Growing from Seeds | 'Planting' seeds to grow the first seedlings & Selecting 'soil' medium: To get started growing dragon fruit cactus from seeds the first step is to choose a 'soil' medium which will meet the new dragon fruit plants growing needs for the seeds as they sprout and form the first small seedlings. The term 'soil' and 'planting' are kind of approximations here, but we'll use them anyway as far as getting dragon fruit seeds started growing. You aren't so much as planting the dragon fruit seeds as just giving the seeds the signal to grow to seedlings which you will then harvest for repotting or direct planting of the dragon fruit seedlings.
So, your aim in growing from the actual dragon fruit seeds is to actually grow seedlings, which you will then plant - so you are not sowing any dragon fruit seeds where the cactus plants will grow to maturity. Therefore, the 'soil' medium you want is really a soil for simply sprouting the seeds and not growing the cactus plant. This means that you want an exceptionally loose soil medium which will allow you to plant the seeds as close together as possible and let you easily separate the seedlings from one another as the seeds sprout and the seedlings put down roots.