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Features (Gardening)

What you don’t know can kill a tree

Did you know that only roots less than one inch around are capable of generating new roots from the cut end? Did you know that the cut end of a small root can only grow three new roots at the most?
    Roots are not like branches. When you prune away the end of a branch, you stimulate the development of side branches. Root regeneration only occurs at the ends of the cut root.
    Root pruning is common in commercial nurseries where large trees are grown in the ground. Root pruning starts when the seedlings or rooted cuttings are first planted in the field, always after woody plants have stopped producing new leaves in the first flush of growth. It works to stimulate multiple branching of roots as close to the stem as possible so when the plant is dug and transplanted into your landscape, it will have a better chance of survival. Roots are typically pruned every two years with greater distance from the trunk each time.
    It’s done by making a circle of deep cuts at the plant’s drip line, severing the roots with a sharp spade.
    Root pruning during shoot elongation and leaf growth often results in severe wilting and loss of foliage, thus weakening the plant.
    However, there comes a time when the plants become too tall or wide and root pruning is no longer feasible. If root pruning were delayed until pruned roots are larger than one inch in diameter, many trees would die because large diameter roots are unable to generate new roots.
    So you take a risk when you decide to dig up a well-established plant to move it or cultivate a plant from a wooded area for transplanting into your landscape. Pruning away branches to achieve a balance between the top and the loss of roots only makes matters worse.
    Large roots can be stimulated to generate new roots by inserting toothpicks into the sides of larger cut roots. Soak wooden toothpicks in a concentrated solution of rooting hormone. Wearing latex gloves, use an icepick to pierce a hole in the side of the root and insert a treated toothpick into the hole. The rooting hormone in the treated toothpick will stimulate new roots to grow from the side of the large roots.

Native seeds need to cool down before sprouting

Seeds of native plants in the temperate region require chilling, called stratification, before they can germinate and grow seedlings. The acorn of the mighty oak must be stratified before it can germinate in the spring. But don’t go placing acorns in the freezer before planting.
    In nature’s cycle, acorns fall to the ground in the fall, while the ground is still warm and moist. On the ground, some are covered with leaves; some are gathered and buried by squirrels. Soon after landing, acorns begin to absorb moisture. Slowly, the ground cools. As soon as soil temperatures drop to near 45 degrees, stratification begins. When soil temperatures drop below freezing, stratification stops. As temperatures rise above freezing, stratification continues. Nature’s alternate freezing and thawing enhances germination.
    Each plant species has its own length of time for stratification. In species that grow over a wide range of latitudes, stratification periods can vary considerably. For instance, the red maple tree has a growing range from ­Quebec to northern Florida.
    The stratification period for seeds taken from trees native to Quebec is shorter than for seeds from trees native to northern Florida. This is because the ground freezes earlier and stays frozen longer in Quebec than in northern Florida. In northern Florida the soil seldom freezes hard, but it is cold enough that seeds germinating in early spring would be killed by frost. This phenomenon was verified when red maple seeds harvested from trees growing near Quebec were planted in northern Florida and seeds harvested from red maples originating in northern Florida were sown in soil near Quebec. The Quebec seedlings germinated in the middle of Florida’s winter and were killed by frost, while the seeds from Florida never germinated in Quebec.
    To artificially stratify seeds from our region, mix them with moist sand blended with some peat moss and allow them to absorb moisture for at least two weeks. Then refrigerate for another six to eight weeks before sowing. This is more or less following the normal daily temperature cycle.
    The lazy way of germinating native plant seeds is to sow them in the fall in a well-prepared soil with at least three percent organic matter. Cover the seedbed with a board to prevent winter weeds from growing. The seeds will undergo natural stratification.
    In the spring, at about the time the buds of trees are starting to show color, remove the board covering the seed bed and watch for seedlings to emerge.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.

Some bloom only in short days; ­others, only in long days

Did you know that in many plants, flowering — and bulbing — is based on the number of hours of exposure to light?
    This fact of plant biology explains many mysteries. Understand it, and you’ll be a smarter and more successful gardener.
    If you expose a chrysanthemum or poinsettia to more than 11 hours of light each day, it will never flower. The triggering mechanism that forces these species into flowering is exposure to no more than 10 hours of light. Those conditions of light are called short days and long nights. Interrupting their 14-hour night with even a flash of light can prevent flowering.
    During long daylight hours, greenhouse growers cover these species with shade cloths to force them to flower out of season. That’s why chrysanthemums are available throughout the year.
    Nature’s cycle of short days and long nights begins in late summer. This natural cycle enables us to enjoy fall mums and greenhouse growers to grow poinsettias without having to shade them.
    In the fall, some chrysanthemums flower earlier than others. This range is possible because breeders have developed cultivars with different maturing periods. Chrysanthemums’ short-day classification further divides into six-week, eight-week, 10-week and 12-week cultivars. These numbers refer to the number of weeks from the time a plant is exposed to 10 or fewer hours of light until the flower buds show color. By selecting different varieties, you can have chrysanthemums flowering in your garden for many weeks.
    Short-day woody plants include azaleas, rhododendrons, dogwoods, lilacs, spring-flowering roses and viburnums, to name a few. The flower buds on these plants are produced late summer and early fall for flowering in the spring.
    Long-day plants flower all summer long.  This includes bedding plants and woody ornamentals such as fuchsia, crape myrtle, hybrid-T and floribunda roses, some hydrangea and hibiscus, among others. When daylight hours fall under 10, the plants remain in a vegetative state of growth.
    Many varieties of onions are also classified as long- or short-day varieties. For long-day onions to form bulbs, they must be planted in the spring and form bulbs when the days are long. Short-day onions — as well as garlic — are planted in the fall and form bulbs when daylight hours are short. Plant short-day onions in the spring, and you’ll only get green onions.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.

Turn that manure into compost instead of applying it to fields

The new governor of Maryland has made a major error in allowing poultry farmers to continue applying their phosphorus-laden chicken manure on land that is already overloaded with phosphorus.
    What the chicken farmers and the governor are ignoring is scientific evidence that clearly identifies excessive levels of phosphorus in soils as the cause for phosphorus-induced trace element deficiencies, lower yields, lower nutrient values and Bay pollution.
    The smarter strategy is to grow soybeans one year then corn the next. Legumes like soybeans fix their own nitrogen and leave plenty in the ground to grow a crop of corn the following year. If this rotation were followed, farmers would only need to apply potassium when soil call for it. When the soil needs potassium, it can be added as either potassium chloride or potassium sulfate, both cheaper to apply than tons of chicken manure.
    Phosphorus is essential to plant growth. But too much causes other essential plant nutrients to bind to it, starving plant roots. Such essential trace elements as iron, zinc and copper are essential to plant growth, as are nitrogen, phosphorus, potassium, calcium and magnesium.
    In the mid 1970s I was asked by fellow University of Maryland faculty members who specialized in vegetable crops to review soil tests from fields of sweet potatoes near Salisbury. The total phosphorus levels in those soils were so high that they were reducing yields. I recommended they stop applying phosphorus and apply only nitrogen. This was a major change in culture for these farmers because they had been accustomed to applying tons of 10-10-10 before planting each season’s crop.
    So much phosphorus had been applied that it took several years with none before yields started to increase.
    In the early 1980s, rhododendron growers tried dosing their plants with lots of phosphorus to force them into flower under shade. It worked, but it also stunted growth and caused iron deficiency symptoms on the foliage. Full sun alone would have produced healthy tall plants with flowers.
    My conclusion from these and other studies is that plants do not need much phosphorus to be productive.
    Over-applying phosphorus not only leads to reduced yields and lower nutritional value. It also contributes to Bay pollution.
    Allowing farmers to make yearly applications of chicken manure on soils already saturated with phosphorus lowers yields of grain and forage crops. Since most of these farmers do not plant cover crops, their phosphorus-enriched soils erode into the Bay.
    There are other better uses for chicken manure, as compost or as a source of energy. The ornamental horticulture industry — the second largest agricultural industry in Maryland and the nation — is a ready market for quality compost. Yet Maryland has to import compost from as far as Maine to meet its needs. Maryland Environmental Services is well versed in the science and technology of making compost.
    Gov. Hogan, please encourage chicken farmers to form a co-op to manufacture and market compost.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.

Getting to the roots of woody plants

Did you know that when the stems of an oak tree are growing in the spring, the roots are not growing? Conversely, when the top of the plant has stopped growing and has stopped producing new leaves, the roots initiate growth. It’s the same with most woody plants. Most are unable to grow at both ends at the same time.
    In the spring, the stems and leaves are elongating and unfolding, while the roots are busy providing them water and nutrients. At maturity, the full-sized leaves begin sending down compounds such as carbohydrates, hormones and other metabolites used by the roots to produce new roots. In some plants, this cycle repeats itself. Many deciduous species will produce two or more flushes of top growth with brief periods of root growth. In other plants such as pine trees, there is usually only one flush of growth.
    Plants need to grow new roots because nutrients are absorbed only at the tips of roots. Nearly all nutrients are absorbed by root hairs, and these only occur on newly formed roots. As soon as new roots begin to form, the root hairs deteriorate, and that part of the root is covered with suberin, a sugar-like substance that enables the root to absorb only water.
    In other words, most of the roots of plants function as pipes, carrying nutrients and water to the stem when the tops are growing, then carrying metabolites to their own tips when roots are growing.
    This is knowledge you need to transplant trees and shrubs successfully. To assure better survival, growers root-prune plants a year or two before transplanting. To root-prune, make a circle of deep cuts at the plant’s drip line, severing the roots with a sharp spade.
    Wait until after woody plants have stopped producing new leaves in the first flush of growth. Root pruning during shoot elongation and leaf growth often results in severe wilting and loss of foliage, thus weakening the plant. Late-summer root-pruning has another advantage. More buds have formed, resulting in the maximum production of natural hormones that stimulate new roots.
    Annual plants are another story. In annuals, tops and roots grow simultaneously. This is possible because these plants have the advantage of growing only during long days and warm weather.
    Understanding root growth also helps you care for potted plants. Plants grown in containers have limited space for root growth. Keeping the plants in the same container for too long results in root-bound plants. There is no more room for roots to grow. Root-bound plants deteriorate or may flower profusely, wilt frequently and stop growing. Those are signs that it’s time to repot. When repotting, slash or tear apart the root ball to stimulate new roots to grow.

The underground story

Did you know that your bare garden soil is losing its nutrients to winter?
    That’s just what’s happening in your vegetable garden unless you planted a cover crop last fall. And in your flower garden, unless it’s planted with perennials or woody plants.
    Here’s the underground story.
    During the growing season, plants do not utilize all soil nutrients, whether applied as fertilizers or released from animal manures or compost. Nutrients such as nitrogen, potassium, magnesium and boron, to name a few, are quite soluble. Unless they are absorbed by roots of plants, they leach downwards into the water table, into streams and eventually into the Bay.
    A good garden soil is biologically active all year long except when soil temperatures drop below 34 degrees. At that temperature microbial activity stops, nutrients are not as soluble and most things stay in place. However, as you penetrate deeper in the soil, temperature rise and nutrients that have penetrated to that depth continue to leach downwards. Thus you want all soluble nutrients to be absorbed by roots before they seep too deep where roots do not penetrate.
    The physical movement of soil particles during periods of freezing and thawing causes soil particles to move about, creating crevices, thus facilitating the downward movement of soil particles as well as nutrients in solution. Established roots help to stabilize soil and prevent particles from either blowing away in drought or washing away through erosion. Both cover crops and perennials absorb available nutrients. When the cover crop is plowed or rototilled under in the spring, its roots, stems and leaves will decompose, and those nutrients, like compost, will be slowly released in the soil.
    While soil temperatures are above freezing, roots are absorbing nutrients. Roots of some species are capable of growing in soil temperatures as low as 36 degrees. Roots can grow all winter as long as the soil does not freeze. Unlike the top of plants, which stop growing when they begin to go dormant in late August and early September, roots continue to grow and absorb nutrients and water.
    I tested this concept in the mid 1970s by transplanting young dogwoods between the greenhouses at the University of Maryland in College Park. Half of the dogwoods were transplanted above a buried steam pipe. Snow there never lasted more than a few days, while between adjoining greenhouse the snow stayed in place. In the spring, I dug up the dogwoods in each area. The root system of the trees where the snow melted rapidly were two to tree times bigger and more fibrous than the roots of the dogwood trees from where the snow remained and were then five to six times larger.
    Never allow land to remain fallow without vegetation. Keeping the soil covered with growing plants not only protects the Bay but also maintains biologically productive soil for you to grow crops. Nutrients belong in the soil and not in the Bay.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.

Potted outdoor plants need cold-hardy roots to survive winter

Did you know that the roots of plants are not as cold-hardy as the stems and branches? What’s more, the roots of different plant species are killed at different temperatures. This is information you need to know when selecting plants for growing in above-ground containers that are to remain outdoors all year long.
    Below four feet, soil temperatures seldom drop below 28 degrees. If the ground is covered with mulch or snow, temperatures may be several degrees higher. If the soil is wet at the time it freezes, soil temperatures will also be higher. Dry soils freeze faster and achieve a lower temperature than moist or wet soils.
    In above-ground containers, temperatures will equilibrate to the ambient air within hours of a 10-degree change in temperature. The temperature change will occur faster if the rooting medium is dry. A dry rooting medium freezes faster than a wet rooting medium.
    If you intend to grow ornamental plants outdoors year-round in above-ground planters, select plants with cold-hardy roots. Choices are many, including Alberta spruce, Amur maple, azaleas, birch, chamaecyparis (or false cypress), mountain laurel, Pfitzer juniper, red cedar, rhododendrons and sumac.  The roots of these species can tolerate temperature down to zero and below. However, rooting media should be kept moist during the winter months as well as during the growing season.
    Avoid planting Atlantic cedar, boxwoods, camellia, Chinese hollies, Colorado spruce, dogwood, Japanese hollies, magnolia and viburnums in above-ground pots. Some of these species have roots that are killed at temperatures as high as 24 degrees. In many years, the roots of these species will be killed before the holidays.
    Information on low root-killing temperatures of perennial plants is important when selecting plants for containers and rooftop gardens. On rooftop gardens the problem is not as severe if the garden is installed over a heated building, because heat loss through the roof is generally adequate to prevent rooting media from freezing. However, if the garden is being installed over an unheated parking garage, selecting plants with cold-hardy roots is of utmost importance.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.

Knowledge makes power

The horticultural green industries — nursery, landscaping and greenhouse crops — are the second largest agricultural industry, second to poultry in Maryland and third in the nation. With home gardening the number one hobby, it is no wonder that the demand for trained horticulturists is so high.  
    Gardening is therapeutic, and those who partake in it realize great satisfaction from watching plants grow as well as enjoying the flowers, fruits or vegetables they produce.
    Nowadays, gardening is no longer limited to backyard plots. More than 80 percent of plants are grown in containers on decks, patios, balconies and windowsills or under artificial lights. Plastics have made it possible to design and manufacture containers that resist freezing and provide good drainage while looking attractive. Soilless light-weight rooting media, packaged in convenient-sized bags or boxes, are weed-free and engineered to satisfy the growing needs of most plants. Some containers can even keep the rooting media moist for several weeks.
    Advances in fertilizers in both organic and inorganic forms make it possible to limit the need to apply fertilizer on a timely schedule. Slow-release fertilizers are balanced to supply the needs of each nutrient based on well-established research.
    Greenhouses for home use were once expensive to build and maintain because they were covered with glass that was frequently broken by accident or by hail. Today’s small home-type greenhouses can be built inexpensively and covered with double-layer polyethylene or composites that can be shaped using a box cutter. These greenhouses are easily heated. Some of the plastic coverings can be used for several years, while composites have been known to last 20 years or more. Greenhouses allow you to start your own transplants for the garden and can be used to grow winter crops such as short-day onions, spinach, lettuce, radishes and Swiss chard with minimum heat.
    Many home gardeners are now starting to use low tunnels, small hoops 18 to 24 inches tall and 24 inches wide, in their gardens or raised beds. The tunnels allow them to start growing plants at least one month earlier in the spring and extend the fall growing season by at least a month. Clear polyethylene covers the hoops and is anchored to the ground by soil.
    A new method called Aerogation Green Wall Systems even grows plants on walls. These plants are grown in containers mounted to the wall; air from the room is forced through the rooting media, cleaning the air of impurities while humidifying and oxygenating it.
    Horticulture continues to evolve. When I joined University of Maryland’s Department of Horticulture in 1962, 80 percent of all nursery plants were grown in the ground. Container plants were mostly grown in greenhouses in clay pots. The rooting media consisted mostly of sterilized soil and peat moss. Plants were fertilized mostly with dry fertilizers such as 10-10-10 or 10-6-4 or liquid 20-20-20 using a hose-on-nozzle. Greenhouses were covered with glass and heated mostly by steam or forced hot water.
    Horticultural technology has made many dramatic changes and created many opportunities. The demand for trained horticulturists is greater now than ever before. Anyone can dig a hole, but it takes a good understanding of plant science to grow plants efficiently, protect them from insects and diseases and use them properly.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.

Put these tools — not useless ­garden gadgets — under the ­Christmas tree

I hope you had a laugh over my column on useless garden gadgets two weeks back. This week I’m turning serious, suggesting useful tools the gardeners on your holiday shopping list will want and use.
    The Garden Bench and Kneeler is great, especially for us older gardeners. Getting down on your knees is easy; getting up is hard. The Garden Bench and Kneeler pad is easy on the knees, and the handles are a great help in getting up. I have had mine for years. When you get tired, turn the kneeler up and you have a bench to sit on.
    The Garden Stamp or Dibble Board is ideal for maximizing garden space as it provides the proper spacing for transplanting or sowing seeds. Different boards are made for different crops. Rake the garden smooth before pressing the board into the soil. Then sow seeds or transplant in the indentations made by the stamp. I have made them for my own garden using old broomsticks, dowels and scrap lumber.
    Gator Bags or Arbor Rain Bags are very effective for transplanting trees and shrubs and for keeping young trees alive, without wasting water, during drought. Installed around the base of newly planted trees or shrubs and filled with water, the bags release the water slowly into the soil for days so the root ball stays moist until new roots grow out into the soil. They’re also easy to fill.
    The Garden Weed Torch is a great way of killing weeds growing in the cracks of sidewalks, in gravel-mulched beds and along ditches without having to use weed killers. A quick flash from a flame kills weeds without damaging concrete or stones, and it doesn’t leave any residue.
    Okatsune Shears, made from the same process used for making Samurai swords, are great for cutting plants. Long handles make them easier to use.
    Pruners and loppers by Felco and Corona keep their cutting edge with very little sharpening. For pruning branches eight to 12 feet above your head, use long-reach pruners. Carry hand pruners in a sheath attached to your belt to prevent injury.
    The Soil Knife is a great tool for dividing perennials, for digging holes when transplanting and for lifting seedlings from the soil. Mine is a Japanese gardener’s knife with a blade about two inches wide and cupped for digging, so it can be used in place of a trowel for planting. One edge of its blade is saw-toothed, while the other can be sharpened. Also purchase the sheath for carrying it.
    Soil thermometers are useful in determining when to start planting certain crops. For instance, corn seeds should not be planted until after the soil is 60 degrees or warmer. A long-shank thermometer is helpful in monitoring microbial activity in compost piles. An active compost pile should read 130 to 140 degrees. When temperatures drop below 100 degrees, it is time to turn the compost.    
    The Weed Stick and Weed Wick are safe and effective for applying herbicides with minimal environmental impact. The Stick and Wick apply the herbicides only in a limited area, thus preventing potential problems associated with sprays. Apply the chemicals based on manufacturer’s recommendations.
    The Weed Bandit hoe is my favorite because of its long rake handle and stainless steel head with a corrugated blade that stays sharp. I like the small Weed Bandit for hoeing onions and closely planted plants, and the medium blade Weed Bandit for all other weeding work.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.

Decking your halls, from trees to poinsettias

Buy a Fresh, Safe Christmas Tree
    For the freshest Christmas trees, buy locally from a Christmas tree grower’s lot or cut your own. Otherwise, you could be buying an imported tree cut in late October or early November.
    Fresh-cut Douglas fir, Scots pine and blue spruce are the most fire-safe Christmas tree species, ranked by the State Fire Marshal based on research conducted by the Bay Gardener in cooperation with the Maryland Christmas Tree Growers.
    Fraser firs are not fire safe. Do not buy them.
    Once you bring the tree home, cut an inch from the bottom of the trunk and place in a bucket of 100-degree water. Keep the tree and bucket in the shade until you are ready to bring it indoors. When you bring it in, cut another inch from the trunk and immediately place it in water. Make certain there is always water in its stand. A good Christmas tree stand should hold at least one gallon of water.

Wreaths and Roping, Too
    Most of the Christmas wreaths and roping sold in big-box stores, grocery stores and many garden centers are made in New Mexico, North Carolina, New Jersey, the West Coast and Canada starting in October. Few of these facilities have climate-controlled cold storage for keeping greens fresh prior to shipping. Most are stored on the floor in sheds and barns and sprinkled with water when they appear to be drying. By the time they reach Maryland, they have already lost a high percentage of their moisture.
    At Upakrik Farm, I wait to make wreaths and roping until Thanksgiving week to assure freshness. I store them on the barn floor in stacks no greater than 10 deep to prevent compression and to assure adequate moisture. I sprinkle the wreaths and roping daily to keep them moist and cool to maintain freshness. Because I sell only freshly made wreaths and roping, I have many repeat customers at the Riva Road Farmers Market. There is no substitute for freshness.

Gather Greens in Your Garden
    For long-lasting holiday greens, gather arborvitae, Canaan fir, Douglas fir, junipers, Nordman red cedar, red pine, Scots pine and white pine. Many broadleaf evergreens will also hold up throughout the holidays. Choose from American holly, cherry laurel, Chinese holly, English holly, English ivy, mountain laurel, pachysandra, periwinkle, rhododendron and southern magnolia.
    Increase the life of greens by cutting one to two inches from the base of the stem as soon as you bring them indoors and immerse them in 100-degree water. Change the water at least every other day.

If You’ve Got Winterberry Holly, Bring It In
    Winterberry shows at its best this season, inviting you to cut it for Christmas decorating. The native deciduous forms of holly grow as shrubs six to eight feet tall. At this time of year, the ends of the branches are filled with clusters of bright red berries.
    Use extreme care when cutting the stems to minimize shedding berries from the stem. Once they are cut, do not put them in water. Since the berries shrink very slowly, they will remain attractive for a month or more indoors. Thus, they’re ideal for making dry arrangements or for decorating the Christmas tree.
    Holly berries are not poisonous, though neither do they taste good.

Keep Poinsettias Pretty
    The brightly colored bracts and dark green leaves of poinsettias make them the ideal Christmas plants. Varieties are better now than ever before. Now available in many shades of red, white, pink and speckled, they retain their bracts and leaves longer with minimal care.
    And no, they are not poisonous.
    Keep your poinsettia fresh looking by careful watering. Check the growing medium daily for adequate moisture by pressing your finger into the medium halfway between the stem of the plant and the wall of the pot. If the medium feels cool and moist, there is adequate moisture. If the medium feels warm and dry, water thoroughly.
    Add water until it flows through the bottom of the pot. If water flows immediately through, the medium is too dry to absorb water. Soak the pot in a basin or pail of warm water for 30 minutes to an hour. Drain the plant before returning it to its place.
    Avoid overwatering. Poinsettia roots are very susceptible to rot.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.