It is perhaps on the most sweltering days of summer that the cooling shade of trees is most appreciated- or missed. If your thoughts are turning to what to plant for future summer shade, here are a few ideas. On larger properties where space is ample, don’t overlook the potential for Big Leaf Maple, (Acer macrophyllum) (#M315), a Pacific Northwest native, to develop into classic shade tree dimensions. Where space is more limited, Vine Maple (Acer circinatum) (#M300), another Pacific Northwest native, can be trained to a single trunk for a moderate sized shade tree. Vine Maple is our primary native source of fall red and orange color.
Are you in a hurry to get your shade? The Empress Tree (#M580) is one of the fastest growing shade trees available to growers in mild winter areas, growing quickly to 20’, then more slowly up to 40’ tall. Tree serviceberries, maples, black locust (particularly Frisia), birch, and nut trees are all beautiful shade trees, and some produce food for you as well. Take a good look at your property, and choose a shade tree that will not overgrow your space. Locate your tree where leaves and other falling debris will not be a nuisance in your gutter, or on your sidewalk. You can also create shade by putting up a sturdy structure and training a vine over it, such as grapes, kiwi, akebia, or honeysuckle – a useful technique where root zone space is limited.
First we have to determine why. Sometimes it is in the nature of the plant not to grow vigorously in the first year, such as Monkey Puzzle or Bamboo. More often the root system is not growing and establishing properly. There can be several reasons why:
Perhaps the top of the tree started growing before the roots after the tree was planted (this often occurs when daytime temperatures are warm and the soil is still wet and cold after planting), creating an imbalance in the tree. The demands by the top of the tree for water and nutrients are using up all of the energy resources in the tree, so the roots aren’t growing. Re-establish balance in the plant by providing 50% shade from the mid-day sun, and keep the soil evenly moist (not constantly saturated).
Over watering a newly planted tree will keep the soil wet and cold. Check the soil 4-6” deep for moisture content before watering, where the roots are, rather than looking at the surface. In addition, if the ground remains constantly wet oxygen is pushed out of the soil, which the roots also need for active growth.
Too much modification of the soil in the planting hole can also lead to problems for the root system. Sometimes water does not exit the planting hole as fast as we thought it would, keeping the soil wet and cold, because the soil porosity created in the planting hole is too different from the native soil. Maybe the roots are not eager to leave the planting hole because what is in the planting hole is too nice compared to the native soil. Over-fertilization with chemical fertilizers or animal manures in the planting hole can burn the roots, stopping them from growing until the excess nutrients have leached out of the soil.
The best solution when preparing the planting hole? Keep the fertilizer to a minimum, do not add more than 20% compost to a planting hole (about 2 shovels full), and fracture the sides of the hole before planting. After planting fracture the ground next to the planting hole (I use a digging fork), mulch with straw or leaves, and water only as necessary the first few weeks. Finally, order your plants now through the first of the year so we can deliver them to you at the beginning of your planting season.
If the roots are not growing vigorously the top of the plant will not grow vigorously.
Spider mites thrive in the hot, dry weather of August. Inspect potted citrus, growing inside or outside, for spider mite infestation. Look for a yellow stippling pattern on the top side of the leaf, the under side will have light webbing and you may be able to see the small spider like insects moving about in the webbing. Willows, akebia, and himalayan honeysuckle are also favored hosts.
Control with insecticidal soap spray, applied every 3 days, for a total of three sprays. Then spray once a week until the hot dry weather is done for the year. You may add a light weight oil, such as canola or neem oil, to improve the effectiveness of your spray. Use 1-2 Tbsp of oil per gallon of spray solution, or follow the label if you choose an ultra-light summer weight oil. If you add oil, do not spray when temperatures will exceed 80° F or you may see leaf damage. Always test a new mixture on a few leaves first, to make sure you won’t damage leaves. Some plants are very sensitive to oils. Our Raintree Plant Owners Manual has more information on controlling insects on your potted plants, see page 16.
Fertilize container plants as needed to maintain adequate fertility for healthy growth. Summer watering can flush nutrients out of the soil mix. Slow release fertilizers may not be contributing much nutrient any more. Use a liquid fertilizer to finish out the growing season, or another light application of slow release. A formulation with less N (nitrogen) and more P (phosphorous) amd K (potassium) will help plants finish ripening fruit and prepare for winter with more sturdy growth.
During the long hot days of summer irrigate as needed to provide the equivalent of 1” of rain per week (enough water to saturate the soil to 1 foot deep). Irrigation is especially valuable for newly planted trees (1-2 years) whose root systems are not fully established deep into the soil. Mature fruiting trees will also benefit from irrigation in the last few weeks before the fruits are ready to pick. Water in the tree is used to fill and expand the cells in the fruit. Extra water will pump up the fruit so it is large and juicy when you pick. During extreme heat episodes, a little more water than you are accustomed to applying may be needed to reduce signs of heat stress in your trees such as excess early fruit drop, leaf wilt and leaf curl. It is important to provide the water to the portion of the root system that will take it up. Apply the water to saturate the soil from just inside the leaf canopy to several feet beyond the drip line. Avoid wetting the foliage and fruit of fruit trees that are sensitive to brown rot, powdery mildew, and other fungal diseases. Drip irrigation allows you to use less water, keep the foliage dry, and still accomplish the goal of maintaining your trees.
As plants start heading into dormancy later in the month, or early September, you can begin to water less frequently, but don’t let plants get too dry. Plants whose inner or lower leaves turn yellow and drop are likely showing a drought stress response, as oldest leaves are shed when water supply becomes short. If drought becomes severe, early fall color and total leaf drop can occur. A word of caution: These very same symptoms can show up when excess water in the planting hole drowns roots (displaces oxygen from the soil). This can even occur in a well-drained soil, if the soil in the planting hole was significantly modified at planting time. Dig below the surface. If you find waterlogged soil that smells bad, you probably need to correct soil drainage or your watering practices.
VINES: Manage the canopy of your vigorous grape vines. As fall approaches it may be desirable to remove some leaves, or shoots, to expose ripening fruit to the sun. Vines can be cut off at the fifth leaf past the last fruit cluster to improve air circulation and sun exposure. Your kiwi vines may also be growing out of control. Cut back any vigorous shoots that are growing over the top of your selected producing side shoots to the point of origin if they are not needed, or to the width of your trellis if you need them to replace or fill in as a fruiting arm. See Growing Kiwifruit (#S240 ) for more information on managing and caring for your kiwi vines.
ESPALIER: Cut back the pinched-out shoots on fan-trained plums (until mid-September). Cut out old fruiting laterals on established fan-trained acid cherries, peaches and nectarines as well after they are done fruiting. Continue maintenance pruning of established pear and apple espalier trees. In the Pacific Northwest the modified Lorette pruning system recommended in the RHS Fruit book may induce late summer bud break lower in the shoot than is preferred, reducing the number of flower buds for next spring. Instead, through August keep vigorous upright shoots controlled by cutting them back to a point about 6“ above where you want fruit buds to initiate. The top buds you leave will grow, with less vigor than the shoot you removed, well above the initiating flower buds you prefer to stay dormant. Next winter cut those vigorous shoots back to the flower buds that have initiated at their base to develop a new fruit spur. The book Pruning and Training-Revised by Brickell and Joyce, (#S325) has excellent line drawings and instructions to help you train and maintain your espaliered fruit tree.
NUTS: Break (brut) vigorous lateral shoots on filberts to about ½ their length and leave them hanging, to help improve air circulation in the tree and ripen next year’s new fruit buds. Thin those same shoots in winter to 3-4 buds. Thin out long thin crowding shoots on established sweet chestnuts and walnuts.
BERRIES: Remove fruiting canes of raspberries and blackberries after all of the fruit has been picked, but leave this year’s new canes to produce fruit next year. If you left the lower portion of your primocane berries last fall then finish removing them this month after you have picked all the fruit they produced, leaving this years’ new canes to produce later this month and into September. Pinch out runners on day-neutral strawberries to focus their energy on continued fruit production. Late July or early August mow over the top of your main season strawberry beds (mower set at highest position) to clean up old leaves and encourage new leaf growth. Remove runners that are crowding the bed, or re-position to a spot in the bed that needs filling in.
FRUIT TREES: Try to finish any summer pruning you have left to do before the latter part of the month, focusing more on thinning cuts. Any new growth that occurs late in August, or later, will tend not to harden off properly before winter settles in, and will then be more susceptible to winter damage.