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Seven Principles of Annual Hill Culture E. Barclay Poling Introduction. "Cultural practices in the years ahead, will be a living thing and subject to change, as technology changes, growers must change or be left behind." (Rotthoff, 1981) It is remarkable to think about Mr. Rotthoff's comment of twenty years ago, and to realize how much impact a newer technology, annual hill plastic mulch culture, now simply called "strawberry plasticulture", has had on fruit growers and nursery producers in the eastern US. In reference to the nurseries, the demand for matted row strawberry plants has declined to the point that most of the eastern strawberry nursery plant trade has shifted from Maryland to Canada and New England. There is only a small residual of matted row production left in the Southern States. North Carolina has actually climbed to become the fourth in the nation in strawberry production with an estimated 690 ha in plasticulture, or 1700 acres, and an annual farmgate value in excess of 14 million dollars. This is up from 2 ha (5 acres) in 1983 and 212 ha (540 acres) in 1990 (Poling, 1991). In more recent years, strawberry growers in northern states and colder mountain regions in North Carolina and Virginia (O'Dell and Williams, 2000) have started to adopt the strawberry plasticulture system as well. In this presentation I will discuss, with apologies to Stephen R. Covey (author of The 7 Habits of Highly Effective People), the 7 principles of annual hill culture: 1. Achieving large fruit size and excellent quality on a regular basis can only be achieved with first-year plants 2. Warm and mild winter growing areas can exploit the strawberry plant's natural tendency not to runner in the fall 3. The strawberry is a cool season crop 4. The strawberry is not a cold season crop 5. Plastic mulch technology is essential for full cropping in colder winter areas 6. Raised beds are just as important for full cropping as the plastic mulch film 7. Successful breeding programs are focused on annual hill production and give equal emphasis to cultural manipulations that can optimize plant performance Background on terminology and the first principle of annual hill culture. The term hill culture refers to a type of strawberry training system where the runners are either manually or mechanically removed (in summer), or don't develop at all (fall-winter season). It is a training system that allows only for the growth and development of the mother plant. Hill system transplants are normally set in double rows with plants spaced 12-14 inches in-the-row by 12-14 inches between the row - this is variety dependent as some varieties like Sweet Charlie benefit from closer spacings than more vigorous varieties like Chandler. Plants are normally set in a staggered pattern (offset) with the adjacent row. We attach the word annual to hill culture to describe a training system where new strawberry plants are set out each year for fruit production as opposed to training systems that take advantage of the perennial growth habit of the strawberry (e.g. matter row, spaced row, and ribbon row). In George Darrow's book, The Strawberry, he points out that you can find on Pacific Coast sand dunes examples of very old and woody strawberry crowns of Fragaria chiloensis that are as much as two feet in length (1966). Technically, there are examples of perennial hill-forming stands of strawberries in the wild, but in the commercial strawberry world, the three words, annual hill culture are used together to describe a hill training system where new transplants are set out each year - similar to an annual vegetable planting. In Florida, because strawberries are treated as an annual, university personnel working with this crop are actually in the Vegetable Crops Department! Where did annual hill culture first appear on a commercial scale in the United States? The answer is not North Carolina - we were a definite latecomer. But, in one historical reference I located, it is clear that idea of annual winter planting in hill culture was first recommended to California growers in 1916. However, as they say, the real reality is that annual winter planting was not commercially adopted until 1941 by Ned Driscoll who used it on the Tholke ranch. Wilhelm and Sagen, authors of A History of the Strawberry from Ancient Gardens to Modern Markets (1974) gave this description of that pivotal year in the history of the California industry: "Winter planting there resulted in high first-year yields of large fruit of excellent quality, and revolutionized the California strawberry industry. It led to the practice of planting fields solid, thus saving a year of tedious "catching down" of the runners from mother plants set several feet apart. To plant solid (in the hill system), about 25,000 plants per acre were required." The first and perhaps most important principle of annual hill culture is essentially captured in the above paragraph where it says that this newer system resulted in "high first-year yields of large fruit of excellent quality". This principle of annual hill culture can simply be stated as follows: Achieving large fruit size and excellent quality on a regular basis can only be achieved with first-year plants. Each time I read a report or hear someone mentioning their work to renovate and carry an annual hill plasticulture planting into to a second and possibly third year, I cringe. The main worry with any carryover program in the southeast is the very high potential of anthracnose infection in the summer season. If you carryover a first-year planting be prepared for smaller berries that are much more time-consuming to harvest. In a second or third year bed there is no practicable way to control plant density. And, without that control, you cannot regulate fruit size. Annual hill culture requires a fresh planting every year (in late-summer or early fall), not every other year! I understand the 'initial sticker shock' of new growers who are looking at the costs associated with strawberry plasticulture. Compared to matted row, it is a more costly production system. In the budgets we generated for our Summer Preplant Meetings in North Carolina this past summer (Poling 2000), it is clear that most growers are spending in the range of $6,300 per acre. If you add charges for row covers and special fumigation services, the cost can rise to about $7400 per acre. By far, the biggest expense item in the strawberry plasticulture budget is for plant material - $2500/acre or more for plugs! But, this is not the area to look for a shortcut. "What we're trying to do with annual hill culture is to exploit the juvenility of the first year plant," is a remark that Victor Voth, an internationally known University of California cultural researcher, made to me once on a visit to his test plots at the South Coast Field Station in Santa Ana. This is more than a casual observation - it is another way of understanding that the best "grower control" for optimizing fruit quality and size is to stick with the younger first year plants. Avoiding runners - the second principle. Twenty years ago, my first technician, Jerry Rogers, and I made an unsuccessful attempt at a spring-set annual hill cultural system in eastern North Carolina. This was before we understood the potential of fall-planting of fresh dug plants on plastic mulch beds. We learned that the manual removal of runners from the mother plants of a vigorous varieties like Atlas or Earlibelles every two weeks during the summer would be cost prohibitive for growers. The second reason we abandoned spring planting of matted row varieties in hill culture was related to the constant threat of plant infection with anthracnose, especially in the months of July and August. However, we did not totally give up on idea of hill culture as a result of this initial failure - we just had to smarten-up! I think it is very telling that at the 1990 North American Strawberry Conference held in Houston, Texas, that Dr. Royce Bringhurst, chose in his keynote address to recognize that a man by the name of Charles Peabody from Columbus, Georgia, first recognized in an 1860 essay the value of "a practicable system of plant density control for the life of the planting, approaching the "hill system" by commercially exploiting the strawberry plant's natural tendency not to runner after exposure to warm winter growing conditions." I wish that I had heard these remarks in 1980 when we were so unsuccessful in our attempt with a spring-set annual hill cultural system. By planting in the spring, it is possible to have the production of as many as 50 or more runners or daughter plants from a single mother plant! But, if your objective is to grow strawberries in the annual hill system in a warm (S. Calif., Fla.) or mild winter region (GA, SC, NC), then it makes eminent sense to wait until the late summer or early fall to plant when runnering has slowed down or stopped. As days become shorter and temperatures cooler, fewer and fewer runners are initiated by the mother plant. Usually, by late-September runnering ceases, and this is time when growers in the piedmont and cooler areas begin to plant. By the time growers in the southeastern Coastal Plain plant in mid-October, there is no runnering at all. Cool season crop - the third principle. Did you ever wonder why we cannot extend the cropping season of the annual hill plasticulture crop in the Southeast past early June? Even more northern Mid-Atlantic states like Delaware, Maryland and Southern New Jersey have great difficulty in trying to harvest past mid-June. The main problem is that temperatures simply become too hot for any further reproductive development. In fact, all reproductive activity essentially stops when the temperatures rise into the low 80s. By early May we can experience temperatures that are warm enough to not only abort remaining blossoms on the plant, but we can sometimes get hot enough to cause fruit scalding (as happened in the first week of May, 2000). If only we had temperatures in the low 70s every day during May, June and July, then it would no longer be necessary for buyers to go to Santa Cruz or Watsonville, California, for their summer berry supply! Clearly, the heat wave of early May (temperatures soaring into the high 90s) stands out as an example of how intolerant strawberry blooms and fruit are to extreme heat. The other less obvious example of the benefits of cooler temperatures came earlier this past spring - you may recall how cold and rainy it was during the last two weeks of April 2000? With night temperatures in the 40s and daytime temperatures in the 50 - 70 range, we had ideal conditions for further floral differentiation in the Chandler crop. This unusual cool spell helped us to recover from what could have been a financial disaster for a number of growers who were unable to fumigate and/or planted late in 1999 because of Hurricane Fran. The strawberry is not a cold season crop - the fourth principle. On the last day of October this year (Halloween), I received a rather startling call from one of our upper piedmont counties - the grower was calling to see what his options were if his "conditioned" Sweet Charlie plugs were just now starting to bloom? Realizing that he had purchased 10,000 of these specially conditioned plugs for fall fruiting, I was hopeful that he had erected some sort of tunnel enclosure that would allow these plants to go on and start fruiting in the next month. But, the fact of the matter was that he had not made any arrangements to put up either a low or high tunnel. This was a difficult situation, to say the least. The grower had already frost protected on several nights, and he wanted to know if he should just keep sprinkling on each night of freezing temperatures. In recent years we have experienced true Indian Summer fall and winter conditions that made it possible to see some late fall fruiting of so-called "conditioned" Sweet Charlie plants. But, what will happen if: 1) you don't have an Indian Summer type weather pattern; 2) your location is in the upper piedmont of North Carolina; and, 3) you set Sweet Charlie in early September for a fall/winter crop? The answer is that you are not going to get a fall crop in such a region without an additional investment in protective tunnels. There are numerous R&D type questions related to the potential for fall fruiting in the mid-South as well as valid concerns about overall economic feasibility of such a program. Here is what we do know from the best teacher, experience: 1) the strawberry is a cool season, not a cold season crop; 2) when night temperatures in early November begin to regularly drop below 40 F and the days are getting shorter and shorter, you can expect a marked slowdown in plant top growth and floral development - this is generally a good thing because we want the plant to acclimate for the upcoming winter; 3) the strawberry is a herbaceous, not woody plant, and its crown tissues are subject to greater cold injury if you are trying to force top growth just prior to winter; and, 4) the late fall and early winter period is the time of year when we wish to encourage extensive root development to build up the plant's capacity for producing a full crop the following spring. Plastic mulch technology is essential for full cropping - the fifth principle Late fall and early winter field conditions in North Carolina and the mid-South are actually too cold for the strawberry annual hill system to be economical without the addition of black plastic mulch. With Camarosa, it would appear that additional heat units are needed from late fall row covers, especially in colder fall seasons, to increase spring season fruit yield of this variety. In a warm winter growing climate, Southern California, Victor Voth pioneered the use of clear polyethylene mulches applied as soon after winter planting to promote early production and cleaner fruit in the 1960s. One of my favorite historical passages that identified the importance of plastic mulch in the mid-South was written by George Darrow (1966): "Black plastic in Florida and clear plastic in Japan and southern California are used to cover the soil, and the heat does not radiate so rapidly off the soil under the plastic, so that with several degrees warmer soil for several months, more extensive root and crown development occurs." Raised beds are equally important for full cropping - the sixth principle. I believe that it is just as instructive to look backward and see what George Darrow said about root growth to better appreciate the importance of raised beds, especially in the wetter winter months and during extended periods of frost protection. With the addition of raised beds to the total package, you can also see the name strawberry plasticulture, is preferred to the annual hill plastic mulch raised bed system! Roots of the strawberry grow chiefly downward in well-drained sandy soils and a few roots may be found as deep as 24 inches. In clay soils they spread more horizontally. In late fall when the water table rises and the oxygen in the deeper layers becomes low, root growth is shallow. The oxygen content of the air in the soil where root growth is active is nearly that of the air above the soil, but where soil is water, it may be as little as 1/10,000 the normal." Varieties must be bred for annual hill culture - the seventh priniciple I recently read with interest a statement in the Strawberry Production Guide for the Northeast, Midwest and Eastern Canada (1998) that: "Strawberries are extremely variable, and varieties have been developed for all parts of the world. But varieties tend to be narrowly adapted to specific regions. Varieities developed in one part of the world rarely grow well in another region" This last statement may hold true with matted row varieties, but the fact of the matter is that successful annual hill culture varieties from California are grown over the entire world, including North Carolina where Chandler and Camarosa are the main varieties produced. In annual hill culture all the rules have changed. In years past, matted row breeders would select a variety for a particular region that had both good plant-making abilities (for the matted row) as well as desirable fruiting characteristics. In fall or winter planting annual hill systems the plant production area is geographically separated from the fruiting area. Whether or not a selection has good runner-making characteristics for areas with hot and humid summers (southeastern US), is no longer an issue. In eastern NC, for example, we are primarily interested in good fruit size and consistent yields under our variable fall-winter-spring growing conditions. If a variety can withstand three straight days of rain during harvest season, that's something we are very interested in having in a new variety. In reality, I think this is one of the main strengths of Camarosa and the newer Gaviota variety from UC Davis, they both withstand wet weather remarkably well. I don't mean to minimize the importance of good runner-making characteristics or having high levels of disease tolerance bred into new varieties. But, commercial propagators of California short day varieties do not normally have problems with plant-making in the summer nurseries, and more than not, the difficulty of not enough runnering comes with the day-neutral varieites. Conclusion. Believe it or not, there are other principles of annual hill culture that I would like to identify, but in a thirty-five minute presentation, it is difficult to adequately address the 8th Principle - Fresh plant material (as opposed to dormant stored plants) grown in northern and high elevation production areas performs best in annual hill culture; or, the 9th Principle - Separation of plant propagation and fruit production phases is essential. Hopefully, the ninth principle is self-evident for disease control reasons, but it is interesting to look back to Ned Driscoll's growing days when it was observed that: "Nurserymen successfully met the challenge of having to adjust their plant-growing practices to the new needs (for annual hill culture). First, in order to supply plants for early planting, the nurseries left the floor of the Sacramento Valley and moved to mountain areas where elevations ranged between 2,000 and 3,000 feet. There, cold caused the plants to become dormant in the fall - usually by the last week of November - and thus ready for digging." (1941) Today it is interesting to note a parallel situation in the mid-South with virtually all transplants coming from colder regions just as they do for California fruit growers. There have been many more changes in the California industry since 1941 when Ned Driscoll took the initial plunge into annual hill culture. A significant change has been the increasing percentage of fresh vs. dormant-stored frigo plants that are now being grown by California nurserymen in response to Southern and Coastal California growers who need earlier and earlier fruit production to remain competitive (fresh plants are the key to earliness). In North Carolina, and throughout the mid-South and mid-Atlantic states we seem to be facing pressures of another kind - an increasingly unpredictable climate. I suspect that in the future we will be challenged to do even more with plasticulture and freeze control technologies to help minimize weather related crop losses. It was not until the end of the 1990's that we realized that the value of floating row covers is best realized under the threat of late winter advective freezes. In early March 1998 we demonstrated for the first time a successful strategy of coupling overhead irrigation with row covers to form an "ice blanket" to trap ground heat and to eliminate evaporative cooling problems under conditions of a severe windborne freeze (temp. min. -8.6 C, or 13 F) with minimal losses of strawberry buds (Poling, 1998b). In conclusion, my chief reason for giving this talk is my belief that growers who better understand the benefits associated with annual hill plant culture will be less likey to accept the tradeoffs associated with perennial plasticulture growing systems. It is also my belief that growers who understand what makes an annual hill strawberry plant "tick" will have a true advantage over the strawberry farmer who would rather just follow the recipe, or worse yet, a half-baked recipe! click HERE to return to proceedings page |
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