Once your trees are planted, here's how to keep them growing strong and producing an abundant harvest.
During the first two growing seasons, water the trees deeply (6 to 8 gallons of water per tree) about once a week if there's been little or no rain. Don't apply less water more frequently. That will encourage shallow rooting.
Irrigate bearing fruit trees if they receive less than 2 inches of rain during any 2-week period between bloom and early fall. If no rain has fallen for 2 weeks, this means you need to add 1 gallon of water per square foot of rooting area, which extends several feet farther out than the tree's dripline. Measure rain and sprinkling systems with open containers on the ground. The most critical time to water is during fruit expansion, but don't apply more than 2 inches. Excessive watering can cause fruit to expand too much and be more prone to rot.
Spread 4 to 6 inches of mulch around the trees to their dripline to conserve moisture and control weeds. You can use bark mulch or other attractive mulches and plant noncompetitive flowers (spring bulbs and shallow-rooted annuals) around the trees. Before spreading straw mulch, let it sit out and wet it several times to encourage weed seed germination.
You can grow a lawn or other groundcover between the mulched areas around the trees, and the mowings can be used for mulch. You might plant quick-growing annual cover crops such as buckwheat and annual rye during the first few years to provide organic matter, but as the trees get older, you'll need to establish a permanent groundcover. Legumes such as bird's-foot trefoil (with yellow flowers) or crimson clover (with red flowers) make attractive groundcovers where they are adapted. Mow grasses to reduce competition, and mow legumes frequently to reduce stinkbug injury. Groundcovers that don't require mowing include wildflowers and noncompetitive evergreens such as vinca minor and creeping phlox. Avoid warm-season grasses such as Bermuda or zoysia, and competitive groundcovers such as pachysandra. Ask your nursery for other recommendations for your area.
Supply fertilizer and abundant organic matter during the first few years to get the trees off to a good start, but keep in mind that heavy or careless applications of fertilizer can damage the trees. To avoid burning the new root system, wait 6 weeks after planting to fertilize. Then apply a fertilizer containing 1/10-pound of actual nitrogen in a wide band 1 foot out from the trunk. It's best to apply a nitrogen source separately and adjust phosphorus and potassium according to soil test results, although a complete fertilizer can also be used. You can apply nitrogen in any form as long as it equals the specified amount. Don't plan on supplying all of a young tree's nitrogen needs with compost or manure. If you added enough to do that, nitrogen would still be released in early fall, inducing the tree to grow too late in the season and predisposing it to winter injury. During the summer, check the amount and color of growth to guide you in fertilizing next year. Leaves should be dark green and terminals--the shoot growth from the sides or end of a branch--should grow 16 to 20 inches during the season. If trees received adequate water but leaves are yellowish and terminals didn't grow that long, add more fertilizer next year. If terminals grow 22 inches or more, cut down on fertilizer.
During the second growing season, make two fertilizer applications: one when growth begins in spring and one in early summer. Apply about 1/8-pound of actual nitrogen each time, if growth was in the desired range last year.
Established fruit trees require little fertilizer other than organic matter. From the third season on, apply only enough nitrogen to produce the desired amount of growth. Bearing trees that produce crops on 1-year-old branches (peaches, apricots, and Japanese plums) should make 15 to 18 inches of terminal growth per season. Those trees which bear mainly on spurs (apples, pears, cherries, and European plums) should make no more than 10 to 14 inches of terminal growth per season.
Excess nitrogen can cause poor fruit bud set, poor fruit color, delayed fruit maturity, and softer fruit, which is more prone to rot and doesn't store well. Time fertilizer applications so that nitrogen will be released when growth is starting in spring, and when fruit buds are forming in early to midsummer. Established trees usually don't benefit from phosphorus applications in most soils, and excess phosphorus can cause zinc deficiency. Potassium may be deficient on alkaline soils high in calcium and magnesium. Potassium deficiency reduces fruit size, sugar content, and storage time; it can be recognized by small, bluish-green leaves with yellowed or dying edges. Zinc and boron must be applied frequently on western, alkaline soils. These are best applied as foliar sprays; ask your county Extension Service agent for details. You can apply liquid seaweed emulsion throughout the growing season to provide small amounts of trace elements and cytokinins, growth hormones that reduce stress on the tree. Foliar nutrient sprays can be added to pesticide sprays.
Each fall, fruit trees begin to harden up in preparation for winter. Growth slows and metabolic changes take place that enable plants to withstand much lower temperatures without damage. Help the plants harden by allowing their growth to slow. Don't apply too much fertilizer or apply it past midsummer because high nitrogen levels will cause continued growth. Don't water from early fall on, except when less than 1 inch of rain has fallen during a 2-week period. Mow around the fruit trees less often in early fall to allow the lawn or groundcover to compete and help slow tree growth. Do not prune in fall, so as not to stimulate growth or leave fresh cuts open to winter injury.
During the winter, desiccation can cause as much injury to plants as cold temperatures. Water trees well in late fall (not early), after they are dormant, but before the ground freezes, if the weather has been dry. Rake fallen leaves. Compost them only if you're sure they are disease-free.
Paint tree trunks white in late fall to prevent winter sunscald. This damage, often worse than that from absolute cold, occurs when the unshaded trunks heat up to high temperatures during the day, then rapidly cool to very low temperatures at night. Combine 1 part interior white latex paint to 3 parts water, and spray or brush this mixture on trunks up to the first main limb.
Rabbit and rodent repellents can be mixed into the paint to prevent these animals from feeding on the bark in the winter. Or place 1/4-inch mesh hardware-cloth cages around your trees, making sure the guards reach above the expected snow level. You can also use white plastic tree guards to prevent both sunscald and rodent damage. Pull mulch away from the tree trunks in fall to avoid attracting rodents. Deer feeding on the tender twigs and branches in winter can cause a lot of damage. The most effective deer repellent, according to those troubled by them, is an egg spray. Blend three raw eggs with two or three cups of water in a blender, then dilute this mixture with more water in a 3-gallon sprayer.