Large, juicy watermelons (Citrullus lanatus) provide a summer treat in the vegetable garden, but a weed invasion can reduce your crop. Watermelon can't compete well with weeds for water and nutrients, especially when the plants are young. Plastic mulch can prevent nearly all weed growth, but you can also reduce weeds in established beds when it's too late to add plastic. Mulching for weed control also provides other garden benefits, including cleaner fruit, warmer soil and increased soil moisture.
Lay drip irrigation or soaker hoses down each watermelon planting row prior to mulching. Space the rows of hose 4 to 6 feet apart. Water doesn't penetrate plastic, so irrigation must take place beneath the mulch.
Place a sheet of black plastic mulch over the prepared bed. Overlap sheets of plastic by 6 inches so there is no seam for weeds to grow through. Anchor the perimeter of the plastic with U-shaped garden stakes spaced at 8-inch intervals. Insert additional stakes along the overlapping edges so these are well anchored.
Make a series of "X" cuts into the plastic with a utility knife along each row for the watermelon plants, next to the irrigation hoses. Space the cuts 2 feet apart. Fold the flaps formed by the cut under and plant the watermelon seedlings in the holes.
Inspect the visible soil around the base of each watermelon plant weekly, and pull any weeds that grow in the exposed soil. Once the watermelons reach their full size they will smother out any weeds that attempt to grow near their bases.
Break up the top 1 to 2 inches of soil between the watermelon rows and young plants with a hoe. Repeat one to two times a week so weeds are disturbed before they establish deep root systems.
Cover the bed with a 2- to 3-inch layer of straw mulch once the plants grow tall enough that they aren't smothered by a mulch layer. Pull the mulch back slightly from the base of each watermelon so it doesn't rest against the plants. Mulch suppresses most weeds.
Inspect the watermelon bed weekly and pull any weeds that grow through the mulch layer by hand. Grasp each weed near its base and pull it straight up, twisting slightly to dislodge deep roots without breaking them.