Here is what I suggest for northern tropical growers.
Over the years I have been trying to breed hardier easier to grow tropical plants. I live in a zone 6 which mean on average we get to 0F or -10F. One trick that I have found to be a cheap and easy way to raise your zone up 1 or more zones. First you have to know which plants can handle this treatment. I found it to be plants with bulbs tuberous or rhizome these plants have natural storage devices for energy and usually a natural dormant cycle. It seems that as long as the storage device tuber bulb or what have is not frozen it survives. By putting 4 to 6 inches of chopped up leaf compost on top of the crown of these plants I can raise my zone up to 7. Now if I have plants such as Musa basjoo or Ensete which have large trunks I can mulch them up 1 to 2 feet sometime adding un-open bags of leaves around the base of the plant filling in the center with leaf compost. This often protects part of the trunks and come spring I will have new foliage straight out of a trunk rather than the tubers producing a new shoot underground. This can usually add 3 months of growth to a plant with a shorter growing season.
Now for even more protection I can use my old greenhouse plastic over top of these mulched beds and keep out zone 8 and 9 plants with bulbs tubers or rhizomes. The plastic should be secured down tight so that high winds do not take off with it. When spring the plastic will start to heats up the soil fast and the plants are usually up a few months early many with well established roots.
Another great things about this is in the spring the extra leaves are removed so plants do not suffocate usually anything over 8 inches should be moved off of the plants. I usually just take a leaf blower or a pitch fork and move any large layers off that maybe to much. The rest of the leaves are left on. I then add nitrogen and some lime on top of the leaves they rot quickly and start to lay more flat after Aprils rains. This mat of leaves keeps out most would be weeds that would regularly take over. The leaves decompose into very rich soil and over time my beds become full of dark rich soil which the plants really love. I also found that the mulched up leaves help retain moisture to the roots. Their is not enough that can be said about using this technique for norther tropical plant growers. Many people have asked about installing a greenhouse for storing their Cannas Colocasias Bananas and so forth. I tell them that if they do this with the plastic it is cheaper and easier than any greenhouse and unless the plant is extremely sensitive it will almost always works better than any greenhouse.
So if you want to leave your tropicals out get better soil reduce weeds have your plants months ahead of everyone easel's then you should look into this. It has worked great for me for the last 15 years.
Here is how it works.
In zone 6 our frost line is 4 inches which means 4 inches of leaves should put your tubers and rhizomes blow the frost line. Composted leaves are shredded so that they have air between them but can also rot. The air helps insulate the ground while the leaves start to compost they also give off heat from the microbes eating the leaves. Adding the plastic causes the suns raise during the day to thaw out the soil and raise the temperature of the ground under neither. When night comes and the temperature drops the trapped heat is under the leaves and the plastic and can take all night to cool down.
It seems to work best when the plants are together in one large bed that way the whole area can stay warm rather than small spots. I can before and after pics of this entire process. The leaves are given to us sense we post a large sign that reads LEAVES WANTED. Amazing how many people are always looking to get rid of leaves in the fall. I usually have so much I just store them in huge piles on the back acre to rot and sell as compost.
