Objectives : Provide enough space between plants and potential sources of contamination to minimize the risk of contamination via water splash.
What you need to know: The ground surface, even if it is covered with gravel or landscape fabric, is nearly impossible to maintain as a clean surface. The common practice of placing containers on or near the ground is generally not compatible with clean production.
Best practices:
6.3.1. Keep all plants on benches that provide at least 0.76 m (2.5 ft) of distance between the bottom of plant pots and the underlying surface to minimize the risk of contamination via water splash. Increasing the minimum height to 0.9 m (3 ft) provides a greater margin of safety (see rule of thumb 6).
6.3.2. Bench tops should be made of expanded wire mesh or other open, nonporous materials that do not allow water to move between pots and can be effectively sanitized. Plywood, wood pallets, or similar solid surfaces that allow water to pool or run laterally are not acceptable. Do not use benches that have wide horizontal surfaces that can catch and hold water or debris.
6.3.3. Wood is difficult to keep clean and to sanitize, so its use in nursery benches is generally discouraged. Wood is acceptable in applications such as upright members (bench legs) or other supports that do not catch soil, water, plant debris, etc.
6.3.4. Manage surfaces underneath benches, in walkways, driveways, and elsewhere in the clean area to prevent puddles, eliminate potential for splash, and remain free of weedy vegetation. Maintain adequate drainage and use gravel, landscape fabric, pavers, concrete, or other materials to keep underlying soil covered and avoid having exposed wet soil or mud.
6.3.5. Allow as much horizontal space as possible between benches and between blocks of plants within benches to minimize the potential for cross contamination via splash. Where it is not practical to provide a relatively safe gap of about 1 to 1.5 m (3.2 to 5 ft), barriers made of plastic film, acrylic sheets, etc., canbe used to prevent cross-contamination via water splash between adjacent blocks on a bench. Note that if contamination is detected, all plants within splash distance of a Phytophthora-infected plant or block of plants need to be quarantined for further testing or discarded, so maintaining separation helps localize spot infestations to the fewest plants possible.
6.3.6. Increase spacing between containers within blocks where possible to reduce the potential for splash contamination between containers.
3/8/2021-Minor edits