Hardwood cuttings are made from the budded branches of last years growth. So the new growth from this growing season is what you'll make cuttings from next year. You'll see the buds, they're very easy to see.
Cut lengths, the longer the better, but when planted 2/3rds go into the ground. I carry a pruning shears with me when I plant so I can cut off tops that are too long. The 2/3rd rule is so that there are enough roots to support new growth, and in sandy soil cuttings need to find water. When I plant I use a length or rebar to make a pilot hole and drop the cutting in the hole.
I've grown cuttings without weed mats, but weed mats are really a must. Anything that holds moisture and blocks weeds will work. I Initially used cardboard, house wrap, and lumber wrap. Then I used black plastic, the type sold at farm stores for covering piles of foliage, discovered that black plastic worked wonders.
Then I discovered Lumite, which is made for planting trees. Initially I rolled out lengths of Lumite, but then I needed to thin my cutting to a 5-6 foot spacing after one year and eventually I thinned to 15 feet, so a 50 foot stretch of Lumite only had three trees in it..... seemed like an awful waste, so now I cut 6' x 6' squares. 6' x 6' will seem too big, but it'll look too small in a year or two. The weed mat does much more than control weeds, it's a moisture barrier. Water is always evaporating from the ground, even in a desert. That water will be trapped under black plastic and Lumite, so the cutting always have water, and growth explodes.
Bill commented about my deer not stepping on black plastic. That's because my deer are pursued by Ozark rednecks year round, and are shell shocked. My deer won't eat out of my corn feeder either. Now my deer have grown accustomed to black plastic and Lumite so, if you have many deer you'll need to buy cheap rigid mesh tubes:
http://www.benmeadows.com/rigid-seedling-protector-tubes_36811405/?searchterm=Rigid+mesh+tubes
All cuttings can grow in black plastic, and everything grows in Lumite, because Lumite breathes. When researching the tree you're planting, check the USDA Profile and Characteristics. It the plant has low anaerobic tolerance, then plastic can smother the tree and deprive it of oxygen, however, all cuttings can be planted in black plastic, it was only when I put plack plastic around trees like pin and some oaks that I experienced problems. Trees that can be submerged in water are anaerobic tolerant and black plastic will work fine for them.
After a cutting had grown 4-5 feet an X needs to be cut in the plastic or Lumite so the trunk has room to grow. The following year the X will need to be enlarged to the size the trunk will grow in 5-7 years, at which time the Lumite or plastic should biodegrade.
