I have about 140 linear feet of hugelkultur beds here on my Central Texas farm. They are about a year old. This being a hot, dry region in summer, I elected to trench instead of building up. The first trench I dug by hand and it was very hard going in the rocky, limestone ground in my back yard. So I hired a friend and a mini-excavator to dig the remaining trenches. They are four feet deep and four feet wide. Two of the three trenches were filled with partly rotten wood, leaves and twigs from my farm, and the third trench I filled with spoiled hay and manure from my barnyard (it's an experiment). The three trenches were then topped off with good soil before planting.
Hugelkultur works, no doubt about it. But some patience is required. For example, you should expect a nitrogen deficiency for the first year or so as the carbon in the wood, leaves and twigs breaks down. This can be overcome by adding a nitrogen fertilizer as you plant. The decaying wood will gradually break down, building thick, rich soil. You can expect some subsidence and you'll need to add organic matter each year to compensate.
Wood contains and absorbs moisture and the idea is that the plant roots can tap the moisture in the wood over time. When you go the trench route, you are creating what amounts to a sponge. When it rains the trench will absorb water and release it to the plant roots on demand.
You need to be careful what kind of rotting wood you put into your hugelkultur beds. Certain species are allelopathic (they suppress competing species) and you want to avoid that. For example, don't use walnut, pine or related species. Oak, ash, pecan and similar wood is fine. I would avoid sawdust. Here we have a lot of ashe juniper, and it's not suitable. Do a bit of on-line research about trees in your area before you begin to dig or mound.
A well crafted hugelkultur bed should require little fertilizer once established and it should be good for many years of service. Last spring I planted certified seed potatoes and was very pleased with the results. Due to time constraints this fall I planted a cover crop (Austrian field peas) to fix nitrogen in the soil. The next planting will be in the spring. Our best gardening season here is fall and winter, and most of my vegetables are in raised beds and my keyhole garden. The hugelkultur beds will lie fallow until spring. Also, I want to add another layer of topsoil before I plant again, and that will just have to wait.
Anyone seriously interested in hugelkultur should also check out keyhole gardens. You'll find good information on YouTube. Look at the excellent series of short how-to-build-one videos by Dr. Deb Tolman. Dr. Deb lives in the next county (she moved here from Portland) and she has really gotten folks around here fired up about keyhole gardens. In her rural county of perhaps 18,000 people, there are now more than 60 keyhole gardens. In my much more populous county they are also starting to catch on. That's because they really work in our climate here. Check it out, and good luck.