Don Gordon's articles - April 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.

Oak construction damage

(April 30, 2003)

Question: My husband and I are building a new home in a wooded area west of St. Peter. Naturally, we are concerned about saving as many trees as possible. There are 5 very large oak trees near the back of where the house will be located. We are wondering how close we can place the house to these trees and still insure their well being? The trees are anywhere from 26-30 inches in diameter.

Answer: Oaks have a deep tap root and can withstand some lateral root damage. Here is a personal example. Our home built in 1972 has a large bur oak on the north side located 8 feet away from the foundation and another on the south side located 13 feet from the house. The trees survived construction, but after a few years, they seemed to lack vigor. I then had both trees pruned to remove dead wood and to compensate for the root loss. That pruning was like a magic elixir and today these 100 year old trees appear to be very healthy.

Building in a wooded area and deciding which trees to save is always a challenge. I would be hesitant to leave trees that lean towards the house or those that have major branches extending over the roof line. Cutting some small trees may also reduce competition and improve the growth of others. Above ground parts of oaks damaged during construction may be more vulnerable to oak wilt. To minimize this damage, fence off the trees you are trying to save and restrict all pruning to the fall or dormant season when oak wilt is not a threat.

Another concern in saving trees during construction is grade change. A friend paid $50,000 for a lot with several big bur oaks. A few years after construction nearly all the trees were dead because of grade change. I call this “bulldozer wilt.” Don’t expect trees to survive if tons of soil have been piled on their roots.

Question: Can you recommend a shrub for the southeast corner of a deck which is 15 feet from a black walnut tree? I tried a "Nearly Wild" rose, but it didn't survive.

Answer: Many plants are damaged or killed by the toxic chemical juglone that is produced by walnuts and butternuts. Examples of shrubs that are tolerant to juglone would include: Daphne mezereum, February Daphne; Euonymus hamiltoniana, Hamilton euonymus; Juniperus chinensis Pfitzer, Pfitzer chinese juniper; Lonicera tatarica, tartian honeysuckle. A more extensive list of juglone tolerant plant has been prepared by University of Wisconsin IPM Specialist, Karen Delahaut . Her list which includes shrubs, trees, herbaceous annuals, herbaceous perennials, vegetable and fruits is available on the web at http://www.uwex.edu/ces/wihort/landscape/Juglone.htm#Trees&Shrubs.

Question: We have a row of evergreen shrubs along our driveway that came out of the winter all brown. My husband thinks the neighbors put salt on them. What could cause this?

Answer: I can’t speak for your neighbors, but this browning of evergreens is a common complaint I have been receiving. Some varieties of arborvitae, Thuja, and junipers, Juniperus, seem to have been damaged extensively. The damage this year is very similar to what happened about 20 years ago. I think this browning is caused by unusually warm winter temperatures followed by a sudden drop in temperature. For now, I am advising doing nothing. In a couple of weeks, prune out the obvious dead parts and then see if there is enough green left to warrant saving.

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This is the week to apply corn gluten meal (CGM) if you want to inhibit germination of crabgrass, dandelion and nearly 20 other common lawn weeds. Use 20 pounds per 1000 square feet. There is a wide variation in price and if dollars are a concern, I would recommend comparative shopping. Water is necessary to activate CGM. If there is no rain for a week after application, be prepared to help nature. CGM contains 10% nitrogen; thus in most cases, there is little need to apply additional fertilizer.

Earth Day 2003

(April 23, 2003)

Yesterday was the official date for Earth Day, an annual event I have been writing about since the inception of this column in 1976. After rereading all those columns, I was struck by how similar they all were. Nearly every one made a plea for preserving the biosphere for future generations and for shifting the emphasis from a symbolic one-day celebration to an event that dominates our lives everyday. Lets look at some highlights of those columns during the past few years.

In 1995, the entire Earth Day column was devoted to hubris. Hubris is overwhelming pride that precedes a fall. Hubris is the belief that our way of doing things is far superior to anything done in the past. Hubris is the mistaken belief that the only species on Earth that really matters is Homo sapiens. Hubris is also the mistaken belief that economic growth alone is the panacea for this nation’s or the world’s problems.

In 1996, 28 major pieces of environmental legislation were profiled and those politicians in Washington who used hubris to try and convince us that major environmental problems had all been solved were taken to task. They argued forcibly that existing environmental laws were an impediment to increased economic growth. The architects of the Contract with America used hubris along with insolence and arrogance to argue that the Endangered Species Act was stifling economic growth.

In 1997, Global warming was a major feature of the Earth Day column. Quotes from Mostafa Tolba, Executive Director of the United Nation’ Environment section (“no nation can cordon itself off from its neighbor’s pollution”) and environmentalist, Norman Meyers (“the winds carry no passports”)reminded readers that curbing global warming will require international cooperation on an unprecedented scale.

In 1998, further evidence of environmental degradation was presented. Over 50% of the remaining primates (our closest relatives) are threatened with extinction. Coral reefs around the world are dying. Global fisheries are collapsing. Forests are shrinking. One quarter of all bird species have been driven to extinction. Water tables are falling on every continent. Topsoil losses worldwide cost $400 billion a year.

The Earth Day 1999 column took a look at the tremendous gains in food output, but concluded that our agricultural system is clearly out of whack. The people who grow the food have become pawns of a few select multinational corporations who control prices of inputs and outputs of agriculture. Housing huge numbers of animals in small confined spaces creates disease problems. It doesn't take a rocket scientist to figure out that overuse of antibiotics will create resistant bugs. In addition, waste from these factory farms is 130 times the volume created by humans and it is creating a public health risk in 29 states.

In 2000, the story of how subsidies that promote fossil fuels 10-15 times more than clean and renewable sources of energy promote environmental ignorance was presented. The true price of gasoline including military expenditures was calculated at $6 per gallon. Other subsidies that globally total $1.5 trillion promote intensive agriculture, forest destruction, wasteful use of water and destruction of marine fisheries.

In 2001, more evidence of global warming was presented. The editor of Science took the President to task for his inaction. The Administration was also criticized for their plans to open up the Arctic National Wildlife Refuge for oil and natural gas exploration. He was also criticized for attempts to lower drinking water standards and for indefinitely tabling a number of environmental rules passed during the Clinton Administration.

In 2002, the 1.2 billion people who make less than $1 per day were profiled. This poverty according to plant geneticist, Charles Arntzen, “is the single biggest threat to world peace.” Poverty is also the single biggest threat to the environment. Don’t expect a person who makes less than a $1 a day to care much about saving species, air or water pollution.

In 2003, some critics and many nations would argue that the United States suffers from hubris. The President’s attention or inattention to the environment gets rather low marks from mainstream environmentalists. Global warming has been largely ignored and continued reliance on fossil fuels at the expense of alternatives seems to be the course we are on.

Globally, world population, despite some slow down, may double to 12 billion in 50 years. How to feed these people will be a challenge because global food production has been declining for two decades. David Pimentel reports that growing water shortages are plaguing agricultural production. Agriculture consumes 70% of the world’s fresh water. He reports that “in some areas water is so polluted that it is unsafe for agricultural production and 90% of human infections with diseases in developing countries are attributed to polluted water.”

Safe compost?

(April 16, 2003)

Question: I plan on buying some compost for my mothers vegetable garden this spring from the SMC site off Third Avenue. Someone in my office brought up the subject that with all the arsenic treated wood that can be chipped up for compost and other chemicals that can be sprayed on vegetation prior to composting-this may not be something I want to put in a vegetable garden. Is this compost safe?

Answer: Each year I buy several yards of compost from the SMC site. I use this compost strictly for flowers, shrubs and trees. It may be perfectly safe, but it is not something I would recommend for the vegetable garden. I am not so worried about arsenic because the facility will not accept treated lumber containing this chemical. I am concerned about other potential problems with certain pesticides that take a long time to break down. There is no way of knowing what chemicals might be present in this type of compost.

I should point out that my views are not shared by all. A few years ago an official from the National Composting Council sent me a letter extolling the virtues of this compost for the vegetable garden. Compost is great for the garden, but only if you make your own or know exactly how it was treated.

Question: I have a Sweet Sixteen apple that has many blossoms each spring, but it always produces less than five apples. I have a Fireside apple next to it that produces very well. The Sweet Sixteen produces much later than the Fireside. Could it be that I need another tree that blooms at at the same time to get good pollination?

Answer: Yes, I think this may be the answer to your problem. Both Sweet Sixteen and Fireside are considered to be mid-season bloomers, but the Sweet Sixteen pollen may not be suitable for Fireside. I suggest you plant a dwarf Honeycrisp, Freedom or McIntosh. All three of these apples are hardy, productive and would be suitable pollinators for your tree.

Question: I have a question concerning a blue spruce that I planted eleven years ago. The tree is about twelve feet high and six feet wide. The tree has sentimental value and I would like to move it to my new home. What is the best time to move this tree and what is the best method of transplanting?

Answer: Blue spruce, Picea pungens, has a shallow root system and is rather easy to move, but a tree this size must be moved with a tree spade (see yellow pages). September is probably the best time to move this species, but with a tree spade this species may safely be moved at other times including spring. For spring transplanting, I would move the tree as quickly as possible or before the buds start to elongate.

Question: I have window boxes on the south and east side of my house. What type of of flowers would you recommend for them? The east side gets lots of shade from a large tree and south side gets lots of hot afternoon sun.

Answer: Sun tolerant plants for the south side might include snapdragon, dwarf dahlia, geranium, marigold, petunia, zinnia, verbena, salvia, aegeratum, and wax begonia. Partial shade tolerant flowers suitable for window boxes might include snapdragon, coleus, Begonia, Impatiens, Lobelia, Browallia, Torenia, Vinca vine, tobacco, and ivy geranium.

Question: My mother-in-law has been looking for a plant called air fern. Have you ever heard of this plant, and if so, do you have any idea where I could buy one for her?

Answer: Air fern, also known as sea fern, neptunus, cypress moss, sea moss and aqua fern is neither a true fern or moss. Sertularia argenta, is the correct scientific name and what’s billed as “air fern” is the skeletal remains of a marine hydrozoan which has been died green. These “air ferns” have no roots or leaves and the green coloring will dissolve in water.

Most of these hydozoans are collected by trawlers in the North Sea and are sold as “curiosity or decorative indoor plants.” Every dime store used to stock these “plants” and from time to time I have seen them in various discount stores such as Wal-Mart and Lowe's.

Freedom, a disease resistant apple

(April 9, 2003)

Question: Of all of the apple varieties that will grow in this area, which one would you rate as most disease resistant?

Answer: “Freedom” is without a doubt the most disease resistant. This variety was developed in New York in 1985 and it has now been grown here long enough to remove it from the trial category. It appears to be quite hardy, vigorous and productive. This variety is a multi-purpose apple that is good for fresh eating, sauces, pies and juice. Maturity time is mid-October, and with proper storage the fruit will keep until January. Freedom requires no fungicide sprays, is immune to apple scab and is resistant to cedar-apple rust, mildew and fireblight.

Question: I know there are several types of dwarfing rootstocks for apples, but I wonder which one you think is best for this area. Could you also explain how far apart trees with this root stock should be planted?

Answer: M-26 is an excellent hardy dwarfing rootstock for this area. Trees on this rootstock are about 9-12 tall and 10 feet wide at maturity. In general, they are only 40-50% the size of standard trees. When planting, stake the trees for the first year and make sure the graft union is 2 inches above the soil surface. Trees on M-26 rootstocks should be planted 8-14 feet apart.

Question: I have a very old alpine currant hedge that has several dead areas. I have cut the hedge back to nearly ground level several times and I tried last year to replace some of the plants, but the plants don’t look very good. Is there some sort of spray I can use to rejuvenate the hedge?

Answer: Ribes alpinum, alpine currant, is a good hedge plant, but it is also susceptible to a number of diseases. Since your hedge is very old and beset with bare spots, I doubt that replacement plants or chemical fungicides or insecticides would solve the problem. I would recommend removing the hedge and starting over with something new.

Question: Last spring you recommend a type of redbud that is hardy for this area. Could you repeat that information?

Answer: The only redbud, Cercis canadensis, I would recommend is the Minnesota strain. These plants are grown from seed collected at the University of Minnesota Landscape Arboretum. Plants from this source will be available from the local established nurseries this spring.

Question: Last summer a friend of mine in the Twin Cities bought a house which had a beautiful yellow flowered honeysuckle in the garden. I have been unable to identify this variety and wonder if you might know what variety he has?

Answer: The most common and probably the best yellow flowered honeysuckle for the Twin Cities and this area is John Clayton honeysuckle, Lonicera sempervirens ‘John Clayton’.

Question: I have noticed that some nursery catalogs are selling potato “eyes”. Will these produce potatoes as fast as using the old method of cutting up chunks of potatoes? Also, is it really necessary to buy “seed” potatoes? I remember my parents planted left over potatoes from the year before.

Answer: Small potato “eyes” (buds) offered by nursery catalogs are usually a gigantic waste of money. These tiny buds are slow to develop because they lack a suitable energy reserve to get the plants started. Local nurseries are your best bet for potato planting stock.

Yes, certified, “Bluetag” seed potatoes are well worth the money. These plants are certified disease free. Home grown crops from last year are not.

Question: Do you have a web site or are your columns available on the internet?

Answer: Since February of this year, the organization, MAE or Mankato Area Environmentalists, has been kind enough to post my columns on the web at http://hickorytech.net/~enviros/dongordon.html.

Apple Maggot Control

(April 2, 2003)

Question: I have Haralson and Fireside apple trees that are about 10-12 years old. I get a good amount of apples on each tree, but I don’t think I had one perfect apple last year. The apples are all dimpled and deformed. I have been spraying every 7-10 days (weather permitting) with a general purpose spray (Bonide) that contains Captan, Malathion, Carbaryl and other ingredients. I feel certain that the damage is being caused by apple maggots, but what can I do to control these pests?

Answer: Apple maggots are the number one pest of apples in the Upper Midwest and without some method of control, one can usually expect a damaged crop. The first step in controlling apple maggots is to learn how to recognize them and to become knowledgeable of their life history.

The adult fly is somewhat smaller than the common housefly (about 1/2 inch long) and has clear wings with dark markings. The hind part of the body is dark colored with light bands. The adults may be present from mid-June, or slightly later in northern regions, through mid or late September, depending on the area and year. The flies lay their eggs under the apple’s skin. When the larvae develop they feed on the flesh.

These pest overwinter in the pupa form in the soil beneath apple, pear and hawthorn trees. Removing all dropped fruit helps in control, as does elimination of weeds. Chemical sprays such as the one you using are usually effective in controlling these pests, but timing, rate of applications and weather are all critical factors. Lots of rain when the flies are active may wash off the spray. County Extension offices have publications on recommended chemical sprays for apples.

Many organic gardeners, myself included, shun the chemical treatment and instead rely on homemade traps. These methods aren't 100% effective, but if used properly I have found they work well enough to produce more apples than we can ever use. These traps are pretty simple to construct and consists of small pieces of plywood painted yellow and croquet-sized balls painted red. Both of these are then sprayed with a sticky substance called Tangle-Trap. Details on how to construct and use these traps, plus a special trap used by Jackie Smith, Rodale’s Gardener of the Year, are too lengthy to repeat here, but they are in my book Growing Fruit in the Upper Midwest. Copies of the book are available from local libraries and area bookstores.

Question: I have had my roses in the same bed for more than 20 years. Now, I seem to be losing more than in past years. Is it advisable to go to the expense of starting with all new plants, or is it okay to move the old ones to a new bed?

Answer: For long term success, I would recommend starting a new bed with new plants. Many of the rose diseases are soil born, thus it would be difficult to move the old plants without also moving their pathogens.

Question: We are moving to Florida and would like to transplant a Clematis from our garden here. Would this plant do well in Florida?

Answer: The Clematis species and cultivars grown here are not recommended for Florida. Clematis is a rare site in Florida. The only species I have seen there is Armand Clematis, Clematis armandii.

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.