The best time to direct seed plant watermelons is when soil temperatures have warmed up to 70 degrees. Use a soil thermometer. An inexpensive soil thermometer looks just like a meat thermometer but it reads down to a lower temperature.
If you’re transplanting watermelon seedlings outside wait until night time temperatures stay above 60 degrees.
To get a good average soil temperature take the soil temperature between 9-11 AM when the soil has warmed some from the night chill but isn’t inflated by the afternoon sun.
Stick the thermometer all the way into the ground and wait 5 minutes. If it’s 70 or above you’re good to go to plant watermelons.
To learn how long it takes for watermelons seeds to sprout and more check out “How Long Does It Take to Grow Watermelon?“
When Are Watermelons In Season?
Watermelons are in season from May through August. During this time the majority of watermelons come from Florida, California, Georgia, Arizona, and Indiana. In the winter months most watermelons come from Mexico.
This cool graphic shows watermelon production by month and the major producers during those times.
Can I Plant Seeds From a Watermelon I Got at the Store?
You can plant seeds from a watermelon you bought at the store and they will most likely grow into a watermelon plant.
The seeds from a seeded watermelon that reached maturity are a good uniform size and a dark black or brown color. The white “seeds” in a seedless watermelon are just the shells or hulls of seeds where seeds were supposed to form.
Most commercial watermelons are grown from hybrid seeds. The seeds from these hybrid watermelons will produce a watermelon with characteristics that could be like either of the parent varieties or a mix of the two like the hybrid you got the seeds from.
If you were shopping in a specialty store or the organic section you may have gotten an heirloom variety of watermelon.
Both parent plants of an heirloom variety are the same variety watermelon and the seeds from this watermelon will produce watermelons that are identical to the one the seeds came from.
What Month to Plant Watermelon
What month to plant watermelon depends on where you are located. If you live in south Florida planting watermelon from January through March is a good idea but if you live in Michigan it’s a bad idea. Plant watermelon when soil temperatures have warmed up to 70 degrees and night time temperatures stay above 60 degrees.
Saving Watermelon Seeds to Grow Next Year
You need to harvest seeds from a mature and ripe watermelon to get mature seeds. Extract the seeds from the mature watermelon and rinse them off in a strainer.
Next soak them in soapy water or a 10% bleach mixture for 10 minutes to make sure there is no sugar left on the outside of the seeds that can cause mold growth.
Next rinse the seeds off and lay them in a tray on paper towels and allow them to air dry for a few days. Store the seeds in a cool dark area. A refrigerator is a good place to store the seeds.
Soak Watermelon Seeds Before Planting
It is not necessary to soak watermelon seeds before planting. The point of soaking the seeds is to increase germination rates. I’ve never had a problem with low germination rates with watermelon seeds.
I think this may make sense if you were using old seeds that you weren’t sure of their viability. If I was planting old seeds I would try and sprout the seeds in paper towels and a ziploc bag to check the viability or just stick them in the ground and see how they do.
Other methods of increasing germination rates include “seed scarification”. This is done by using pliers to open the seed a little and/or sandpaper to thin the walls of seeds to make it easier for water and air to penetrate the seed.
Some people call for soaking seeds in milk. The theory with that is you’re adding nutrients for the seed to use while sprouting.
Is It Too Late to Plant Watermelon?
The way to know if you still have time to plant watermelons this season is to know how long the variety you’re growing takes to produce mature watermelons. An average is 90 days for a watermelon to reach maturity after sprouting.
Pull up the average temperatures by month in your area. You need more than 90 frost free days to successfully grow watermelons and for them to grow well 90 days where the average night time temperature stays above 60 degrees.
Although you can get a head start on the season by starting watermelons indoors if you’re late on planting that doesn’t help much.
Starting Watermelon Plants Indoors
Fill starter pots with a seed starting mix or potting soil. Seed starting mixes are very light and loose mixes with a texture that allows easy root growth. Potting soils are similar. Using dirt from the garden can do but is generally frowned upon because of possible pests or disease in the soil.
After your starter trays are filled up drop a watermelon seed onto the top of each pot. Take a pencil and push the seeds down into the soil about 1/4″. Cover with some dirt on top and gently water the pot from the bottom.
To do this fill a flat tray with about a 1/4″ of water and set your starter pots in the water. To check on the pots feel the top of the soil in the starter trays every 15 minutes or so. When the top of the soil feels moist it’s watered all the way through and you can dump out the rest of the water in the tray.
Water when the soil feels dry. Lifting a starter tray and feeling its weight is a good way to know when to water also. Use water that’s at least room temperature. If you’re using a grow light or a heating pad expect the soil to dry out sooner.
Keep the starter tray in a warm area that stays between 70 and 90 degrees. After the seeds sprout the plants need light. Many south facing windows or one large south facing window can work but one small south facing window may not be enough.
If the small sprouted plants don’t get enough light the stem will become spindly and the plant will fall over on itself.
The best scenario is to set up a grow light and in this way get some serious vegetative growth before moving plants outdoors.
A T-5 Fluorescent like this is not the most thrifty option but it is great for vegetative growth and can be used for a plants whole life cycle to flower and fruit but is not ideal for this. This T-5 light measures 2×4′ and will cover an area of 4×4′ very well and an area of 4’x6′ well.
At the ends of the 4 feet fixture the light stops abruptly but it puts light off to the sides. In my experience bulbs will last for close to 2 years with constant use although in the second year they will operate at around 75%. This T-5 fixture has 8 bulbs and two power switches that allows you to operate 4 bulbs independently.
An alternative to this is a high quality LED light. The initial buy price is over 3x that of the T-5 but it will use about 1/3 of the electricity. It will cover a similar area and is better if you want to flower and fruit a plant indoors. This brand Lush Lighting I know to be quality.
Transplanting Watermelon Plants Outdoors
Harden off seedling watermelon plants gradually over a 7-10 day period. Start by placing the seedlings outside during non peak hours of sunlight and sheltered from the wind. Progress to leaving them outside for an entire day.
Always remember to bring the seedlings back in at night during this process. You can start to strengthen the seedlings while indoors by placing a fan on them.
Please comment below on anything above!