I put both foil layers on tightly. Main danger here is rain getting in and rotting the air layer so it has to be put on in a way that keeps the water out. Also try to put the foil on so the seam is on the bottom of the branch. Air layers put on during the active growing season are going to grow and do a lot better than ones put on during winter, especially outside of the tropics. Another very important factor is air layering branches that are in the full sun. Branches that don’t get sun will not produce roots. Ref: Oscar – Hawaii
Choice of wrapping for air layers depends on climate and personal preference. In the tropics I find that transparent wrap is not so good because if the sun hits it can bake the roots. I like to use two layers of aluminium foil, very easy to apply and no ties necessary. The reason I use two layers of foil is I found if I use only one layer sometimes the birds will peck a hole, but no problem with two. I don’t use any tape or any other tie. Just counter twist the foil on top and bottom. Some birds are definitely more bothersome than others. We don’t have crows here, which I remember do seem to get into everything. Only 3 main types of birds here: mynah, cardinals, and japanese white eye. Another option if you can’t get foil is to use one layer transparent plastic and another layer opaque, or if you can get very thick poly just use one layer opaque. Sapodilla can be grafted when about 30cms or more, but is easiest to graft when they are almost pencil thickness. Chikoo is the Indian name for chico (probably a transliteration), or sapodilla. It is possible to air layer them, but they take a very long time, up to one year, and have low rate of success. Ref: Oscar – Hawaii
I don’t have experience with longans, but this is what I do with hard to root species: – Make a cut all around and strip the bark and put little bit of powdered rooting hormone on the cut. – Wrap in sphagnum that was soaked and then squeezed. – Wrap in translucent plastic and tie on top and bottom. – Wrap the whole thing in black plastic or foil so the roots won’t be bothered by light. – Check if the roots are growing by unwrapping the outer layer (black plastic or foil) only. I do this on the upper branches only because they are more into growing and I first thin some branches around so the nutrients relay flow where they are needed. Even if this fails then I’ll try to grow a strong low branch and bend it into soil and out, and wound it where its going to be under the soil. Stake it to the ground or put a rock over it (and soil over the rock so it won’t heat up from sun too much. Ref: Vladimir – Hawaii
Citrus info from the Philippines. Marcotted trees tend to remain dwarf but weakly anchored, but it depends on the type of cultivar. For example, the marcotted rough lemons and lisbon lemons could develop extensive root system as strong as grafted trees. This I know because I marcotted and grafted them and they performed the same, but not true with mandarins and oranges, the marcotted ones are poorly anchored. With Calamansi, the marcotted ones are not as good as the grafted ones, but they remain smaller. If smaller trees are good for you in wind-sheltered areas, marcotted trees could suit your needs. If you want bigger trees that are well anchored, marcotted trees are not generally for you. One big advantage of marcotted citrus trees is that they bear quality fruits much earlier than grafted ones. Those citruses grafted unto seedling rootstocks would develop quality fruits 3 to 7 years after planting. They could produce fruits right away, but the quality won’t be as good until the tree reaches proper size. The marcotted trees will have good quality fruits right away. This is because with grafted trees, some of the juvenility in the rootstock is passed on to the grafted cultivar. If the rootstock is very old, like a mature tree, then you get quality fruits right away, but if the rootstock is a young seedling, expect 3 years at the fastest for a nice quality fruits. Ref: Joe Real