Whenever I think about potatoes, I am instantly transported back to the little town of Augher in Northern Ireland where my great-grandfather William Lamont was the coachman for the castle. He and his wife had five Irish lads and one Irish lassie. He owned 11 acres of land, and I’m sure he raised some beef and maybe a dairy cow or two, some chickens and a big vegetable garden with a good size planting of potatoes. My grandfather William emigrated to America at the turn of the 20th century; today, one of my Irish cousin’s husbands raises cattle and is a potato farmer, growing a variety called Rooster that commands over 40% of the potato market in Ireland.

Over the years I have conducted extensive research, led workshops, spoke at numerous grower meetings and written extensively on the production of potatoes – the “pommes de terre” or “apples of the earth.” I am especially interested in early and specialty potatoes. I’m going to share some thoughts on early potato production drawn from my writings (in particular, “Growing Potatoes Using Plasticulture” from Penn State).

The production of early potatoes for direct marketing to consumers can be a very lucrative enterprise for those who only grow one to five acres of potatoes. Many places in late spring/early summer find consumers anticipating the arrival of “new potatoes” or “B”-size red potatoes. These early potatoes command a high price and with the increasing popularity of specialty potatoes (different colored skins and flesh), growers are now able to offer an increasing colorful array. To be able to provide high quality early potatoes, an increasing number of growers have turned to intensive production technology or plasticulture (plastic mulches, drip irrigation, fertigation, high tunnels and row covers).

The primary benefits of using plasticulture for potatoes is earlier production, greater yields and higher quality. Advantages of plasticulture are black plastic mulches warm the soil earlier in spring, which in turn hastens the emergence and development of potato plants and prevents weed growth in the rows; drip irrigation in conjunction with plastic mulches offers excellent control of soil moisture and the ability to fertigate; elimination of hilling; and potential reduction in disease pressure as well as the opportunity for insect management.

Over the years we evaluated the following potato varieties using this system: Keuka Gold (light-yellow flesh with white skin), Dark Red Norland (white flesh with red skin), Eva (white flesh with bright white skin), Michigan Purple (bright white flesh with purple skin color) and Red Pearl (white flesh with red skin producing 71% B size potatoes).

The plastic mulch/drip tape applicator used in vegetable production is also used for potatoes. The raised beds are four inches high and 30 inches wide with the drip tape buried three inches deep in the center of the bed. Drip tape used is 8 mm thick, has a 12-inch spacing between the emitter openings and a flow rate of 0.45 GPM/100 feet of row. Seed pieces can be hand-planted using a bulb setter to make the holes for very small plantings; larger plantings (three to five acres) can be planted in double rows 18 inches apart with 12 inches in row using a waterwheel planter without any application of water at the time of planting.

It’s important to have adequate soil moisture prior to making the beds and applying the plastic mulch and drip irrigation tape to ensure that the hole made by the waterwheel transplanter will not collapse before the seed piece can be placed.

(Side note: We developed a transplanter that utilizes cone-shaped dibbles that can punch holes in the plastic bed and can make holes four, two or one across, depending on the crop, and in-row spacings from six to 24 inches. It showed a lot of promise for not only potatoes but other vegetable crops as a replacement for the waterwheel, but it never went beyond the research stage. It is still available for someone to work on and possibly market. If anyone is interested, contact me and I will put you in touch with the person that has the planter now.)

Prior to making the beds and applying the plastic mulch and drip irrigation tape, fertilizer can be broadcast. An example used in our plantings is for 450 lbs./acre of 34-0-0, 500 lbs./acre of 0-10-10 and 500 lbs./acre of 0-20-10, broadcast evenly across the field. Spacing between the mulched beds is six feet. Though the distance between the mulched beds could be decreased to five feet apart, the plant canopies of the potatoes will quickly cover the space between the rows and can limit the air circulation that’s needed for disease control.

Floating row cover material could be applied once the potato seed pieces are planted. Chemicals can be injected through the drip irrigation system for control of some insect pests, then standard pest management practices can utilized the remainder of the growing season. When counting Colorado potato beetles, varying numbers of adults were found on the different plastic mulches evaluated in one experiment at the end of May: black mulch, 94 beetles; red mulch, 54 beetles; no mulch, 36 beetles; and reflective silver mulch, 13 beetles.

To take advantage of the different skin colors, an American flag made of the potatoes was constructed to show how they could be promoted in a retail market. Photo by Bill Lamont

When the tubers are nearly marketable size the vines can be killed using two applications of Diquat. The potatoes are dug using a double-row level bed digger and then picked up by hand. Potatoes set right out on the edge of the bed. Harvest began with Dark Red Norlands, then Michigan Purple, Red Pearl, Adirondack Blue, Keuka Gold and Eva. Although the plastic mulch and drip irrigation tape will travel up the digger chain, it’s easier to remove the plastic mulch prior to digging. This is best accomplished by mowing the dead potato vines as close to the plastic as possible with a rotary mower and then loosening the soil along the edges of the plastic and either removing it by hand or using a small retrieval unit that will make a small round bale of plastic.

All plastic mulches significantly increased total and marketable yields for all varieties compared to bare ground. Marketable yields for potatoes grown with plastic mulch as compared to bare ground: Dark Red Norland – black, 271 cwt., no mulch, 173 cwt.; Keuka Gold – black, 357 cwt., no mulch, 262 cwt.; Eva – black, 325 cwt., no mulch, 182 cwt. The same holds true for Michigan Purple, Red Pearl and Adirondack Blue. The increased yields more than pay for the additional cost of the plastic mulch and drip tape.

The bottom line is the fact that the rate of emergence and growth of sprouts from the seed piece once it is planted is mostly a function of the soil temperature. It’s important to remember that the bare ground potatoes also received drip irrigation, so the yield response is mainly a result of the plastic mulch. Plastic mulch and drip irrigation should be used together to get the maximum benefit from the system, and black plastic mulch is best since it prevents light from reaching the tubers and greening them. The skin colors were excellent on all varieties.

You can contact me with feedback on my columns or ideas for future columns at wlamont@psu.edu.