Field Prep And Plastics

Believe it or not, the optimal time to get your fields ready for spring planting under plastic film may have already come and gone. Take heart, though, you may still have time to do something about it.

According to Tim Coolong, assistant professor and Extension vegetable specialist in the Department of Horticulture at the University of Kentucky, late fall and winter is often the best time to ready fields in order to lay plastic for the earliest spring plantings.

One of the reasons growers choose to grow under plastic is to be one of the first in the area with produce in the spring. For growers looking to take advantage of the early market, Coolong offers 10 pointers that will help them meet with success.

#1  Ensure a fine tilth of the soil.
Growers need to get the ground prepared fairly deeply, especially if they are doing raised bed production in the spring with plasticulture. “If they don’t have a finely prepared soil — but rather soil that is cloddy and has a large, blocky structure to it — and they try to lay plastic over that, the result will be a poor bed,” Coolong explains. “By not pulling the plastic tightly up against the soil, air will be trapped between the plastic and the soil. That air can heat up and can burn plants.”

#2 Have good contact between plastic and the soil and use the proper equipment to lay the plastic.
As mentioned above, the plasticulture system doesn’t work as well if you don’t have a tight connection with the plastic and the soil. Coolong tells growers to use a tractor with enough horsepower to be able to sink the bed shaper to form a tight bed. “Some growers have used an underpowered tractor to run the plastic and they can’t get enough soil in the bed in the center, which can cause pooling of water in beds as well as a buildup of warm air under plastic that can damage plants,” he explains. “It is also important for growers to make sure the discs on the bed shapers are adjusted properly so they fill the center of the bed with soil.”

For growers using a larger sized bed shaper/plastic layer, the accompanying tractor should have a minimum of a 50-horsepower engine. A 65-horsepower tractor will do an even better job, creating straighter rows and a better quality bed, Coolong adds.

#3 For crops planted later in the season, use white on black plastic.
Black plastic is typically used for first plantings. For subsequent plantings, such as in the last week of May or first week of June, growers should use white on black plastic. “By using white on black, they will get much better transplant survival and better yield because at that time they don’t need the soil warming properties of the black plastic,” Coolong explains.

#4 Lay plastic before winter, if possible.
Part of the reason growers need to get the ground ready before winter is because spring rains make it difficult to plant vegetable transplants, he says. If time allows, however, some can lay plastic in mid-winter.

#5 In mid-summer it is best to use short, raised beds or flat ground.
“Earlier in the spring, many growers do a much taller raised bed than they do in mid-summer,” he says. “The reason for that is the taller the raised bed, the more surface area you have for solar radiation to intercept that bed, allowing it to heat up substantially quicker. As you get to mid-summer, however, you don’t need that soil heat as much. In fact, raised beds tend to dry out quicker. As a result, some growers are going to very short raised beds or even flat ground for plastic production in mid-summer, which may help them conserve water.”

#6 Conduct soil sampling tests in the fall.
Coolong tells growers to get soil sampled and tested in the fall so they can apply amendments prior to planting. “Some growers will get a soil test and get results back after laying their plastic and they find that their pH is low,” he says. “At that point, there is no way they can put those materials through the irrigation system.”

#7 Implement the stale seedbed technique for weed control.
As weed control is always an issue, Coolong encourages growers to use the stale seedbed technique. “You will have a flush of weeds as you prep your ground, allowing new weed seeds to come to the soil surface,” he explains. “Those seeds will germinate as they get water from rain. Once weeds come through, growers do a light cultivation and then lay plastic,” he continues. “The alternative is to lay plastic and allow that flush of weeds to come up before planting.”

After that, growers can go in and cultivate between rows. This technique cuts down on weed pressure between rows, he adds.

#8 Plan crop rotations to allow for double cropping on plastic.
In Kentucky, Coolong says many growers plant a spring cole crop and later do a fall planting of cucumbers, or a similar crop. By having a plan with crop rotations, growers will spread the cost of the plastic over two crops, saving money and creating efficiencies.

#9 Remove plastic in time to seed a cover crop in the fall.
Coolong encourages growers to remove plastic from the field early enough in the fall so a cover crop can be planted. “Most growers try to push their season for as long as they can,” he says, “but if they push the season into late November it is often too late to plant a cover crop. By not planting a cover crop, growers aren’t building soil effectively for future crops.”

#10 Use hardened off transplants.
Plastic tends to get very hot in late spring on clear sunny days. As a result, transplants that have not been properly hardened off can be damaged from the heat. To maintain a healthy crop, Coolong tells growers they need to give greenhouse plants time to acclimate to living in the open field.