Vegetables and Ornamental Horticulture : Plastic Mulch and Drip for Pumpkins

Plastic Mulch and Drip for Pumpkin Production

Brent Loy, Department of Plant Biology University of New Hampshire

Improvement in production systems for pumpkins has lagged behind that of most of major vegetable and agronomic crops. This may in part be due to the fact that pumpkins are a fall crop, and with vegetable farmers growing a diversity of crops, pumpkins often get neglected during the period when the harvest of other crops is in full swing. When I came to New England over 30 years ago, many growers were using a wide spacing (12 x 12 feet), and planting pumpkins in hills of 2 to 4 plants. This system or variations of it still persists among many growers. Of course, the basic premise of this system is that you can cultivate in both directions and the huge pumpkin vines will eventually fill up the space.

According to recent figures released by the USDA, pumpkin acreage in the U.S. has tripled since 1982. Coincident with this increase has been a huge increase in the number of pumpkin varieties, and increased research on cultural and IPM methods for pumpkin production. Pumpkin trials in several states have shown that higher fruit yields are obtained at closer than conventional spacing. Most recommendations would be to space rows 7 to 8 feet, and plants within the row 2 to 4 feet apart, depending upon the variety and the size of pumpkin that is desired. Obviously, for growing really large or show pumpkins, much wider spacing is needed. A closer spacing results in faster leaf canopy cover for more efficient photosynthesis, and also with timely cultivation, the rapid growth of a dense plant canopy can suppress weed development.

Plastic mulch and drip irrigation is compatible with the higher density planting that is being recommended for pumpkins, and also works well with the semi-bush F1 hybrid varieties that are gaining a bigger portion of the pumpkin market. To produce F1 hybrid pumpkin seed cheaply, it is usually necessary to use a bush or compact strain as the female parent. The bush strain is then crossed with a vine strain to produce a bush x vine F1 hybrid. These hybrids have a compact uniform habit of growth early in the growing season, but by midseason the vines begin to run. If these semi-bush hybrids are spaced 2 to 3 feet apart within a row that has been mulched with black plastic, they will form a dense leaf canopy over the plastic within about 5 weeks from seeding. If the rows are spaced 7 feet apart, then the approximately 4 foot width of bare soil between the mulch can easily be kept weed free by cultivation with a small tractor. Shortly after the vines begin to run off the edge of the plastic, a final cultivation is made, along with some hand hoeing along the edge of the plastic. Within two weeks, before appreciable germination and growth of weeds has occurred, the plant canopy will largely fill-in between the mulched beds and shade out further weed development.

Combining drip irrigation with the plastic mulch is an additional refinement of pumpkin culture that can be highly beneficial, especially on lighter soils. Irrigations can be timely without the necessity of moving pipes, and better control of foliage diseases is usually afforded because additional water is not being applied to the foliage. Pumpkin plants are fairly deep rooted and the maturation period for pumpkin fruit is mulch longer than for other crops such as tomato and melons, so that irrigations can often be made less frequently. Furthermore, it is more convenient to add fertilizer through drip than through overhead irrigation. Because of the convenience of drip irrigation, irrigation can be scheduled during busy periods when overhead irrigation might be out of the question.

The first 30 to 35 days of fruit development following pollination are especially critical in pumpkin. Most of the fruit growth occurs during the first 20 days after pollination and maximum dry matter of the flesh is achieved by 30 days after pollination. Thus, if plants are kept healthy during this period, it will assure maximum fruit size and the stems will be sturdy and remain so as the fruits change color from green to orange. A pumpkin handle is a good diagnostic tool to ascertain health of a pumpkin crop. If pumpkin stems shrivel after short term storage, then you can be fairly certain that plants were under stress during the 20 to 35 day period following fruit set. There are, however, some semi-bush F1 hybrid pumpkins that either set fruit too early before adequate vegetative growth has been achieved or set too many fruit for the size of the plant. In such situations, the fruit requirements for photosynthates exceed the total needs of a plant for proper fruit, leaf, stem and root maintenance. This will often lead to premature senescence (aging and death) of plants and consequent problems with proper fruit maturation. Some of the better semi-bush hybrids have been bred so as to produce a robust leaf canopy and continued development of vines well after fruit have been set. This helps to assure that leaf photosynthesis is not limiting for supplying assimilates (sugars) to developing fruit and the root system. Growers may have to trial several semi-bush hybrids to determine which varieties are acceptable for their particular soil and climatic conditions.

Other advantages of semi-bush as compared to vine cultivars are that they usually have earlier maturity, fruit is more uniform and fruit size can be controlled to some extent by plant spacing. Certainly, vine cultivars can be used on plastic mulch and with drip irrigation. However, the direction of vine growth is random with vine cultivars and can lead to temporary gaps in leaf canopy cover, allowing weeds to compete more effectively. One advantage of vine cultivars is that they can withstand stress better than bush cultivars because of a higher ratio of vegetative to fruit growth and a more extensive root system because of roots developing at leaf nodes touching the soil. This difference in stress tolerance between bush and vine varieties is less of a factor when using plastic mulch and drip irrigation, because plants are generally healthier with this cultural system. In terms of productivity, some of the older open-pollinated, highly vining varieties yield as well if not better than the new hybrids. So in adopting a new variety, there may be some tradeoff between yield and a more desirable plant and pumpkin type.