Consider soil drainage prior to field planting

Field grown nursery crops are perennials that remain in the ground for 3-5 years. Over this time span the goal of a nursery manager is to ensure that the stock is given the best environment as possible to ensure efficient plant growth. Whether the field stock consists of ornamental shade trees, shrubs, herbaceous perennials, Christmas trees, bulbs, or lawn turf, the best production comes with site selection and development. Pre-plant site preparation is as important as post-plant cultural management. By not preparing a piece of ground properly, managers will generally be disappointed with challenges that come with growing their stock.

Selecting the best ground
Once a nursery plot map has been developed, the portions of the acreage that will be devoted to planting beds (often referred to as blocks) should be walked and marked out with wooden stakes and flagging ribbon. Only the very best ground should be selected for planting with the remainder of the ground devoted to roads, structures, windbreaks, buffers along water courses, any other type of operation that does not involve actual stock production (1).

While it is possible to greatly improve poorer sites with organic matter additions, or drain tile installation for reducing water saturation during the winter, these supplemental development steps are expensive. It is often less expensive over the long run to simply lease or purchase better ground. Generally field beds will have less than 10% slope in order to ensure safe and efficient machinery travel as well as to reduce worker exertion that comes with steeper ground. Rocky or stony ground should be avoided as it makes tillage and digging more difficult.

Land drainage systems
The Pacific Northwest is know for mild winters and prolonged periods of winter rains. On certain soil types water will on the soil surface after extended periods of rainfall. When the soil becomes saturated the nursery manager is faced with a number of difficult challenges in raising and harvesting field stock. First off, plant growth will be reduced. In well drained soil plants will be able to extend their roots deep into the soil profile. However in poorly drained soils root systems will be tend to become shallow (2) and less well developed as the water table rises during the winter. With smaller root systems, perennials will be more susceptible to summer drought stress, and will lack the ability to take up essential nutritional elements. Erosion is often a problem on poorly drained sites as the surface water will move laterally. Water logged soils also encourage the growth of soil pathogens such as Phytophthora spp. (frequently Phytophthora cinnamomi) in a wide range of ornamentals in both field and container nurseries (3). A common cultural suggestion (4) to avoid damage by soil pathogens, including Phytophthora spp., is to plant nursery crops on well drained ground.

Subsurface drain tile
In order to keep the water table below the rooting depth in the winter, subsurface drain lines can be installed prior to planting a field (5). Figure 1. depicts tile arrangement.

In the Northwest, PVC drain tile lines are typically set a depth of from 30"-40". Spacing between tile lines can range from 20' to 80' (6) with the closer spacing applicable for poorly draining ground. If tile lines are installed by an experienced contractor, the resultant water will remain at or slightly above the depth of the tile line, thus effectively keeping the roots of the plants above from being inundated. Tillage operations will become considerably easier, especially during the winter and harvesting season as machinery won't be mired in soft ground. Bare root stock will be easier to dig up as there won't be as much wet soil to cling to the root systems. A drier soil will also warm up faster in the spring thus encouraging earlier plant growth.

Installing drain tile prior to establishing a shade structure

There are economic reports examining the costs and returns for the installation of subsurface drainage systems (7). It's not uncommon to find costs of installing 4" PVC drain tile (8) at a 3'-4' depth to be $1,200 per acre. However, the nominal costs of installing drain tile should be recouped in less than 2 years as the nursery manager will be able to utilize the site all winter.

Drain tile work has to be conducted during the drier months of the year. It's generally preferable to perform tile work on fields which are still in sod. A smoother, firmer surface is preferable (9) to roughly plowed or finely worked summer fallow field. Once installed the tile lines should not interfere with normal farming practices of plowing, and disking. If it has been installed at a 4' depth, tile lines should not impact digging woody ornamentals with anything but the largest mechanical tree spades (10). Nursery managers generally consult with an agricultural drainage contractor before considering tile installation. The specialized machinery and skilled labor needed to lay the tile preclude even the largest nurseries from performing the work themselves. Once installed the location of all the tile lines should be recorded (11), preferably with GPS coordinates. This final step will help reduce the chances of digging up the expensive tile lines inadvertently in the future.

Flood plains
It's important to know the boundaries of flood plains near the nursery site. While some of the most productive wholesale nurseries in the Pacific Northwest are located on flood plans, growers typically use their fields for bulbs, herbaceous perennials, and turf fields. It's still a gamble not to loose a crop when rivers overflow. The U.S. Geological Survey maintains an interactive web site (12) that shows the daily in-stream flows from rivers all across the United States. Even shot term flooding of 1-2 days can have disastrous effects on ornamental trees, shrubs, and Christmas trees. Only the most flood tolerant native shade and shrub trees will survive (13). The Oregon Association of Nurseries also maintains a listing of wetland and aquatic plant nurseries (14).

Runoff from either field grown or container stock can be diverted to the retention pond to help filter the water and make it suitable for using it again for irrigation.

References
1. Nursery Management Administration and Culture. 1994. Harold Davidson, Curtis Peterson, and Roy Mecklenburg. Prentice Hall Career and Technology, Englewood Cliffs, New Jersey. Distributed through the American Nurseryman Publishing Company.

2. Benefits of drainage. 1997. Vincent LaLonde and Geoff Hugh-Games. British Columbia Ministry of Agriculture, Fisheries, and Food. In: Chapter 6 of the B.C. Agricultural Drainage Manual.

3. Phytophthora root rot on woody ornamentals. 1996. Austin Hagan and Jackie Mullen, extension plant pathologists, Alabama Cooperative Extension, Auburn University.

4. Phytophthora root rot and its control on established woody ornamentals. 2000. D. Benson, and R.K. Jones, extension plant pathologists, North Carolina University.

5. Land drainage. 1984. D.E. Boyer. Chapter 13, Production of Bareroot Seedlings, in: U.S. Forest Service Forest Nursery Manual.

6. Understanding agricultural drainage. 1997. Larry Brown and Andrew Ward. Food, Agriculture and Biological Engineering, Ohio State University.

7. Economics of subsurface drainage. 1998. Janin Nyvall, drainage engineer, British Columbia Ministry of Agriculture and Food, Abbotsford, BC.

8. Advanced Drainage Systems, Inc., Hilliard, Ohio.

9. Management of drained fields. 1979. R.W. Irwin, Ontario Ministry of Agriculture and Food.

10. Optimal Tree Spades, distributed by Bennett and Bennett Enterprises, LLC, Gatlinburg, TN.

11. Maintenance of the drainage system. 1991. R. W. Irwin, Ontario Ministry of Agriculture and Food.

12. Water Watch: Current water resources condition. United States Geological Survey. Map of real-time stream-flow compared to historical streamflow for the day of the year. Data available for all 50 states.

13. Sound Native Plants. Olympia, Washington. A commercial nursery supplying both field grown and container nursery stock for flood prone sites.

14. 2003-2004 Directory and Buyers Guide, Oregon Association of Nurseries, Wilsonville, OR.

First posted: December, 2004.