Watermelon Planting Guide

Watermelon Planting Guide

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Everyone wants to grow watermelons in their garden, and when children come into the store with their parents, it’s the first word out of their mouth when asked what they would like to grow. However they are one of the most demanding and difficult fruits to grow successfully. Timing, conditions, and weather all have to come together for just the right circumstances - but there are a few tricks we have up our sleeves to encourage these tasty treats to make our garden the envy of the neighborhood. Most watermelons have red flesh, but some have yellow or orange; they also come in many sizes from small, ice box size to gigantic 25-30 pounders - and who doesn’t want a seedless watermelon?

Soil Preparation

Watermelons prefer a sandy soil, rich in organic matter, well drained, and not too heavy. They also need full sun exposure. Before planting, incorporate 1-2 inches of well composted organic matter, Humic, and 1 lb. of all-purpose fertilizer (we recommend “That’s all it Takes” complete fertilizer or Happy Frog Organic Tomato & Vegetable Food) per 100 square feet and work them in to a depth of 4-6 inches. Heavy, clay-based soils must be amended with compost and organic matter to encourage and allow for good root development. For best results, add 2-4 inches of a variety of different types of organic matter and 50 lbs. of Zeolite soil conditioner per 100 square feet each fall for multiple years to increase drainage and nutrient availability. By doing this yearly, over time you can create a better growing environment for your garden plants to thrive in and produce. Please consult our Soil Preparation Guide in the attached appendix.


We have had success both from transplant or from seed when planting watermelons - but in both cases, it is best if you start by solarizing your soil with black or clear plastic mulch or weed barrier, 2-3 weeks before you want to plant. If starting seeds indoors, choose a warm location for germination (at least 75 degrees) and use a light seed-starting soil. We start our seedlings 3 weeks before setting them outside, so for Cache Valley, the last week of April is perfect. Just after Mother’s Day, cut holes into your plastic or weed barrier mulch at 4-6 foot intervals and then plant your seedlings the same depth as they are in their containers, and water them thoroughly with Kangaroots root stimulator. The Kangaroots will help prevent transplant shock and aid in establishing an extensive and strong root system quickly. If starting from seed directly in the garden, use the same spacing and planting time as for transplanting. Make a shallow depression in each cut (in the plastic mulch), place 4-6 seeds in each hole, and cover them with 1/4-1/2 inch of peat moss, light potting soil, or Coconut Coir, and tamp the soil down gently with your hand. Water with the Kangaroots, and cover the area with a hot cap, Wall-o-Water or Aquadome to help retain the heat and moisture. The seedlings should emerge in 7-14 days with adequate heat.


When it comes to melons, everyone has an opinion on which is their very favorite, and watermelons are no exception. At Anderson’s Seed, hands down, our favorite melon for flavor and quality is Yellow Doll. It’s early maturing, has bright yellow flesh, which is difficult for some people to fathom (watermelon is red, right?), but the taste is truly amazing. They also sell like crazy at the Farmer’s Market when you share samples.... For traditional, red-fleshed melons, try either Sangria (large, dark green rind, exceptional flavor and texture) or Royalty (probably the darkest red and sweetest melon we’ve grown) - they both mature in about 85 days. Early maturing Tiger Doll is one of the quickest and tastiest melons we’ve grown and probably a safe bet to start your melon growing experience with this one. It’s the easiest to get to mature in Cache Valley. Triple Crown is an excellent quality, sweet fleshed, seedless watermelon. Don’t try growing it until you have mastered the Tiger Doll or Yellow Doll first - the seeds are expensive, and later maturing melons are more tricky to grow. Don’t forget they need a pollinator as well!


Watermelons require frequent watering during the year, usually about 1-2 inches per week in 2-3 applications. Use drip or soaker irrigation if possible, and mulch heavily around the plants with an organic mulch to help retain soil moisture and to prevent weed emergence. Watermelon have a shallow root system, so be careful when cultivating close to the plant, and during warm, dry weather, they are prone to dry out quickly. We can’t stress enough the importance of using plastic mulch or weed barrier around the melons to prevent weeds, to heat up the soil, and to prevent damage from rapid drying and moisture loss. Consistently moist, but not soggy - that’s your goal.


About 4-6 weeks after germination or transplant, usually about the time the vines start to run, apply a balanced vegetable food (“That’s All it Takes” or Happy Frog Organic Tomato & Vegetable Food) around the base of the plants and water thoroughly. Use about 1/4 cup per hill. For some quick growth, especially around the time they start to flower and set fruit, use Ferti-lome Blooming and Rooting water soluble fertilizer or an organic alternative like Seedlinger’s Universal Plant Food weekly to kick them into fruit production mode. Since melons are so difficult to cultivate, we always recommend an application of beneficial microbes and mycorrhizae (Kangaroots or Myke supplements) to help with their development. Your plants will be healthier, more vigorous, and produce fruits faster and for a much longer harvest.

Common Problems

Not too many insects bother melon vines, but watch for cucumber beetles, aphids, and spider mites specifically. Mites can damage leaves quickly without notice, sapping vital strength from the plants, and severely limiting your fruit production. Ferti-lome Spinosad Soap (organic) insecticide or Triple Action Insecticide will be your best options for controlling these pesky invaders. Powdery mildew is almost as destructive to the vines and their productivity. In late July (or earlier if the weather is hot and humid with cool nights) start spraying the vines with Fertilome Fungicide 5 to prevent mildew from ruining your crop in August and September. All it takes is a week or two of mildew to stop the vines from flowering, and more importantly, stop the fruit production. Use crop rotation, water root systems and leaves with Fungicide 5, and use mycorrhizae to help prevent the vines from picking up Verticillium and Fusarium diseases that will quickly kill the vines just as they start to produce.


Knowing when to harvest watermelons is the most frustrating part of growing them. You watch them mature, and they look perfect, and you pick it, expecting this wonderful flavor, and it’s either too ripe and mushy, or firm, green and tasteless. Here is the secret to picking a ripe watermelon - and it has nothing to do with thumping the exterior for a nice hollow sound.... Two things need to happen for the melon to be ripe. First, watch for the color of the underside of the melon to turn from white to a creamy yellow color. When immature, the color under the melon will be a stark white, when it changes color, that is one indicator. Second, where the melon is attached to the vine, there is a small, corkscrew shaped tendril that grows off the vine itself. When that tendril (it looks like a pigs tail) drys up and is brittle, that is another indicator. For the melon to be ripe, you need to see both indicators - one just isn’t enough. When ripe, use a knife or hand pruner to cut the melon from the vine, leaving about 1” of stem on the fruit. Then, enjoy the best melon you’ve ever had from your own garden.

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