Tuesday, April 29, 2008


Overview Watermelons need an average of 4 months to mature, from 80 to 120 days. A loose, friable sandy loam soil is preferred: compacted layers can be very detrimental to root development.

Soil Watermelons thrive in fertile sandy loam soils containing organic matter with a pH of 6.0-6.5. Soils should be turned over 7-8” in the fall to allow for complete degradation of plant material and planting beds should be formed by one of three ways: Disking and subsoil bedding, disking and moldboard plowing and bedding, or disking, moldboard plowing, and subsoil bedding. For early production, plants should be planted on a raised bed. Disking after plowing should be avoided, because studies show that this process only leads to more compacting in the soil.

Another option of planting is hills. Hill formation should be formed on a 10 by 10 foot to a 12 by 8 foot row spacing and are formed by intersecting furrows.
Temperature The watermelon is a warm season annual. Therefore it prefers temperatures above 70° F for optimal growth.
Fertility Since watermelons are grown in sandy loam soils, leaching of minerals and nutrients can be quite a problem. Regular soil tests and tissue analysis should be conducted throughout the season.
When soil test levels are low, apply 120 pounds per acre of nitrogen, potassium, and phosphorus. It is recommended to apply a pop-up fertilizer 2-3” below the seed line before seeding or transplanting of approximately 100 to 150 pounds of 10-34-0. Current recommendations include applying phosphorus and micronutrients plus one third to one half of the N and K requirement from the soils test at planting and following this with two more applications at 3 and 6 weeks of the remaining N and K.

Of course these are only recommendations and results will vary widely between different soil types and areas. To be absolutely sure of nutrient levels, have soil tests and tissue tests performed regularly. It is recommended to perform tissue analysis on 8 to 12 day intervals.

Copper deficiency in watermelon. Weed Control Common weeds in the Southeast include Sicklepod, Yellow and Purple Nutsedge, Florida Beggarweed, and Cocklebur. Fields with perennial weeds such as bermudagrass should be avoided due to continued problems season after season.

The best method of weed control is a mixture of pre-plant mechanical weed control and post-plant chemical weed control. If cultivating for weeds after plant establishment, care must be taken not to disrupt the root system of the crop.

Cultivate only the top 2” of soil in the furrows. If hills are used, do not mechanically cultivate. If damage to the root system or to the stem occurs, rolling will begin to occur, essentially destroying vine integrity and thereby ruining fruit crop for that vine section.

In the fall, turn the soil over to a depth of 7 to 8” to bury and allow all vegetation enough time to decay. Contact your local extension office to find out what chemicals are currently approved for the control of these weed species.

Irrigation The watermelon is comprised of 90% water, approximately 4 gallons for a forty pound melon; therefore, water supply is critical during the growth and development of the plant and fruit. Water shortages will cause noticeable gaps in production with a reduction in leaf area and overall yield. Supplying water throughout the growth of the plant is important, but absolutely critical during flowering and development of the fruit.

Most watermelon fields in the south are irrigated through an overhead system. This can be a center pivot design, a linear move system (very efficient for rectangular shaped fields), a traveling big gun, or a permanent set of portable aluminum pipe and risers. Fertigation can be used with good results through this last method.

In Georgia, drip irrigation is becoming a popular method for irrigating watermelon crops. This method is very efficient for melon crops grown on plastic. Through drip irrigation, 40% less water can be used, fewer weeds are prevalent, and earlier yields are obtained. These benefits help dramatically reduce the cost of installing drip irrigation.

Watermelons transpire 0.3 inches per day. To account for this, irrigation should occur two to three times a week (in good weather) with 0.5 - 0.8 inches of water being applied at each application. The primary focus of irrigation is to keep the top few inches of soil moist at all times, but to keep the soil from being waterlogged.

For more precise irrigation scheduling, a tensiometer or similar field device should be used to determine available soil moisture. From this data, scheduling can be used to water only when needed, thereby saving even more in irrigation costs. Remember to apply 10-20% more than transpiration needs to account for wind drift and evaporation. Drip irrigation will need to be operated more frequently than overhead due to the nature of the water flow confined to the root zone.

Turning Watermelon vines need to be ‘turned’ or adjusted to keep the runners in the proper direction. This allows for clean furrows for movement and cultivation between plants without damaging the vines. This turning should occur before runners are established with adventitious roots and should only occur once per runner to prevent damage and rolling of the vine.

Pruning Watermelon plants need to be pruned of excess fruit to allow the correct number of fruit to properly develop and obtain marketable size. Pruning should occur in two stages. The first pruning removes all of the culled (unmarketable) fruit while the second removes the late set fruit in order to increase the size of the remaining melons. There should only be 2 melons per vine (5 per vine for icebox varieties) after pruning.