Watermelon FAQ – Plant Care & Growing Tips

The following tips and advice will help to grow strong healthy watermelon plants. You might also be interested in “How to Grow Sweeter Watermelons“.

Watermelons sweetness is measured by brix level. 1 brix is 1 gram of sugar per 100 grams of liquid. A good brix level for watermelon is 12 and anything 14 and above is excellent.

How Often to Water Watermelon Plants

Watermelon plants should be watered with 1″ of water a week until flowering and fruiting and then 2″ a week until watermelons get to golf/softball size and then back to 1 ” for 7-10 days and then don’t water at all 10-14 days before harvesting.

Flowering and fruit setting is when the plant is the most demanding and this time coincides with hotter weather in most growing areas. By not watering right before harvesting the watermelons sugar levels become concentrated.

Best Soil for Watermelon

Watermelon do best in sandy loam soil. Loam soil is a mixture of sand, silt, and clay. The size difference of the three particles in the mixture create good aeration and easy travelling for water and plant roots. A sandy loam soil is a mixture that is a higher percentage of sand. Most vining plants like a sandier soil.

If you’re buying potting soil Miracle-Gro potting is a good standard choice and the mix comes with enough nutrients to sustain plant growth for 6 months. 

Organic Plant Magic is a good organic potting soil with enough nutrients to last for months and beneficial bacteria in the mix.

Using potting soil is expensive but it is “perfect” soil for most garden plants with nutrients already added. If you want to amend your own soil adding organic material, compost, is the best way to do so over time.

mulch pile sign

You can gain access to large amounts of compost by calling local city governments and finding out where they have their compost piles. Usually the city picks up leaves and grass clippings and has huge aged piles of these where you can get as much as you like.

Best Fertilizer for Watermelon

Watermelons, like other garden plants, require a mix of major and minor nutrients that most fertilizers provide. Providing a good all-purpose fertilizer throughout a watermelons growth will yield good results.

Two more advanced moves you can do with fertilizing watermelons is to switch to a fertilizer with a 1-2-2 ratio once flowering and fruiting begins and to add boron as boron deficiencies are known to cause bland watermelons.

This soil test kit will provide soil PH and the levels of 13 nutrients in you soil including boron.  Jack’s Classic is a good all-purpose standard water soluble fertilizer and Organic Plant Magic is my favorite all-purpose organic fertilizer because it has a lot of different organic materials in it and 10 strains of beneficial soil bacterias.

Most fertilizer list the N-P-K, Nitrogren-Phosphorous-Potassium, the three major nutrients for plants. One with a 1-2-2 ratio would have twice the value of phosphorous and potassium to nitrogen, like the 5-10-10 Lilly Miller fertilizer. Nitrogen fuels vegetative foliage growth while phosphorous and potassium are more helpful for root and fruit growth.

Should You Put Something Underneath Watermelons As They Grow

I have never put anything under my watermelons and have never had a problem with them.

If you have had problems in the past with bugs or rot then put something underneath like brick or wood and not cardboard, straw, or newspaper that can stay wet and bugs can get through.

Checking the color of the “field spot” on the watermelon is a good way to know a watermelon is ripe. If it’s golden yellow and you can barely or can’t see strips in that spot the watermelon is ripe. That and the stem being dry and not “green” are the best two indicators in my book.

Growing Watermelons Vertically

Growing watermelons vertically on a trellis may not be the first thing that comes to mind when you think of growing watermelons but it is entirely possible and comes with some great benefits.

watermelon growing vertically
These watermelons are grown vertically and supported by baskets tied to horizontal bamboo poles. You don’t need to do anything as pretty and creative to support watermelons. An old shirt folded once and tied to the support like a hammock will do.

The biggest obstacle as you might have guessed is the weight of watermelons hanging from the vines. You need to pick a personal or icebox type variety that doesn’t grow over 10 lbs. or use stronger supports that you can adjust. To support 10 lb. or less watermelons you can use pantyhose or anything you can think of and secure the watermelon to the trellis.

Also, a watermelon plants tendrils are not strong enough to climb up a trellis so you need to use a plant tie to attach the vine to the trellis. This is an environmentally friendly garden tie and this is a good budget garden tie. Don’t get garden ties on a fishing line spool they tangle and are a mess.

The benefits of growing vertically is extra sunshine for the foliage and usually better yields. Watering goes directly onto the soil leaving foliage dry and with better air circulation. All this leads to a healthier plant less likely to succumb to rot or disease.

Watermelon Flowers & Pollination

Watermelons are monoecious and have male and female flowers on the same plant. The male flowers show up on the plant 7-10 days before the female flowers.

It is easy to tell the difference between a male and female flower because behind female flowers is a bulge that is the ovary that looks like a miniature watermelon and will grow into a watermelon once pollinated.

When the bulge behind the female flower grows to golf ball size you know it has been successfully pollinated. 30-35 days after this the watermelon will be mature and ready for harvest.

Here’s a couple of related articles

  1. Watermelon Flowers & Pollination – Everything You Need to Know
  2. How Long Does It Take to Grow Watermelon?

Are Watermelon Plants Annuals or Perennials?

Watermelon plants are annuals that will live out their life cycle, produce fruit and die. Even watermelon plants grown in areas with the right conditions year round need to be successively planted to get a continuous watermelon harvest.

There are plants known as egusi that grow in the Sahara that are perennials and may be the ancestor of the watermelon.There are two other plants that are also considered potential ancestors of the watermelon. Here you can check out the history of the watermelon.

Problems While Growing Watermelons

Temperature – A watermelon does well with air temperatures between 65-85 degrees. If temperatures are going to reach over 90 degrees for a few days during flowering and the beginning of fruit production you should do some things to prevent heat stress. Water more frequently during hot weather and put keep the watermelon plants shaded during the hottest hours of the day using bed sheets, sun umbrellas, or shade cloths.

Pollination – Watermelons are insect pollinated. You should hand pollinate if you live in an area with little insect activity, a balcony in a city for example, or have a week of bad weather, cold weather, below 65, or hot weather , above 85, or a week of rain and clouds insect activity will be lower. This is a simple process where you use a paint brush or other tool and swirl it around the inside of the male flower and then the female flower.

Pests & Disease – For pests in the garden use neem oil and manual eradication. Neem oil is an organic pesticide that comes from the oil pressed from neem seeds. It coats the foliage of the plant like a wax and makes it inedible for bugs.

Neem oil combined with aggressive manual eradication is the best way to get rid of pests on watermelon plants and most pest problems in the garden. Spray neem oil on the infested plants every two or 3 days.

To manually eradicate walk through the plants and squash the bugs or throw them in a bucket of soapy water making sure to check the bottom of the leaves for eggs.

Disease will look different than a nutrition deficiency because it will be more severe, more black and brown than yellow, and at first will likely be just a section of the garden.

Please comment below with any of your own thoughts and experiences on watermelon plant care and growing tips.

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