Design front yard using black mulch & rock (river). ?? Desert theme.
That is quite an undertaking. The first thing I would do is clean up the base of the tree to expose more of the trunk, and weed out the bed. Black mulch and river rock doesn't really scream desert theme to me (just my opinion) but you could try to lay out a design that looks like a wagon wheel using the tree as the center hub and alternating between your other materials for the spokes. Suggest rocks for the spokes, mulch as the blank space between the spokes. If you have enough of the rock, use them all around the edge for the wheel portion as well. From the angle in this picture, you may be able to see the wagon wheel, from the door looking out, you may not get the same effect. Good luck and enjoy your project!
I agree that the first thing you should do is have the tree trimmed as well as cleaning up the base (cutting tree shoots, etc.) This in itself will make the house and yard much more presentable.
You've got a huge expanse that will be quite expensive to cover with mulch and rock. I think you should measure out the area and calculate how much of each material you need and the cost for that before you move forward with any design. (unless your budget is unlimited lol!)
I don't know your location but can you put in grass seed or sod for some of the area? Are garden beds doable in your growing zone? Personally, I would put in grass or other ground cover that you're able to walk on. Some beautiful perennial flowers in beds around the house itself. I'd reserve the mulch and rock for under the tree and around the garden beds.
Depending on where you live I would look into drought tolerant plants that will do well in the zone you live in and then mulch or small rocks around
Since I don't know where you live, I'm only going to suggest techniques. First, prune back the mulberry and see what you've got to work with on the ground. If nothing grows in that sandy area, you won't really need weed block, but it does hold things in place - just sayin'. To create your design lines, you can use a hose or spray paint sold especially for painting the ground. Since mulch will move, I'd suggest putting down some kind of edging to keep that in place. When you're laying the materials in, work from either one end to the other or from the center out. That way you won't keep tripping over your own work. (Rock will trip you.) Add some interesting focal points: an area of cactus or other plants, a stack of rocks, a metal sculpture or other things that say 'desert' to you. I would like to add that there's not much black on the ground in most deserts - mostly grays and tans, even some browns. Your design should have gentle curves and no straight lines. Draw it out a few times on paper to work your ideas into a final design - and you'll probably still tweek it as you work.
I would forgo the rock and mulch and put a wood deck that encircles the tree. Put a bench or two to enjoy the shade from the tree.You can border the outside perimeter with rock or mulch but not both as they will intermingle in time. You have a beautiful tree and property and I would highlight that.
When you use river rock mulch make sure you put down a weed barrier first. Same for the black mulch if it is a natural material. Otherwise the rocks will go down into the soil and it is almost impossible to ever remove it if you change your mind.
You could put a large circle of the river rock next to the tree and the black mulch on the outside in an undulation border with low plantings and a focal point like, for instance, a large rock or grouping of large rocks. Then repeat a variation of the focal point two other places but on a much smaller scale.
I agree with an earlier comment , that black mulch and river rock doesn't seem like desert landscaping... when I think of desert landscaping I think of light rock and low water tolerant plants , not necessarily cactus , but there are other bushes and flowering plants. If you really want to incorporate the black mulch and river rock , which can get expensive for the size area you are showing , maybe for a winding path through the area in black mulch and line it with the river rock .