No, you don't have to bury it. There are many ways to build these. I built really high raised beds using old lumber as walls. One bed is raised well over a foot, another, an earlier half-ass attempt, is about 6 inches. Then I just threw in some old rotting wood and piled soil on top. In spots you hit would just an inch or two under the soil, in others the soil is quite deep. Given the heat and mosquitoes at the time, it was a rushed effort.

I've recently built a new bed nearly two feet in height. I'm using them to grow leafy greens mostly, with some peppers going, some moringa of course. I need to order some seeds -- eggplant, tomato, various greens, peppers, etc. You're lucky to be able to buy really high quality seeds in Taiwan (Known-you).

Another technique to look into is keyhole gardening. (Google simply 'keyhole garden'). Very interesting. I haven't tried that yet and probably won't in the near future, but I have been developing another idea -- bamboo watering stakes.

Very simple really. Cut some bamboo, leaving a knob at one end so it can hold water, the other end being open obviously.

I have very sandy soil. Water runs right through it. I need ways to hold water in the soil. Hugelkultur works great, but I'm just playing around with this other idea. I used bamboo stakes to build my raised gardens, and noticed how well they hold water. What if I could find a way to have that water released into the soil very slowly? I tried drilling tiny tiny holes, but the water ran right through. I thought the bamboo would swell and hold it, but so far no luck.

Next I'll try drilling tiny holes, or perhaps scarring the outside of the bamboo, then putting a heavy paper inside the bamboo around the inside edge, rolled up.

Another option is to simply fill the hollow bamboo with compost, perhaps packed tightly, hence the connection to keyhole gardens. A compost-filled bamboo watering stake would be like a miniature keyhole garden 'area'. A bed of vegetables would have many stakes, perhaps spaced 1 to 2 feet apart.

Yet another option is to drill larger holes hear the top of the bamboo so that they (the holes) sit about 1 inch under ground once I drive the pole into the ground. Then, the bamboo will hold water up to those holes. Theoretically, roots would then find those holes and the water reservoir, making this a type of hydroponics.

I will prevail with my bamboo watering stakes!