Typical site arrangements. A, C - warm locations; B, G - top may be too cold in winter; D, F - susceptible to spring frosts; E - can still be frosty, but the woods act as a windbreak.
Site Selection and Soil Preparation
Shortcuts and haphazard approaches can result in less-than-ideal growth and other problems during the orchard's life. It is easier to amend a site before the trees are planted than it is once they are in the ground. Penn State has an excellent video on soil preparation that you may view on line.
To build a good orchard, you need a good foundation. The ideal site is on rolling or elevated land so that cold air can drain during spring frosts. Figure 1-1 shows typical site arrangements. Site A is a warm location that receives more sun. This site is not affected by late spring frosts because cold air drains to lower-lying areas. Site B also misses late spring frosts, but the top may be too cold in winter because of exposure. Site C is similar to site A but colder, warming up later in the spring. Site D is the most susceptible to spring frosts because cold air drains into it from elevated areas. Site E can still be frosty, but the woods act as a windbreak, sheltering this site from prevailing winds. Site F is not desirable because of the dense woods at the base of the hill. Woods can trap cold air and prevent it from draining to lower-lying areas. Site G is similar to site B.
Table 1-1. Number of trees per acrea at various tree spacings.
Slope exposure should be considered for its effect on fruit trees as they come out of dormancy. A southern-facing slope warms up faster in spring, while the opposite is true of a northern slope. Eastern-facing slopes are intermediate. In Mid-Atlantic areas, a western-facing slope tends to be windier. Wind can cause spraying problems during the growing season.
While uphill or rolling land is the most desirable, the degree of slope can also limit its suitability. The ideal site has a 4 to 8 percent slope. It may be difficult to operate machinery on slopes of more than 10 percent.
Selecting a site for an orchard involves below-ground considerations as well, primarily soil depth and soil texture. An old recommendation for a desirable orchard soil is that it be deep and well drained.
Soil drainage is probably the most important factor in the longevity of an orchard. This is because of the inherent inability of certain types of fruit trees to survive when planted in imperfectly drained soils. Stone fruits (peaches, cherries, and plums) are the most susceptible to poor drainage. Apples are intermediate, and pears can survive on the more poorly drained soils.
Soils are made up of four basic ingredients: mineral elements, pore space, organic matter, and other items consisting mainly of living organisms, including fungi, bacteria, and nematodes. One classification of soils is based on the mineral part of soil and consists of four sizes of particles. Clay particles are the smallest, followed by silt, sand, and gravel. The USDA has devised another system of classifying soil particles. In this system soil is divided into seven categories: clay, silt, and five sizes of sand.
Soil texture is determined by the percentage of sand, silt, and clay in the soil. Arendtsville gravelly loam, Highfield channery silt loam, and Steinsberg sandy loam are examples of soil types having different textures. The structure of a soil is influenced by soil texture and also by the aggregation of small soil particles into larger particles. The amount of aggregation in a soil is strongly influenced by the amount of organic matter present.
The pore spaces in a soil are normally filled with air or water. As the amount of water increases, the amount of air must therefore decrease. The pores of a well-drained soil have certain physical characteristics that, after a period of heavy rainfall, enable water to rapidly drain away and allow air to return to its original percentage.
The amount of organic matter in soil is an important factor in soil structure. Organic matter consists of dead and decomposing plant and animal parts. Living organisms break down plant debris into organic matter.
The cation exchange capacity, or the ability of soil to store cations (positively charged particles) is highly dependent on the amount of clay and organic matter in the soil. Clay and organic matter contain predominantly negatively charged sites that attract cations. Applied nutrients such as ammonium nitrogen, potassium, calcium, and magnesium attach themselves to the negatively charged soil particles. This phenomenon is called cation exchange, and it allows the soil to be a reservoir for plant nutrients.
Before selecting a site for an orchard, consult a county soil map. Soil surveys are available at most Natural Resources Conservation Service offices in Pennsylvania. These publications are valuable in determining if your particular site has the detailed requirements for a long-term viable orchard operation. In addition to hard copies of soil maps, growers can access detailed soil information online. You may access soil information specific to your site at the USDA NRCS Web Soil Survey. A more detailed site evaluation is probably warranted, and we recommend that a backhoe be used to dig holes 5 to 7 feet deep so that the soil profile can be examined. A test similar to a percolation test used for installing septic systems may also be advisable where internal soil drainage is questionable. Poorly drained soils often have horizontal layers of light-colored material.
Although pH and fertility are often considered important factors for orchard soils, internal soil drainage is actually the most important. Soil fertility can often be corrected by applying fertilizer or by increasing the level of organic matter in the soil. Soil pH can be corrected and is not usually a limiting factor unless a site is highly acid. In this case only the plow layer depth can be corrected with applications of lime.
The best soil is a well-drained loam a minimum of 3 to 4 feet deep. Good drainage, however, should take preference over depth. In Figure 1-1, soils at site B are most likely to be the shallowest because of erosion, while those at site D tend to be the richest. Soil fertility should be medium to low. Overly fertile soils can lead to excessive tree growth at the expense of fruit production. Adding fertilizer to increase tree vigor is easier than trying to reduce vigor. Fruit trees grow well in soil with a pH of 6.0 to 6.5. Higher or lower levels can cause nutrient deficiencies.
Once you have selected a site, you must prepare it. If you are replacing an existing orchard, particularly a stone fruit orchard, it is important to rotate into biofumigant cover crops for at least two years before planting a new orchard. The cover crops are also effective in correcting soil physical problems such as compaction, which can occur from equipment driving over the previous orchard. Take a nematode test before the old trees are removed to determine the need for fumigation. Nematode tests are recommended even when the site was not formerly an orchard since nematodes can severely stunt young trees or transmit viruses. For more information on nematode management, see Nematodes: The Unseen Enemy in Orchards. Next, take a soil test to determine soil fertility. Penn State provides a soil testing service through the Agricultural Analytical Services Laboratory for a fee. You can contact them by going to the lab’s website or calling 814-863-0841. Fertility and pH should be adjusted to optimum levels prior to planting a new orchard since lime and certain fertilizers move very slowly in soils. With some of the bitter-pit-prone cultivars, such as Honeycrisp and York Imperial, it is especially important to adjust pH to 6.5 prior to planting your trees. Private labs that can analyze your soil are also available. When starting a new orchard, you may want to consider also having the lab test the organic matter level in your soil. Organic matter is an important consideration in determining how vigorous or fertile your soil may be and also affects soil drainage. If you are replacing an existing orchard or clearing the land for a new one, take the soil sample after removing the trees and as many of the roots as possible. An initial plowing and leveling should also be done before taking the soil sample. In this way, any subsoil that comes to the surface can be thoroughly mixed.
A two-year crop rotation prior to planting will also aid in weed control. Examine the field for the presence of perennial weeds before working the ground. If multiflora rose, thistle, poison ivy, or hackberry are in the field, they should be treated in the summer or fall with glyphosate. If the problem weeds have been established for a number of years, controlling them will require two or three treatments of glyphosate. It is best to subsoil as deeply as possible. Running a deep shank in two directions across the field will break up any existing hardpans.
Chop and plow down cover crops in late summer to increase soil tilth and organic matter. Take another soil test before doing the final disking and leveling. Incorporate any needed amendments, such as lime, phosphorus, or potassium.
Orchard sod should be planted the fall before trees are planted. The grass cover traditionally used is Kentucky-31 tall fescue. It establishes itself rapidly and is a durable cover crop, although it does require frequent mowing during the growing season. The ideal time to plant seed is mid-August to late September. Seed the grass at a rate of 20 to 40 pounds per acre.
Replanting an Orchard Site
Replanting an old orchard block requires a specialized approach for preventing replant disorders and stunted tree growth. Soils often need to be rejuvenated over several years. Over the life of an older orchard the nutrients and soil pH decline and the old tree rows may have developed herbicide residues that will suppress young tree growth. Organic matter can decline as orchards age. These problems need to be remedied. The following steps are recommended to help prepare the site beginning the fall after the last harvest. Remove old trees and roots. Rip the soil thoroughly to expose additional roots and large rocks for removal.
- Collect samples for soil nutrient and nematode tests. Soil tests should include soil organic matter as well. Cornell University offers a soil health test that measures available water capacity, surface hardness, subsurface hardness, aggregate stability, active carbon level, phosphorus and potassium levels, minor elements, and textural class. They provide a color-coded numeric rating value for each of these parameters plus an overall score.
- If perennial weeds were present, treat the entire site with glyphosate to kill them.
- Apply lime to adjust soil pH to 6.5 and incorporate by deep plowing. If more than 1,500 pounds of lime are required, apply half before plowing and incorporate the remaining half after plowing by disking.
- Broadcast 50 pounds of actual nitrogen per acre along with required amounts of phosphorus and potassium needed for forage crops, based on the soil test results, and incorporate them into the soil.
- In early June plant Sudex (a sorghum x sudangrass hybrid variety of Sorghum bicolor) at 35 to 45 pounds of seed per acre. Sudex produces a large amount of biomass quickly and the roots will penetrate 4 to 6 feet deep. The addition of the organic matter should also help reduce herbicides residues from the previous crop.
- In mid-August, mow sudangrass using a flail mower or use another strategy to chop and macerate the grass as much as possible. Incorporate the residue immediately and follow with a cultipacker. It’s best not to mow down more area than can be plowed under within two hours.
- The soil conditions during sudangrass incorporation should be similar to those for soil fumigation (i.e., some soil moisture and soil temperatures above 50°F). Mowing injures the plants and initiates a process that releases nematicidal compounds into the soil.
- Incorporate 50 to 75 pounds of ammonium sulfate per acre during the disking of the sudangrass. The sulfur may acidify the soil, but it should increase the amount of toxic materials produced following the rapeseed crop.
At least two weeks after plowing down the Sudex residue plant ‘Dwarf Essex’ rapeseed at 8 to 10 pounds per acre. The ideal planting date for southeast Pennsylvania is September 15 and somewhat earlier for more northern areas. The goal is to have developed a rosette by winter so that it will overwinter well, but not too much vertical growth, which can winter kill. Rapeseed produces natural chemicals that are toxic to plant-parasitic nematodes.
- The following spring in mid- to late April mow the rapeseed with a flail mower and plow down the residue immediately. Soil conditions during rapeseed incorporation can affect the efficacy of the rapeseed. Soil temperatures should be above 50°F and moist. Never mow down more area than can be plowed under within two hours. Flail mowing injures the rapeseed and releases the nematicidal chemicals into the soil. Failure to incorporate mowed rapeseed quickly allows much of the nematicidal compounds to escape by volatilization.
- Two weeks after plowing down the first rapeseed crop, broad-cast 50 to 75 pounds of ammonium sulfate and plant a second crop of ‘Dwarf Essex’ rapeseed or a second crop of sorghum sudangrass. The two-week interval is important to prevent phytoxicity to the summer rotation crop.
- Collect and submit soil samples in early August for pH and basic fertility levels to obtain results by early September.
- In mid-August mow down and incorporate the cover crop as done previously. Broadcast any lime needed to adjust soil pH to 6.5 and other needed nutrients from the soil test report, along with 15 to 20 pounds of actual nitrogen per acre. Do not use ammonium sulfate. The lime and other nutrients, including the nitrogen, can be applied before mowing and incorporating the biofumigant crop, or after, depending on the height of cover crop and practicality.
- After leveling the soil, plant the chosen grass seed evenly across the acreage (see the Row Middle Management section).
- Two weeks prior to planting the new trees, apply a glyphosate herbicide product as a directed spray to kill the sod cover in
4-foot-wide strips marking the planting rows. Try to avoid using the old tree rows for the new trees, and leave the killed sod in place and plant trees through the sod with a tree planter.
Source: Penn State Tree Fruit Production Guide.