Pour watermelon juice into ice cube trays and freeze overnight.
Place 4 frozen ice cubes in a glass with a splash of lemonade and allow it to thaw slightly, enough that it becomes slushy and you can stir the lemonade into it.
Serve immediately garnished with lime wedges (optional) and a straw.
The amount of each ingredient you use will be dependent on how sweet your watermelon is. You want a combination of 2 TBS of liquid per 4 cups of watermelon and then sugar to add some sweetness. See recommendations below:
If the watermelon is average (not super sweet and not unsweet) – use 1 TBS lime juice, 1TBS lemonade, and 2 TBS sugar.
If the watermelon is on the sweet side – use 1 ½ TBS lime juice, ½ TBS lemonade, and 1 TBS sugar.
If the watermelon is not very sweet, use ½ TBS lime juice, 1 ½ TBS lemonade, and 2 TBS sugar.
Error on the side of the watermelon being average (per the notes above) and use 1 TBS lime juice, 1 TBS lemonade, and 2 TBS sugar if you can’t decide whether your watermelon is sweet or not.Store the frozen watermelon ice cubes in a freezer bag for up to six months. When you want to make a watermelon slushie, simply grab four of the ice cubes, add some lemonade, and enjoy!Prep this ahead of time by making the watermelon drink mixture and freezing the ice cubes overnight. Then to serve this for a party, just add the ice cubes to glasses with some lemonade a few minutes before serving. It’ll only take a few minutes to go from cubes to slushie and be the perfect summer drink!