Transplanting Plugs. The ideal age of the plug for field transplanting is four weeks. Plugs held for six weeks in the trays are not as desirable and may have a slower initial growth rate in the field following transplanting. Plug plants pose less serious problems than freshly dugs for field transplanting. Pot-mulch planters or vegetable water-wheels can be used to mechanically transplant and water strawberry plugs. Careful size-grading of tip plants will produce more uniform plugs for efficient machine transplanting.
- Depth. Do not “bury” the growing point of the plug plant by setting too deeply. Plug plants are not very deep; the rootballs are only 2¼-inches in depth for 50-cell trays. The planting hole should not be quite as deep as the plug rootball. A 2-inch hole is recommended for a 2¼- to 2½-inch rootball. Press the plug into the hole so that the top of the rootball is about even with the soil surface. Even if you are mechanically setting plugs with a water wheel, it is a good idea to have one or two workers following the transplanter to brush a light layer of soil around the top of the plug’s rootball without covering the growing point. This soil layer is helpful in keeping the plug moisture from “wicking out.” Without this slight soil layer, moisture will be wicked out of the exposed rooting media very rapidly on sunny, windy days.
- Starter Fertilization. Tray-grown transplants that have been under a plug propagation nutritional program do not require a starter solution at transplanting. A typical feeding program for plug transplants while they are still in the trays is to apply 1 pound of 20-20-20 per 100 gallons of water (in weeks three and four) before transplanting. This supplies roughly the equivalent of 240 parts per million (ppm) nitrogen.
- Irrigation. A few hours of overhead sprinkler irrigation immediately following transplanting of plugs is recommended. A number of commercial growers in North Carolina use light overhead sprinkling (1/10-inch per hour) for the first, second and possibly third day following transplanting for approximately 5 hours, 3 hours and 2 hours per day, respectively.
Establishing Fresh Dugs. The establishment procedure for highly perishable freshly dug transplants depends on intense overhead sprinkling for one to two weeks, depending on weather and plant condition. Fresh dugs exposed to cooler temperatures or chilling in the nursery (or both) will require less time for establishment than fresh dugs produced in warmer climates.
- Storage and handling. Fresh dugs may be stored in a cold room at 38oF for 1 to 2 days before setting; for storage of up to a week, the cooler temperature should be 34oF. Storage for a longer period can make the plants more difficult to establish. Plants in a nursery box or crate are packed tightly enough (typically 500 to 1,000 plants per crate) to make them prone to what is called a “heat,” which makes them unfit for subsequent planting in the field. It is very important to cool the plants prior to transit. During hot weather it may be necessary to put plant boxes out to cool more quickly in the cold room or run water through the crates to keep plants cool if a cooler is unavailable.
- Root pruning. Some root pruning may be needed to shorten roots to 5 to 6 inches prior to transplanting.
- Transplanting. The freshly dug strawberry plant is hand-transplanted through the plastic mulch in 2½-inch slits cut by specially constructed spacing wheels that also open a narrow hole for planting. This equipment can substantially reduce the number of hours required to set one acre of fresh dug strawberries (approximately 40 hours per acre). Do not punch holes through the plastic more than two days ahead of planting. Set the plants so that the midpoint of the crown is level with the soil surface. If plants are set too deep, the plants are unthrifty, and crowns may rot and die. If planted too shallow, the root system is exposed, which can result in poor rooting and shifting of the plants. The roots must not be J-rooted when set in the planting hole. Often plants may be set at the right depth, but may either be in a small depression or have soil ridged around the crown. When irrigation is started to establish plants, the depression can fill and bury the crown or the ridge may erode and expose roots. A firm plant bed will assist in preventing the bed from settling or eroding. Refer to this step-by-step illustrated guide for setting freshly dug plants in English or Spanish.
- Bicycle wheels for spacing. There are several drawbacks associated with using traditional fresh dug spacing wheels. In extremely wet seasons, the fields remain too wet for operating any tractor-drawn equipment. Ironically, the same wet conditions that prevent running equipment through the field are generally very favorable for establishing transplants. To avoid further delays in planting, a solution was pioneered by Keith Hill, a grower in Smithfield, North Carolina. Hill designed a lightweight unit consisting of two bicycle wheels that are mounted in tandem on a steel frame. This unit can be pulled by hand over the tops of the plastic-covered beds. Unlike tractor-drawn spacing wheels that cause the plastic to stretch and then leave a larger than necessary tear in the film, the bicycle wheel rides over the top of the plastic film. Carriage head bolts, protruding through each tire, mark the location for planting with just a small hole or prick in the plastic every 14 inches. The bolts are inserted through pre-drilled holes that are spaced to achieve the desired in-row spacing. The bicycle wheels are 12 inches apart (the desired spacing between a double-row of plants); and the wheels are rotated and set to achieve a staggered double-row planting pattern as a worker pulls the unit over the bed top. If you use a 12-inch in-row plant spacing, for example, and also want the wheel to mark four holes per complete turn, then you would need to use a 15.27 inch diameter bicycle wheel (12-inch in-row spacing times 4 holes divided by 3.1416 = 15.27-inch diameter bicycle wheel). With some minor adjustments, this unit also can be used on a conventional fresh dug spacing wheel frame to mark plant holes using a tractor.
- Hand tool for setting. A good tool for setting fresh dugs can be made by bending a piece of 3/16-inch thick steel (1 3/16-inches wide) at a 90-degree angle such that there is a 4½-inch handle and an 11¾-inch shaft. A notch (about ½-inch deep) is cut into the base of the shaft to aid in catching and holding the bottom of the roots as a worker guides the plant’s root system straight down into the soil to a depth of about 5 to 6 inches (depending on root length). A narrow piece of foam is often placed on the shorter end of the tool and wrapped in duct tape for a more comfortable grip. The tool is ideal for setting fresh dugs because it simply makes a slit (no wider than 1½-inches) through the black plastic. The idea is to keep as much of the black plastic intact as possible. Larger holes (such as those made by conventional spacing wheels) will lead to weed competition soon after planting, and side branch crowns will not get caught under the plastic. Many growers are surprised to learn that you can achieve a much better transplanting job with fresh dugs by using this special hand tool in conjunction with the bicycle spacing wheels to mark the holes. Refer to this reference with illustrations for using the hand tool.
- Irrigating. Start overhead irrigation as soon as plants are set-no more than 30 to 45 minutes should elapse. These plants will require irrigation varying from 7 to 14 days after transplanting. Irrigation for the first several days usually begins no later than 9 a.m. and will run continuously until 5:30 p.m. Each morning, start irrigation when plants show moderate wilt, and continue to irrigate until the hot part of the day has passed. After several days, irrigation can be initiated a little later in the morning and can be discontinued earlier in the afternoon. The primary purpose of these irrigations is to prevent foliage loss until the root system can develop and absorb sufficient moisture to sustain the plant. Plants should have three or more fully green leaves remaining at the end of the establishment period. Only a relatively small volume of water is required for mist cooling. Growers at N.C. State have been successfully using 1/10-inch per hour.