming plants and when the rules aren't followed, names have to be changed. This system of nomenclature is one of the few things in the world that all nations agree upon. Without these rules identifying or buying plants would be a chaotic nightmare. This is why I always try to provide the correct scientific name of plants in this column.

Arborvitae, butterfly milkweed and climate change

(March 5, 2003)

Question: My property borders the new Highway 22 by-pass and three years ago I planted 50 American arborvitae for a windbreak and privacy screen. Nearly half of these trees have had to be replaced and it looks like more will have to be replaced this spring. I was looking through the Henry Fields catalog and noted that they are advertising a Canadian hemlock for privacy screening and property line border. Would the hemlock be a better variety to plant in place of the arborvitae, or would the red cedar you mentioned in a previous column be a better choice?

Answer: Canadian hemlock (Tsuga canadensis) is a Minnesota native, but it performs best in the northern part of the state. In our area this species must be grown in a protected spot to avoid severe winter windburn damage. I would guess there is only a handful of surviving hemlock in Blue Earth County. I know one individual who planted 500 of these and not a single one survived. Hemlock nursery stock from out of State sources almost always fails in open areas. In our yard, we are fortunate to have a beautiful specimen that is over 25 feet tall.

Thuja occidentalis (Techny arborvitae) might be a good replacement. It is the best arborvitae available and it makes a good hedge plant. Eastern red cedar (Juniperus virginiana) is an excellent super-hardy plant that it very useful for screens and hedges. This is the species I prefer. Both Techny arborvitae and red cedar are available from local nurseries.

Question: Can you tell me when and how to transplant butterfly milkweed?

Answer: Established plants of Butterfly milkweed (Asclepias tuberosa) are extremely difficult to transplant, and it is not something I would recommend. These plants are easy to grow from seed and several nurseries offer young seedlings for transplanting.

Each year we lose hundreds of butterfly milkweeds from roadsides and native prairies to gardeners who attempt and usually fail to transplant them to home gardens.

Those big increases in crop production that we have seen during the last two decades have usually been attributed to improved varieties, plus generous use of fertilizers, herbicides and pesticides. Now a new report in a recent edition of Science challenges that assumption. Researchers at Stanford University found that a "surprisingly high percentage of the improvement in yield was not due to farm management but to climate change." This research suggests that food production in the United States may be more vulnerable to shifts in climate than was previously thought, and, of course, this also has implications for global food security.

From 1982 to 1998 corn and soybean production increased by 30% over a large swath in the Midwest. The researchers found about 20% of this increase was due to climate (primarily cooler summers) and the remaining 10% increase was attributed to management and increased levels of carbon dioxide.

Now here is the shocker. Almost all climatologists are predicting that global warming will produce a warming of the Midwest Corn Belt. This research suggests that yields will drop by 17% for each degree that the growing season warms. Many researchers warn that a drop in U.S. production could stimulate planting of more soybeans in environmentally sensitive areas such as Amazonian watersheds in Brazil.

The Environmental Protection Agency (EPA) has given Monsanto permission to market genetically modified (GM) corn that is resistant to corn rootworm. This pest causes over $1 billion in damages each year to the U.S. corn crop.

Last week the Wall Street Journal reported that some companies that buy corn are urging farmers to shun this type of GM corn because it has not been approved by the European market, an important export source for the U.S. corn crop.

All articles © Don Gordon 2003. For information about reprints, copies, or use of the material, contact Don Gordon, 52794 Deerwood Trail, North Mankato, MN 56003 or e-mail to osokato@aol.com.