Greenhouse & NurseryDrainage Solutions

Greenhouse drainage is exposed to fertilizers, pH adjusters, and nutrient solutions that can be highly acidic or alkaline. Recommended materials include: (1) HDPE/polypropylene (NDS Pro Series, Dura Slope)—excellent chemical resistance across pH ranges; (2) Polymer concrete (ACO KlassikDrain)—good resistance with proper sealing; (3) Stainless steel 316 grade—best for hydroponic systems with aggressive nutrients; (4) Fiberglass reinforced polyester. Avoid galvanized steel, standard concrete, and cast iron which degrade rapidly in fertilizer-rich environments.

Nutrient capture and recycling requires proper drainage design: (1) Slope greenhouse floors or benches toward collection drains at 1-2%; (2) Install trench drains or floor drains at low points; (3) Route collected water to holding tanks through filtered systems; (4) Use sediment traps to remove growing media and debris; (5) Test and adjust nutrient levels before recirculating. Closed-loop systems can recover 20-40% of applied nutrients while reducing environmental impact. Ensure systems meet state agricultural discharge regulations.

Greenhouse floor slopes depend on the flooring type: (1) Concrete floors: 1/8" to 1/4" per foot (1-2%) toward drains; (2) Gravel or aggregate floors: 1-2% with subsurface drainage tile; (3) Fabric/membrane floors: 1-2% with underlying drainage layer. For bench systems, slope benches 1% toward collection gutters. Avoid flat areas where water pools—standing water promotes root disease, algae growth, and slipping hazards. Pre-sloped channel systems like NDS Dura Slope simplify installation.

Algae thrives in greenhouse drains due to moisture, warmth, and nutrients. Prevention strategies include: (1) Ensure complete drainage with no standing water; (2) Use opaque drain covers that block light; (3) Flush drains regularly with hydrogen peroxide or approved algaecides; (4) Install UV sterilizers on recirculating systems; (5) Choose smooth-surface drain materials that resist biofilm. Some growers add beneficial bacteria to outcompete algae. Regular cleaning is essential regardless of prevention methods.

Hydroponic systems require drainage that handles nutrient solutions and maintains sterility: (1) Stainless steel channels and floor drains for NFT and flood tables; (2) HDPE trench drains for Dutch bucket and bag culture systems; (3) Gutter systems with proper slope for ebb-and-flow benches; (4) Holding tank connections with filtration and treatment. All components must resist the specific nutrient formulation being used. pH levels in hydroponic solutions (typically 5.5-6.5) are mildly acidic—material selection should account for continuous exposure.

Subsurface drainage with perforated pipe is common under gravel or aggregate greenhouse floors: (1) Install 4" perforated drain tile in gravel trenches at 10-15 foot spacing; (2) Wrap pipe in filter fabric to prevent clogging; (3) Slope pipes 0.5-1% toward collection points; (4) Cover with washed gravel and landscape fabric before floor material; (5) Connect to daylight outlets or collection tanks. This approach works well for pot-in-pot nurseries and cut flower production where floor drains would interfere with operations.

Greenhouse drain sizing depends on irrigation method and peak flow: (1) Calculate total irrigation volume applied per zone; (2) Estimate runoff percentage (typically 10-30% of applied water); (3) Size drains to handle peak runoff in 5-10 minutes; (4) Add capacity for periodic heavy flushing. Example: A 10,000 sq ft greenhouse applying 0.5" of water has 3,120 gallons of irrigation; 20% runoff is 624 gallons. If drained over 10 minutes, you need 62 GPM capacity. Include safety factor for heavy watering days.

Greenhouse drainage regulations vary by state and municipality but commonly include: (1) NPDES permits for discharge to surface waters; (2) Nutrient management plans for runoff containing fertilizers; (3) Pesticide application restrictions near drainage; (4) Groundwater protection requirements in some areas; (5) Local stormwater permits. Many states exempt small greenhouses but regulate commercial operations. Best practice is to capture and recycle irrigation runoff rather than discharge. Consult your state agricultural agency and local planning department.