Mar 9, 2020
Water, weeds and spacing key to hoop house production

Water is necessary for plant growth but can bring on diseases. Crops need adequate space to grow but giving them too much space is inefficient and makes room for weeds. Tie it all together and water, weeds and spacing are the keys to hoop house production.

“It gets to be how they’re interacting and how they work as a system,” said Jeremy Moghtader, program manager of the University of Michigan U-M Campus Farm and a speaker at the recent Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, Michigan.

Moghtader is formerly the director of programs for the Michigan State University (MSU) Student Organic Farm, where he also served for 10 years as farm manager. In his time at MSU he developed and directed the MSU Organic Farmer Training Program and the Farmer Field School creating courses, teaching and giving talks on organic and ecologically based farming techniques.

The University of Michigan Campus Farm is GAP-certified (Good Agricultural Practices) and supplies the U-M Food Service with about $120,000 of fresh produce each year. The farm uses organic practices but isn’t certified organic and is part of U-M’s Matthaei Botanical Gardens.

The research and teaching facility has a nine-acre footprint, four acres of vegetable production, cover crops and research fields, and four 30-foot by 96-foot hoop houses.

Both drip and overhead irrigation are used. “Blights and many other diseases don’t establish without free water on the leaf surface and that’s why we use drip irrigation,” Moghtader said. Drip also allows fertigation when supplemental nutrition is needed in-season.

Overhead irrigation is used occasionally to fully moisten the soil profile and stimulate soil microbial activity. “The biological activity that drives nutrient availability in an organic system requires moisture,” Moghtader said.

Varied irrigation needs

The irrigation strategies vary with the crop.

For some crops, like kale and spinach, overhead irrigation is used to get the soil moisture up to the right level before planting to aid establishment. Drip irrigation is used later in the season for routine watering. Drip irrigation keeps the environment drier than overhead irrigation and reduces disease.

For tomatoes, some early overhead irrigation is used before transplanting but drip is the primary irrigation. Overhead irrigation is used for early cucumber establishment followed by drip irrigation.

Bed width and length, and the number of rows per bed, are carefully planned to fully utilize space, suppress weeds and make harvest as efficient as possible.

Shorter crops like baby greens are typically grown on a system of 30-inch beds with a 12-inch path for workers and eight beds per hoop house. The number of rows per 30-inch bed varies with the crop.

Lettuce is planted in three rows per 30-inch bed with an eight-inch, in-row spacing that aligns with the drip emitter spacing. Kale is planted two rows per bed with a 12-inch, in-row spacing. Spinach is planted in five rows per bed and baby greens in 16 rows per bed – both at tighter in-row spacings.

The ultimate goal is to maximize the linear feet of the beds and the linear feet of the rows on the beds. The system can be intercropped with beds of smaller, short-season crops and beds of taller, full-season crops to maximize production. This is important where the number of hoop houses are limited or entire houses of a crop can be planted all at once or in succession depending on marketing needs.

Tomatoes and cucumbers are typically grown on six-inch wide beds with a 36-inch path for workers. This puts the rows about 42 inches apart which puts eight rows per 30-foot hoop house. Tomatoes are spaced 16 inches in the row and cucumbers 12 inches in the row. Both of these crops are vertically pruned and trellised to overhead wires.

Peppers, a more medium-sized crop, is planted in three-inch beds with a 24-inch path which puts rows 27 inches apart. The peppers are spaced 12 inches in the row and basket woven.

Fabric hits the mark

The beds are marked out and then built with a bed roller. The Campus Farm uses landscape fabric that covers both the path and all but a narrow planting opening of three to five inches wide rather than plastic on the beds.

“Landscape fabric is more reusable and fits better,” Moghtader said. “We really like the ability to apply overhead irrigation at times, so we like the permeability of landscape fabric.” This permeability allows for the full wetting of the soil to stimulate microbial activity.

“We like the air flow through the fabric,” Moghtader said. “It also gives us solid walking paths that are weed-free.”

The landscape fabric also doesn’t have the cooling effect on early season soil temperatures that mulches like straw have. These cooling effects can slow plant growth in warm season crops like tomatoes and peppers.

The three- to five-inch open bed top between the pieces of landscape fabric also allows for sidedressing with dry organic fertilizer like bagged, composted poultry manure which the farm uses for higher biomass, longer term crops like trellised tomatoes.

The Campus Farm uses copious amounts municipal compost at start up. “Municipal compost has lots of leaves so it has less nitrogen than other composts but does have lots of organic matter,” Moghtader said. The organic matter really helps with water retention, soil structure, and nutrient holding capacity along with driving microbial activity.

“We put six inches down – or about 50 yards – along with any other needed amendments before the hoop house ever goes up,” Moghtader said. “This initial investment is worth it in the high-value production space. We want to be set for a long time.”

— Dean Peterson, VGN correspondent




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