Urban Orchards : Plant selection

Contents:
A Brief Guide to Site Analysis and Plant Selection
Soil – What is it?
Preparing Soil for Planting

A Brief Guide to Site Analysis and Plant Selection

It is important to thoroughly evaluate a site and choose the plant(s) most appropriate to the site. Choosing a plant and trying to adjust the site to the needs of the plant involves a lot more work and is usually not successful. This is especially true regarding soil pH. Acid-loving plants planted in alkaline soil (such as soil near a concrete foundation or sidewalk - most urban soils) are doomed to failure. A plant under the wrong conditions is stressed and more vulnerable to attack by pests and disease. It grows more slowly and heals more slowly when injured. An orchard plant under the right conditions grows vigorously, actually wards off attack by pests and disease, and yields quantities of high-quality fruit each year.

Before beginning, have an idea of what you want regarding:
Fruit type: soft fruit (apples, peaches, berries) or nuts Plant type: dwarf tree, full-sized tree, shrub, vine, bramble Amount of labor you are willing to put into site preparation/adjustment

Plant Selection (see charts on plant selection):

Question: What are the plant's needs?

Sun required for good harvest: most fruit bearing plants require full sun; native understory (forest) plants tolerate partial shade (hazelnuts, currants, and juneberries) Drainage, pH, and fertility requirements:

Most fruit trees require good drainage, average pH, and moderate fertility.
Peaches, cherries, and grapes tolerate heavy, poor soil, dry conditions (sand).
Pears & plums tolerate poor drainage (clay).
Raspberries, kiwis, & blueberries require rich soil (high % organic matter, high fertility), with blueberries also requiring acidic soil (pH 4.5-5.5).

Site Analysis:
Question: What are the site characteristics?
Sun
Full sun: 12-6 hours per day. Partial shade: 3-6 hours per day (See hints below under “buildings...”).

Soil
Have soil tested for texture (including % organic matter), pH, fertility (N, P, K, and micronutrients), and metals (lead) and other toxics. Urban soils tend to be sandy, full of rubble, alkaline, (pH 7.0-8.0), low in organic matter, and of moderate to low fertility - because most urban land has been built on several times (with the exception of long time parks and urban wilds).
Water – watering becomes the main chore in the peak of summer when water is needed most.
Regular watering throughout summer for life of plant (raspberries, some shrubs), or only during first 3-5 years after planting (larger trees). Regular watering during fruit development (grapes). Occasional watering during weeks of drought. No watering: drought tolerant.

Site Analysis Continued – Special Features:
Lateral/vertical space: Know the size of your site, and how much space your desired plants require.

Underground space: Roots need a lot of room to grow (see charts). Space may be limited due to clay, hardpan, bedrock near the surface, foundations, or pavement. If the soil contains clay, hardpan, or breakable rock, make holes through layer with pickaxe before planting to help roots get through.

Buildings/trees: These limit sun. Learn the sun's path in late spring/early summer (high), early spring/late summer/early Fall (medium) and determine shade pattern. Sun's position in late fall and winter (low) is not relevant, Remember when estimating the sun's path to “put the leaves back on the trees” in your mind. In Boston, or anywhere around latitude 43 degrees N, from May 21-July 21 the sun rises ENE, passes 70 degrees (¾ of the way up) above the South horizon and sets WNW. The September 23 and March 21 sun rises due E, passes 47 degrees (about halfway up) above the South horizon, and sets due West. For other latitudes, subtract your latitude from 90 degrees and add 23.5 degrees for June 21 and 0 for September 22 or March 21 (2 examples: 37 degrees N (San Francisco, Virginia/North Carolina border, etc.): 90-37=53, so the sun on June 21 is 76.5 degrees up. 19.5 degrees N (Big Island of Hawaii): 90-19.5=70.5, so the sun is 94 degrees above S or equivalently 86 degrees above N horizon on June 21).

Wall:
South facing: Warm, dry microclimate will extend the growing season for long-season plants (grapes), provides winter wind protection (peaches, apricots), but plants require extra water. North facing: Cold microclimate will retard bloom of early blooming plants, preventing damage from late frosts (apricots, kiwis).
Slope:
South facing: Generally good for orchard trees, but can cause problems with southwest injury (sunscald – uneven heating of the trunk during winter, which causes bark to split). Sunscald can occur in bright sun areas even if there is no freeze-thaw cycle, but is worst when the angle of the sun is low and when there are no leaves to shade the trunk. As a preventative measure, paint the trunk a light color (white is best) on E, S, and W sides in N hemisphere (you might as well just paint the whole trunk). North facing: Especially good as it delays early, frost-susceptible bloomers. Bad for plants requiring long ripening season, but reduces risk of sunscald.
Erosion: Control by planting plants with fibrous surface roots (raspberries, strawberries).
Valleys, low-lying areas: Frost pocket: air pools and freezes, damaging early blooming plants (apricots, kiwis): plant on hillside/hilltop where air circulates/drains well.
Street-side: Auto fumes, salt, soil compaction, dry conditions. Plant hardy plants (hazels, filazels, Juneberries, Northstar cherries).
Fence/narrow space: Plant vines (grapes, kiwis), dwarf trees, shrubs, or prune trees as “espalier.”
Community: Assess interests/needs, ability to care for plants.
School: Select plants that are easy to grow, conducive to study, thornless (although there may be a reason for children to learn how plants protect themselves), harvestable during school year.
Community garden: Select plants that complement garden design and gardeners' interests
Urban wild: Select native plants that are favored by wildlife and tolerant of neglect (drought tolerant varieties, raspberries, Juneberries, hazelnuts, rugosa rose).

Other tips:
Choose healthy plants, in good condition (root mass in proportion to canopy, not root-bound). Choose plants hardy to your zone (at least zone 6 for Boston, preferably zone 5 or 4 to better ensure survival) and specific climate conditions (humidity, heat, etc.). As an example Northern Pecan or Paw Paw can survive a zone 6 winter but needs a long summer with consistently hot nights and days to ripen so are marginal in Boston. It also needs humidity and is difficult to grow in drier areas such as California. Contact local native plant societies or arboreta for lists of local native edible and other plants. In the Northeastern U.S., raspberry, juneberry, hazelnut, American persimmon, Paw Paw, hickory and walnut are native, yet there are varieties of these which are not local or which are not found in many microclimates. Choose pest and disease resistant varieties (see our information on pests and beneficials and diseases). Know the size that your tree will reach at maturity: dwarf, semi-dwarf, or standard. Know its growth habit: upright or spreading canopy, bushy, climbing, vigorous, invasive. Know the amount of maintenance that your chosen plants will require: watering, fertilizing, mulching pruning, training (vine, espalier), staking, susceptibility to pests/disease, fall clean-up, winter protection. Know the pollination requirements of your plants: self-fruitful or requires pollinator (see our information on plant propagation). Know your plants' harvest time. Plan for fruit ripening successively over a long period (or during June, Sept-Nov for schoolyards). Consider ornamental value: buds, blossoms, fruit, bark texture/color, leaf shape/fall color, overall plant shape/growth habit. Choose plants that attract desired wildlife: all orchard plants attract bees (which eat pollen and nectar), cherries and berry plants attract birds, nut plants (and stone fruit) attract squirrels, various “weeds” and wildflowers attract “beneficial” insects that feed on orchard pests (see our information on pests and beneficials for details and charts).

For additional information on selecting healthy trees, consult this article from Urban Forests Magazine. It deals with issues that you are more likely encounter with purchasing larger trees, something that you should avoid when choosing fruit trees.

Soil - what is it?

Ideal soil: Most fruit trees grow best in loam.
Sandy loam: Good drainage, moderate fertility. 45% minerals (50-60% sand, up to 25% clay, remainder silt), 5% organic matter, 25% water, 25% air, pH 6.0 - 7.0, abundant soil organisms (microbes, earthworms). When moist, loam should hold together loosely when squeezed in the palm of your hand. Loam is commonly found in woodlands or old pastures after years of natural decay of organic matter.
Soil texture: The mix of mineral (sand. silt, clay) and organic particles; affects drainage, pH, fertility, and water holding capacity.: Sand: Coarse particles that do not stick together, drain rapidly (in dry conditions). Low fertility (few nutrient-holding sites).; Clay: Fine particles that stick together, creating seal which offers poor drainage (saturated soil, not enough air – plants drown). Low fertility (holds nutrients, but does not release them).; Silt: Intermediate between sand and clay offering moderate drainage and good fertility (because it consists of organic and mineral particulates).; Organic matter: Ideally composes 5-6% of soil. Decay adds nutrients to soil and holding sites (like a sponge) for water and nutrients, enabling gradual uptake by roots. Provides pore space for air and supports microbe and earthworm populations (they break down organic matter, releasing nutrients in usable form for plants).
Fertility: The presence of essential nutrients in usable (water soluble) form, measured in ppm (parts per million). Major nutrients: Nitrogen (N), phosphorous (P), potassium (K) (“NPK” value on bag of fertilizer), calcium (Ca), magnesium (Mg), sulfur (S). Micronutrients (trace elements): Boron (B), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn). pH: Indicates soil acidity-alkalinity, which affects the availability of soil nutrients and biological functioning (most life shuts down at very high or very low pH). A pH of less than 5.0 increases solubility of toxic heavy metals which kill soil microbes.: Acidic (sour): pH 4.0-6.0, low.; Average (mildly acidic): pH 6.0-7.0, ideal for most plants.; Basic/alkaline (sweet): pH 7.0-8.0, high.
Nutrient availability depends on soil pH. Each nutrient has a pH range in which it is optimally available (example: blueberries require acidic soil because they need iron, which is optimally available at pH 4.5 – 5.5).
Nutrient concentrations: high or low concentrations of some nutrients restrict availability of other nutrients.

Preparing Soil for Planting – Increasing soil fertility

Organic matter: Compost, aged manure (see chart 'Selecting Organic Fertilizers'; see article 'Organic Soil Amendments and Mulches'). Till into soil in late fall and mulch with 4-6” of dead leaves. Microbe and earthworm populations recover from tilling and spend winter decomposing organic matter.

Fertilizers:
Natural – Usually slow release (do not try to accellerate the process bt burning plants or leaching from soil). Nutrients are present in natural balance relative to each other. Examples: blood meal (N), rock phosphate (P), greensand (K).
Chemical – Problems:
Contains nutrients in highly soluble form, causing them to leach from soil too quickly for plants to absorb. Acidifies soil, thereby killing soil microbes. Contains no organic matter, and therefore do nothing to build the soil.
Foliar fertilizing – Usually too much nitrogen for trees, which produces too much vigor. Liquid seaweed, nettle tea and other naturally derived sprays may be okay.

Correcting pH:
To lower pH by one point (make soil more acid), use 1 lb elemental sulfur (the type used in animal feed) per 100 sq. ft. (a 10 by 10 foot area). To raise pH by one point (make soil more alkaline), use 3-10 lbs ground limestone per 100 sq. ft. (depends on details such as “buffer pH”). This is rarely a need in alkaline urban soils.

Cover Crops and Green Manure Plants:
Dynamic accumulators are plants (weeds, grasses, legumes) that either...
...accumulate Nitrogen ftom the air into soils deficient in Nitrogen, or... ...accumulate a specific nutrient found somewhere in the soil (sometimes 'mining' the nutrient-sending roots down to layers rich in the specific nutrient).
Cover crop: A dynamic accumulator that is allowed to grow and accumulate nutrients indefinitely.
Green manure plant: A dynamic accumulator that is allowed to grow for a time, then tilled into the soil.

Cover crops and green manure plants improve soil by:
Increasing % organic matter by facilitating the decay of plant material.<.li> Increasing soil nutrients, making them more available to other plants (example: legumes 'fix' nitrogen). Minimizing leaching of soil nutrients – root hairs hold nutrients in soil. Improving soil structure – roots penetrate the soil, then die, leaving pore spaces for air, water, and microbes/earthworms. Moderating soil moisture, temperature - promotes root growth, keeps microbe populations healthy and active. Reducing soil pests – their dense growth chokes out unwanted weeds. Attracting beneficial insects – many cover crops/green manure plants are insectary plants (see article 'Attracting Good Bugs'). Sow in spring or summer of the year prior to planting, then till green manure plants into soil in late fall and mulch with 4-6” of dead leaves.