Plastic Recycling Facts

Plastics have astonishing strength, structural designs, and excellent recycling features. There are plastics that are recyclable and there are non-recyclable. Scrap or waste plastics can be reprocessed into useful products such as bags, microwave dinnerware, chairs, tables, decorations, furniture, medical equipments and other variety of objects.
The plastics are made up of polymers which include:

1. Polyethylene terephthalate (PET) used for beverage containers such as bottles for water, soft drinks and salad dressing, as well as in clothing industries.

2. High-density polyethylene (HDPE) used in contact with food such as milk bottle, juice bottle and bottle for organic solvents. It can also be used for trash bags.

3. Polyvinyl chloride (PVC) used in houses for making linoleum on the floor, vinyl car tops, raincoats, shower curtains, and water pipes.

4. Low-density polyethylene (LDPE) used for packaging, e.g. foils, trays, frozen food bags andor plastic bags, and squeezable bottles for food and non-food purposes. It can also be used as protective coating for paper, textiles and other plastics.

5. Polypropylene (PP) used for microwavable dinnerware, margarine tubs, and disposable cups and plates. It can also be used in ropes, carpets and thermal under wares.

6. Polystyrene (PS) or Styrofoam used for egg cartons, disposable plates and cutlery, and for safe shipping of fragile products. It can also be used as packaging material to preserve hotness or coldness of beverages from cups.

Plastics are categorized according to their resin identification code in which polymers are being identified. Through uniform identification of codes to polymer types, recyclers could easily classify plastics according to their resin types. Plastic recycling have different ways and different uses. The code provides plastic recycling to be economically feasible.

Nowadays, plastics are being recycled not only for business purposes but also for environmental reasons. The more plastics you recycled, the more money you saved, and at the same time, the more you contribute to the environment. Compared to wood, paper, cardboard, glass and metal, plastic recycling are somewhat complex since it requires extensive processes because of the intermolecular forces of attraction between polymer chains.

One way for effective and efficient plastic recycling is through the use of dyes and fillers that are commonly utilized in beverage bottles and plastic bags, thus recycling is much easier and most preferable in this way. Plastics have strong construction and long-lasting characteristics to which production of new, reusable products will result to provide less permanent and durable products than the original.

Speaking of cleanliness, many producers are further researching for biodegradable plastics while others are thinking that most plastics would contribute as waste materials that will create destruction to our environment. But they don't realize that plastics can be recycled for human needs, thus helpful in preserving the Mother Earth. Collecting products, e.g. plastic bottles, out of our garbage cans and even in our landfills, and identifying their polymer types, are best practices for effective recycling. From time to time, plastic recycling become a source of income without causing damage to the environment.

POTATOES IN POTS AND OTHER APRIL GARDENING TIPS

Planting potatoes in large tubs or pots, removing strawberry mulch, and dividing rhubarb are some of the gardening activities for this month.

If you don't have room to plant potatoes in the garden, try planting them in tubs or large pots. Using chicken wire or wire mesh, fashion a cylinder that's about 3 feet tall and 3 feet in diameter and place it over a tilled bed. Place a layer of hay along the inside walls of the cage, then add a 2- to 3-inch layer of rich garden soil and plant 4 potato tubers. Cover the tubers with more soil. As they grow, continue lining the inner edge of the cage with hay and covering the young sprouts with soil until you reach the top of the cage. Keep the plants well watered and harvest when the vines naturally die back.

Another method is to buy one of the relatively new black potato bags—a heavyweight fabric bag that is somewhat porous, and holds about 15 gallons of soil.  Fill it about a third full of soil mixed with compost, then gently press the seed potatoes in near the top.  If large potatoes, cut them in half or pieces such that each one has at least 2 or 3 healthy emerging shoots or “eyes”.  Then once the plants begin to grow, add more soil until the bag is eventually about full.  Start your potatoes indoors now in a bright, somewhat warm location, then move them outside later in spring after frosts.  This way you can harvest potatoes by mid-summer.

Check strawberry plants twice a week for signs of new growth. As soon as you see sprouts, remove the hay or straw mulch and spread it in the rows to help control weeds. A topdressing of an inch or two of compost will give plants a boost.

If your rhubarb plants seem crowded, plan to divide them as soon as the ground thaws. Choose a cloudy, cool day, dig up the whole crown, and break off the young side shoots, trying to keep as many roots intact as possible. Transplant the mother plant back in the original hole amended with a shovelful of compost, and plant the babies in a full sun location. Harvest the young plants lightly, if at all, the first year.

Don't rush into the garden to till; wait until the soil has a chance to dry out. Tilling too early can cause soil compaction and poor growth later in the season. To know when to till, do a squeeze test: grab a handful of garden soil and squeeze it -- if it drips like a sponge it's too wet to till.  It should form a ball in your hand, then crumble when lightly squeezed.

Spray horticultural oil on fruit trees such as apples, plums and cherry to smoother any overwintering insects. Choose a calm day when temperatures are above 40 degrees (F), and be sure to cover all sides of the branches. You can also apply it to evergreens to control spider mites and other insects -- carefully follow the instructions on the label for proper usage and appropriate plants.

Once the snow melts you may start to see browning damage on lawns from road salt. To help flush the salt from the soil, water the lawn near roads and walkways several times, especially during dry periods. This will help move the salt down into the subsoil. Once this salt is removed, then you can begin to prepare the thin spots in the lawn for reseeding.  

Charlie Nardozzi, Horticulturist and
Leonard Perry, UVM Extension Horticulturist 

http://perrysperennials.info/articles/apr11tips.html

SPRING CLEANING THE WATER GARDEN

If you have a water garden, other than a large pond, spring is the time to evaluate if it needs cleaning, and to do so then before life in it fully resumes.  If there is sediment build up on the bottom (a half inch or more) and leaves floating on the top, and the water is murky, cleaning will help keep fish healthier and unwanted algae from growing. 

Evaluate your water garden after spring thaw occurs. If you have been diligent about pruning plants and skimming, you'll only need to drain the pool or pond every three to five years. If you like pristine clear water, then cleaning yearly may be needed.  Never drain it more than once a year, however, and ideally when temperatures are below 55 degrees F.   Water gardens have beneficial bacteria that keep algae in check, and below this temperature they aren’t yet established.  Cleaning out the water when warmer may disrupt this balance, with the water going “green” before the bacteria build again to sufficient numbers.

If you have a simple plastic tub with no fish as I do, you can simply drain and clean it, before refilling.  I just use a pail to get most the water out, then a plastic dust pan, scoop or old sponge for the rest.  If you had any plants left in over winter, remove them to a place out of sun and keep moist (a tray or pan with water works well, or moist newspapers over the top) for the short time you’ll need for cleaning.  If you had water plants that love warmer temperatures, and didn’t hold them over winter indoors in pans of water over 50 or 60 degrees F, they may need replacing.
 
Depending on the amount of decomposed debris, you probably can use a net to clean small pools. For larger ponds, or where a lot of debris has settled at the bottom, you will need to pump the water out with an existing or submerged pump, or by siphoning. If you have small fish, place some screen over the hose or pump to keep them from being sucked out.  You can transfer most of the old water to a clean garbage can, children's wading pool, or large buckets to be used for watering plants.  Or, merely water lawns and garden beds with the nutrient-rich water.

As you lower the water level, carefully remove the plants. If you have fish in your pond, pump the water level down to about six inches, then catch them with a net. Put the fish in holding containers of the "old water," covering these with netting to discourage predators, and if koi to prevent them from jumping out. Keep fish out of direct sun, and get your cleaning done soon so they can be reintroduced the same day.  They’re weak after a long winter, so you want to minimize stresses on them.

Once the pond is empty, quickly rinse the walls. Some prefer to use a forceful nozzle on a hose, rather than pressure washer, to try to leave some of the algae on the sides and rocks.  This will help your pond “ecosystem” reestablish more quickly.   If you have rocks and gravel buried in sediment, you may need to remove them and clean out the sediment before replacing.  With the water out, check liners and hoses for leaks and repairs, and clean or replace filters. 

After washing, pump the remaining water out, or use a wet/dry shop vacuum.   Then refill with clean water, adding a neutralizer chemical (according to label directions), if you have fish, to hasten dechlorination. If you did a thorough cleaning, or did so during warm temperatures, you may want to jump start your beneficial bacterial with a commercial microbe product. 
          
Replace the plants, giving those that need it a trim first, repotting or dividing them if the pots are bursting at their seams. You can add fertilizer to pots, granular mixed with the soil or special pond tablets pushed into it.  If you have fish, use fish-safe fertilizer pellets.

When the water temperature stabilizes, you can return the fish to the pond.  Check first to make sure they are healthy, with no visible signs of disease or parasites, in which case you’ll want to quarantine them.  There should be no more than a three to five degree difference in temperature between the old and the new water to prevent shock to the fish.

It's a good idea to add some hiding places for fish and frogs in the pond as a guard against predators. Pond walls that slope straight down from the sides, as opposed to gradual slopes with shallow areas, which wading birds like, also help prevent predators from cleaning out your fish.  An owl or heron decoy placed near the pond may help, just remember to move it often to simulate the real thing.

Plants will keep water clear as they absorb the nitrate buildup that naturally occurs in ponds. However, throughout the summer, you will need to regularly prune plants both to control algae and enhance the appearance of the water garden. One rule of thumb is that the pond surface should be 60 to 70 percent filled with plants, maximum.  Periodic skimming and netting also will keep your water feature attractive, and minimize spring cleaning next year.

Follow these steps and your water garden will be a low-maintenance and beautiful asset to your landscape, not a high-maintenance eyesore.  Check local complete garden centers for plants and supplies. A directory of suppliers, plus information on all aspects of water gardening, can be found online (www.iwgs.org).  

Dr. Leonard Perry, Extension Professor
University of Vermont 

http://perrysperennials.info/articles/sprwater.html

FERTILIZING LAWNS

Fertilizer is essential for good lawn growth, yet with good lawn management and soil testing you often can reduce the amount needed.  Soil test kits are available from state Extension Services, and include instructions for proper sampling.

Testing your soils every three years or so is a good practice. A key component of a soil test is the soil acidity, or pH.  If this is not between 6.0 and 7.0 (the latter being neutral, between acid and alkaline), certain nutrients won’t be available to the lawn, no matter how much you apply. 

If available, have your soil organic matter tested too.  It should be above three percent.  If lower, you should sprinkle compost heavily (up to half inch) over the lawn a few times during the season. Make sure the compost is aged, and free of weed seeds.

Mow more frequently to avoid having an excess of grass clippings so you can leave them on the lawn.   This simple practice recycles nutrients back into the soil, and has been shown in research at the University of Connecticut to reduce fertilizer needs by 50 percent or more.

In Vermont and similar cold climates with shorter growing seasons, fertilize lawns in late April, early summer, and then late summer.  If you leave grass clippings, and have good organic matter in the soil, you may need to only fertilize twice—early spring and late summer. At each application time, you should apply one pound of actual nitrogen for every 1000 square feet of lawn.  The key words here are “actual nitrogen”, not pounds of fertilizer.  Of the three numbers on a fertilizer bag, the first is percent nitrogen.  So a 5-3-4 fertilizer has five percent nitrogen.  To figure how much fertilizer will give you one pound of nitrogen, divide one by the first number (one divided by five is 0.2), then multiply by 100.  So 20 pounds of 5-3-4 will yield one pound of actual nitrogen.  If you have 5000 square feet for instance, you’d need five times that, or 100 pounds of fertilizer, evenly spread over the area.

Apply fertilizer with a fertilizer spreader. Spreading fertilizer by hand will always cause some spots to be over-fertilized and others to have none. When using a spreader, be sure to get complete coverage of the lawn. Keep moving at a constant speed to prevent uneven spreading. Any missed spots will appear quite yellow. Do not fill the spreader when it is sitting on the lawn. Fertilizer spills are inevitable and may cause a large dead spot that persists for weeks.

Use caution when applying fertilizer combined with herbicide, especially with broadcast spreaders. These spreaders can throw the material into flowerbeds where the herbicide can injure desirable ornamental plants, or tree and shrub roots can pick these up from under lawns.

Lawn fertilizers vary in composition and price. An ideal composition for a chemical lawn fertilizer is a 4-1-2 ratio of nitrogen, phosphorus, and potassium, for example 20-5-10. Many others created for lawns, that may not be this exact ratio, will work fine too.  For a natural fertilizer, a 3-1-2 ratio is good, but anything close such as a 5-2-4 fertilizer works fine. 

The price of the fertilizer relates somewhat to the analysis and the nutrient carriers used in the fertilizer. Less expensive chemical fertilizers are usually water soluble, thus have a high potential to burn the grass if applied when hot, at high rates, and not watered in after spreading.  Being water soluble they are easily leached out of soil with rain and watering, so may pollute water sources.  Yet water-soluble fertilizers will give a response for four to six weeks, become available in the spring when temperatures are still cool, and result in more and darker growth sooner.  If overfed with such fertilizers, succulent grass growth may be more susceptible to insects and diseases.

More expensive fertilizers are not water-soluble (often seen as WIN for water insoluble nitrogen), have low burn potential, and give a response for up to eight weeks, or longer. These fertilizers rely on microorganisms in the soil to release the nutrients. Since the microorganisms are not active when the soil is cool, the fertilizers will not become available early in the spring. Not being water soluble is the reason they stay around longer, and so have less potential for pollution from runoff.  Many good lawn fertilizers will have a mix of both water soluble, and water insoluble nitrogen.  Where lawns are watered regularly, especially on sandy soil, these water insoluble fertilizers should be used.

Many natural-based fertilizers are water insoluble, so last for a long period.  Such natural-based or organic fertilizers have other benefits, such as aiding soil microorganisms needed for healthy soil.  These various forms of soil life provide many benefits, including converting nitrogen from the air for use by plants, producing carbon dioxide which plants need, dissolving nutrients from minerals in rocks, decomposing thatch, aerating the soil, and helping to reduce pests and diseases. So in spite of lower numbers (percent of nutrients) on the bag than with chemical fertilizers, these natural fertilizers enrich the soil in many more ways than the chemical fertilizers.  

 Dr. Leonard Perry, Extension Professor

University of Vermont

http://perrysperennials.info/articles/lawnfert.html

AN EASTER BASKET OF FLOWERS

The flower that most often comes to mind when we think of Easter is, of course, the Easter lily. But there are other flowers appropriate for this time of year as well, all with rather interesting origins.

In the Alps, the narcissus has been associated with Easter for centuries. In fact, even before Christianity, the narcissus represented springtime in Greek mythology.   It is still widely used as the main Easter flower in many countries. 
In England and Russia, pussy willows are used for Easter flowers. In the Middle East, it is wild tulips, while in Mexico, tropical flowers fill the churches during this spring holiday season. The early Germans decorated with red flowers and red fruited plants such as English holly, believing the red color represented the blood of Christ. The field anemone (Anemone coronaria) also was associated with the passion of Christ.

The Easter cactus (Hatiora gaertneri, formerly Rhipsalidopsis), is so named as this relative of the Thanksgiving and Christmas cacti, all looking almost identical, blooms in spring.  The funnel-shaped, flaring flowers are either rose purple or scarlet orange, coming out of flat, segmented leaves.  These, as their kin, are often found in hanging baskets where they’re well adapted, growing naturally on trees in Brazil.  The flowers open during the day, closing at night.  Being a cactus, keep this one on the dry side.

Do you know the Bermuda lily?  You probably do, as this is the true name of the Easter lily, deriving from its origin.  It is a pure white flower, believed to symbolize purity. Coming from one bulb, the flower is said to represent the tomb of Jesus with the blossoms symbolizing his life after death.  It is the most common flowering potted plant of spring.

When buying a lily, select a plant with many unopened buds and leaves all the way down the stem. Poor growing conditions or root disease will cause the loss of leaves from the bottom up, so be sure to pull back the wrapper to check.

Choose a well-proportioned plant, one that's about two to three times as high as the pot. Check the buds, flowers, and leaves--especially the undersides--for signs of insect pests and disease.  

To keep your lily healthy at home, remove the decorative foil or paper covering the pot, or make a hole in the bottom, to allow better drainage. Put your plant where it will get plenty of bright, indirect light and cool temperatures. About 40 to 50 degrees F at night, or as cool as possible, and below 68 degrees F during the day is ideal.  

You also will need to keep the soil constantly moist. To prolong the life of the blossoms, remove the yellow, pollen-bearing pods or anthers found in the center of each flower as it opens.

Don't expect your lily to flower again as it's already been "forced" once by the grower to bloom in time for Easter. However, you might get your lily to bloom again next fall by planting it outdoors once the soil has warmed up.  

If you plan to replant your lily outdoors, remove the flowers as they fade. Put the plant on a sunny windowsill for four to six weeks until the foliage matures. Continue to water.  When the leaves turn brown, cut the stem off at the soil line. Then in late May, plant the bulb four to six inches deep in a sunny, well-drained location. Fertilize twice during the summer. With luck, your lily will bloom this fall. Just don't count on it surviving a northern winter. 

Other appropriate flowers for Easter, and spring in general, are other bulbs such as tulips and hyacinths, and azaleas.  The bulbs can be purchased as cut flowers, or in pots.  If potted, the hyacinths can be planted outside in warmer weather, and may survive to future years.  Most tulips, however, will not come back next spring.  If giving the hyacinth as a gift, make sure the recipient isn’t allergic to the strong odor of the flowers.
           
Azaleas come in reds, white, and pinks.  They are tender, so wont survive winter outdoors in northern climates.  Still, they are a good value.  Keep them moist (not wet), and cool with plenty of light, and you should get several weeks of blooms indoors.  

Dr. Leonard Perry, Extension Professor
University of Vermont 

http://perrysperennials.info/articles/basket.html

COLD CLIMATE FRUIT TREES

For every climate there are certain fruits that grow better, or may not grow at all.  Even a fruit like the apple, that grows in all states, has cultivars (cultivated varieties) that grow better in certain regions.  Buying from local nurseries in the spring is one of the best ways to be assured that the fruit selections are adapted to your particular area.  When shopping online and through mail-order catalogs in winter and spring, make sure what you want has a chance to succeed in your garden.  There are quite a few tree fruits to consider for colder climates.

           

Apples are arguably the most common tree fruit in cold climates, perhaps because they are the hardiest.  This comes from both the cultivar and the rootstock onto which this is grafted.  Unless you order from a specialty grower, you don’t need to worry about which rootstock is best as the nursery has already done this.

For cold climates, such as the northeastern states, you’ll want cultivars such as McIntosh that ripen best with warm fall days and cool nights.  Some of the most hardy cultivars (USDA zone 3, or -30 to -40 degrees F average minimum winter temperature) include Honeycrisp™, Honeygold, Lodi, Northern Spy, and the relatively new Zestar!™ from the University of Minnesota.  There are several other apples hardy to zone 4 (-20 to -30 degrees F) including Cortland, Empire, Freedom, Gold and Red Delicious, Liberty, Paula Red, Red Rome, and Spartan.  Several heirloom cultivars to consider are Cox Orange Pippin, Gravenstein, Wealthy, and Yellow Transparent.

           

Peaches are one of the tree fruits that many gardeners want to grow, but unfortunately few are adapted to the coldest climates.  Most are hardy only to USDA zone 5 (-10 to -20 degrees F) at best, nectarines (smooth skin peaches) even less hardy.  Even if they grow they may not fruit, having flower buds damaged at higher temperatures than leaf buds.  Flowers may be damaged by spring frosts, especially common with apricots. Even a short mid-winter thaw may cause buds to lose their hardiness.  Peach trees also need a long growing season to harden off for winter, and to develop next year’s buds, something they may not get in cold climates. 

           

An eastern exposure is best for peaches and their relatives, warming sooner on cold spring days so less prone to frost damage.  Proximity to bodies of water helps moderate temperatures too.  Those cultivars that may grow into zone 4 include Canadian Harmony, Contender, Glohaven, Madison, Red Haven, and Reliance-- perhaps the most cold hardy and popular northern peach, an introduction from the University of New Hampshire.

           

Most European pears are a bit hardier (usually to zone 5) than peaches but less so than apples, so they may not all grow reliably in the coldest climates.  Asian pears in particular are best in warmer climates.  Among the hardiest European pears, perhaps even into zone 3, are Flemish Beauty, Luscious, Parker, and Patten. 

While sweet cherries are generally only hardy to zone 5, many sour cherries grow into zone 4.  If you want to try sweet cherries, those possibly fruiting into zone 4 include Kristin, Stark Gold™, and the Cornell University introduction WhiteGold™.  

Sour cherries come in two types.  The amarelle type includes the common pie cherry Montmorency, with fruit flattened on the ends, generally bright red or yellow inside, and producing a clear juice.  The Morello sour cherries such as Marasca (from which the Italian liqueur and maraschino cherries are named), have rounded fruit, bright red inside, and produce a dark juice.  Among the most hardy sour cherries to zone 3 are Meteor (amarelle) and North Star (Morello).  Surefire™ (Morello) from New York state is late blooming, so better resists frosts. 

           

While the European plums are generally hardy to zone 5, and the Japanese to zone 6, the American hybrids are hardy to zone 4 and sometimes to zone 3.  For the coldest areas, also consider hybrids of cherries and plums called cherry-plums in the U.S. and chums in Canada.  One of the main problems growing plums in the north is that they bloom a week or two ahead of apples, so may be damaged by spring frosts. Empress and Shropshire are cultivars that bloom later, so may miss these frosts. One of the hardiest of the European plums, Mount Royal, came from Quebec in the early 1900s.  The hardiest American hybrids include Alderman, Superior, and Waneta.

           

In addition to hardiness, at least three main considerations apply to choosing any tree fruit.  Pick ones you like to eat, and usually buy from markets.  Also pick ones for your space and needs.  Dwarf and semi-dwarf trees are popular as they take up less space, and bear sooner than standard size trees.  Many cultivars of tree fruits are better suited to certain uses—eating fresh, cooking, sauces, canning or freezing, or making juice—so determine how you might like to use them.  Apples for eating fresh are often called “dessert” apples.

           

When buying tree fruits, it’s always best to get at least two different cultivars that bloom at the same time for cross pollination.  Even though some may be listed as “self-fertile” (if you have only room for one tree, look for these), they invariably fruit better with a partner nearby (within 50 to 100 feet).  Peaches, however, generally don’t need such cross pollination.

Dr. Leonard Perry, Extension Professor

University of Vermont

http://perrysperennials.info/articles/coldfruit.html

PRUNING FRUIT TREES

Especially for young trees just planted last year, late winter and early spring is an essential time to prune.  As trees are dormant, not yet growing, this is usually called "dormant pruning."
           
If you remember nothing else, keep in mind the 2 C's and 3 D's.  Remove any crossed and crowded branches, and any dead, diseased, or damaged.  Crossing branches rub on each other, wounding bark and allowing diseases to enter.  Crowded branches keep light from getting to the inside, so you won't get as many leaves and fruit, and may get more diseases instead.  For older trees, the adage is that a bird should be able to fly through the tree without interference.
           
Dead branches are obvious in the growing season, but this time of year with no leaves you'll need to look for ones off-colored, often with shrunken (canker disease) areas.  When pruning damaged branches, prune back to just above a bud, to a lower branch, or back to the trunk.  Where older branches come off the trunk they form a raised area or ridge of bark.  Cut back to, but not into, this bark ridge or "collar."
           
Another important point with many fruit trees is the branch angle, as measured at the base, from the trunk.  Those mostly horizontal, usually a bit under 90 degrees from the trunk (a right angle), are the strongest and bear the most fruit.  Those upright, especially at an angle less than 45 degrees from the trunk forming a V-shape, have what are called narrow crotches (where the branch meets the trunk).  These are are vigorous, produce less fruit, and are prone to breaking in wind and winter ice. Branch angles even may vary among cultivars of a fruit type, such as Delicious apples growing more upright, and Jonathan being more spreading.
           
You have a couple options for such branches, one being to prune them off at the trunk.  If the tree is young, and the branches are where you'd like them, they can be "spread".  If real young, only a few inches long, push them downward using a clothespin clamped on the trunk.  If they're a bit longer, even a year or two old, hold them downward for a season with wood stakes (with a cut off nail on each in), or by hanging weights (fishing weights for small branches, cement weights the size of small drink cups for larger branches). 
           
There are three main pruning systems that are used for fruit trees-- the central leader, modified leader, and open center or vase shape.  The central leader is just that--one main branch reaching upward, the tree forming a conical or Christmas-tree shape.  It is often used for upright trees that don't get too tall like dwarf or even semi-dwarf apples, or European pears and plums.  If you don't mind standard size fruit and nut trees reaching a full height, often 30 to 50 feet (more for most nuts), then the central leader system is for you, or rather them.
           
On the other hand, if you want to keep upright trees such as many apples, upright sour cherry cultivars, and European plums (some of the latter are hardy into USDA zone 5) lower, then prune these to the modified leader.  This is like a central leader early in life then, when at the height you want, prune out the main leader and allow main side branches ("scaffolds") to develop.
           
When selecting which scaffolds to leave, they should be equally spaced around the tree, none directly and closely above another.  For dwarf trees, as you measure up the trunk, scaffolds should be about a foot apart, about two feet apart for standard trees, a distance in between for semi-dwarfs.

For some trees you may want to use a variation of the modified leader-- the multiple leader system.  It is a cross between the modified and the central leader.  Once the tree is tall enough for you to manage or as you desire, prune out the leader but allow several upright (not horizontal) branches to develop.  This is often used for European pears; in case the fireblight disease attacks one or more leaders, there will be others left.
           
The final system is the open center or vase-- descriptive of the shape.  This is used for spreading trees such as peaches (where they can be grown, most aren't hardy even into zone 5), filberts, spreading sour cherry cultivars, and American plum hybrids and their species.  For an open center, to allow full light to enter the center, don't let a central leader develop.  From an early age of the tree, prune to have 3 to 5 main scaffold branches.  Then each year in late winter or early spring, prune off any upright shoots in the center of the tree.  Prune upright shoots farther out on the scaffolds back to a bud pointing outward.  This will keep the tree growing more horizontal then vertical.
           
A couple other rules are useful when pruning fruit trees.  The more you cut off, the more growth this stimulates.  So if you want to slow down growth on a vigorous tree, don't prune it as much.  Pruning in summer can help this way too, as pruning then results in less regrowth than dormant pruning.  Just don't prune after midsummer, so any new growth can harden by fall.

Dr. Leonard Perry, Extension Professor
University of Vermont

http://perrysperennials.info/articles/prunefrts.html