Start with healthy material, and keep it away from your other plants until you’ve been able to thoroughly inspect leaves, branches and soil for obvious pests.
 

• Proper material (be aware of plant health and zonal compatibility);
• Proper potting and siting, including right combination of exposure to and protection from     the elements (light, temperature, humidity, ventilation, animals and other things that bump);
• Proper watering and feeding (frequency, quality and quantity -- also using appropriate soil mix);
• Proper pruning and shaping (timing and amount).

        Clean and sterilize tools and pots (and accessories) after use.

        Better to discard old soil than re-use it for another tree.  Sterilize first if you need to re-use it.

Red Spider Mites.
      Appearance: Very tiny reddish insects mostly recognized by the presence of their very fine whitish hair-like webs, which sometimes form a loose ball around very small branches.  A piece of white paper placed under a plant suspected to have these insects should show some faint reddish powder when the plant’s foliage is shaken.
       Damage: They suck the plant juices.  Plants can be killed in a short period of time.
       How controlled: They are hard to kill but can be controlled.  They thrive in hot, dry, still surroundings.  The simplest approach is spray the foliage thoroughly with a garden hose or spray bottle.  Dusting sulfur can be applied when the temperature does not go over 90 F (hose the sulfur off after a day or so).  Special sprays can also be purchased, but hose washing or sulfuring the foliage is simpler and quite effective.
       Most susceptible plants: junipers (very susceptible, often turning grayish when badly infested), myrtle, sage, olive, citrus, and creosote (not noticeably damaged).

Scale, Hard.
      Appearance: Small (perhaps 1/8 to 1/4" elliptical or circular) hard waxy-shelled insects, often appearing on stems, branches and attached to the center vein of leaves.  A bad infestation appears as bumps on the bark.
       Damage: They suck the plant juices.  Plants can be killed in extreme cases.
       How controlled: A dormant oil spray applied in winter is said to be effective.  These insects can be gently scraped off with a thumb nail or sharp metal instrument.  Sometimes applying rubbing alcohol with a Q-Tip ® or cotton ball to the insect will work.
       Most susceptible plants: Olive and elm.

Scale, Soft.
      Appearance: Small soft gray-brown shelled insects, often appearing in crevices in the bark and at the base of branches or leaf stems.
       Damage: They suck the plant juices.  Plants can be killed in extreme cases.
       How controlled: Gently scrape off with a round toothpick or sharp metal instrument.  Sometimes applying rubbing alcohol with a Q-Tip ® or cotton ball to the insect will work.  Ants can spread the young scale insects, so eliminating ants (with diazinon) will help.
       Most susceptible plants: Elm and zelkova.

Whiteflies.
      Appearance: Tiny white flying insects in late summer, though most problematic are their immature nymphs.
       Damage: Mostly a nuisance, they suck the plant juices.  Can kill lantanas and other tender varieties in extreme cases, afflicted plants turning yellow and then wilting.
       How controlled: Spray foliage top and bottom with a soap solution every 3-4 days to break the egg hatching cycle.  Make up the solution with 1 tablespoon liquid dish detergent to 1 gallon of water.
       Most susceptible plants: Lantana, bougainvillea, gardenia, cherry, myrtle, sage, zelkova, elm, mesquite, acacia, and citrus.

Verticilium Wilt.
      Damage: A fungus that invades and plugs the water-conducting tissues in the roots and stems of plants so that leaves yellow at the edges, turn brown, and die.  Dieback progresses upward or outward from the base of the plant or branch.  Branches and entire plants die.
       How controlled: The fungus, which can survive in the soil for years, is favored by cool, moist soil.  There might be a chemical available that fights this usually fatal infestation. Sterilizing the soil in a black plastic bag placed in a sunny spot for several weeks in the summer seems to prevent outbreaks.  Maintaining vigorous health with proper fertilizing and well-draining soil helps minimize the damage.
       Most susceptible plants: Olive.

Root rot.
      Damage: This fungus destroys roots and is encouraged by overwatering and/or soil that does not drain freely.
       How controlled: Bare root the affected tree, cut off all infected roots, repot in fresh coarse soil mix in a sterilized pot.  Then dissolve Bordeaux mix in water and soak the soil with the solution.
       Most susceptible plants: Elm, juniper, and many others.
 

         Leaves, branches or entire trees which are affected and cut off should be tied up in a plastic bag and discarded.
 

A WORD OF CAUTION:  Do not use pesticides which contain either piperonyl butoxide or proper piperonyl.  These ingrediants are known to cause rapid leaf drop in elms, which is then only very slowly followed by bud regeneration.  The product Concern ® is a good and safe insecticidal soap.
 

       Earwigs, earthworms, and isopods (also known as roly-polies or potato bugs) can be physically removed from the soil if and when they are seen.

        Wound-seal is usually not needed, except for the largest pruned branches (2"+ in diameter).  A better method would be to just keep that area dry and clean.  Do NOT wound-seal conifers (they make their own perfect sealant).

        Learn something from each tree that dies in your care: learn so that another doesn’t have to go that way.  What does each tree need in order for it to be happy, healthy and alive?

        The two most widely used shapes are oval and rectangular.  Clay pots are a little more porous and able to breathe than glazed.  Glazed are more for deciduous and flowering trees.

        In the pot is the Soil, which provides

• Support, to hold up the tree;
• Nutrients (known and unknown), for the health and growth of the tree;
• Moisture retention, for electrolytes and nutrient solution for the tree;
• Drainage and evaporation, to help eliminate excess moisture;
• Aeration, for dissolved gas exchange by the roots -- aeration, NOT air spaces;
• Insulation, to moderate the temperature fluctuations of the container.

    Two basic soil mixes for the Phoenix area

    ½ decomposed granite (1/4 minus) or chicken / poultry grit + ½ general purpose potting soil mix.
        For conifers, use more granite.
 

    Four parts chicken grit + four parts forest mulch + one part peat moss.  For acid-loving plants, switch the last two ingredients to one part mulch + four parts peat moss.
 

>    "Cactus mix" might be too fine; pure perlite or even crushed pumice is better.  Orchid bark is a recommended source for organic material in a mix.  Less organic material in the mix is better here (down to even only 5 - 10%).  You DO have to relearn to water with that low percentage of organic material -- you'll probably be watering your healthy trees more often.  (Added 07/05/04)

        See also about soils.    (Added 10/29/05)

         Use at least a handful of the original soil mix in the new pot so as to inoculate the new soil with microorganisms the tree is used to.

        Roots, in bonsai:

• Tap, not needed for support (its primary function anyway), on a bonsai it causes the tree to sit up too high in the container;
• Surface, desirable for character: adds feeling of age and stability, provides visual balance;
• Fibrous, absolutely required for healthy tree: primary means of nutrient, water and gas absorption.

        Know your tree: on one extreme are the plants that cannot tolerate any root cutting; on the other extreme are young, vigorous plants like elms which can be bare-rooted.  Best not to wash all the soil off any plant.
        Examine the root ball: cut off encircling and strangling roots, roots coming out of the bottom drainage holes, or roots now extending beyond the sides of the pot.  A plant with this kind of root system is very healthy, possibly too vigorously growing.  Consider a little less granite in the soil mix, less fertilizer, less water, or a smaller pot.
        If there is very little new root growth since last repotting, do not cut off any roots now, but do increase the granite in the soil mix, increase the potassium fertilizer, or give the tree a season or two in a larger pot or growing bed.

        Position the tree off center in the pot.  Consider the best side/front of the tree, direction of surface roots, branch movement, any imperfections on the outside of the pot.
        Work the new soil mix in between the roots with fingers and chopsticks to remove air spaces.  If the container is plastic, you can strike the sides with the palm of your hand and tap the container on the ground in addition to using the chopsticks.  Take your time and work “all” the air spaces out.

        Mist the surface soil to start to break down the surface tension of the soil particles.  A top dressing of decomposed granite or chicken grit cuts down on water evaporation from the soil and makes it easier to water without washing soil away.
        Water thoroughly from the top to rinse fine dust particles out the bottom and to thoroughly saturate all the soil grains.

        Generally it takes one to two weeks after repotting for new fibrous root growth to become established, longer if air temperatures are below 70 F.