December Zone 7/8
Maples, Pine - white, Spruce, Sweetgum.
Fir, Pines, Spruce.
Fertilizing the following bonsai can be beneficial over the winter by suing a fertilizer containing a very small amount of nitrogen such as cottonseed meal, composted cow manure or diluted fish emulsion. Single superphosphate is highly recommended at this time of year since it does not contain any nitrogen. The concept in using fertilize at this time of year is to maintain a supply of nutrients for root and trunk development without start up of top growth which would be easily damaged or killed by the onset of cold temperatures. A teaspoon of singer superphosphate for an average-size bonsai should be sufficient; 1/4 to 1/2 teaspoon for mame bonsai. Larger bonsai will require, but do be cautious. Less is better. If you are in doubt, don't fertilize until next spring. Apple, Apricot, Azalea, Bamboo, Camellia, Cedar, Cherry, Citrus, Cotoneaster, Crabapple, Cryptomeria, Chamaecyparis - Hinoki, Cypress, Hemlock, Holly - deciduous, Juniper, Mountain Laurel, Peach, Pear, Pines, Plum, Podacarpus, Pomegranate, Privet, Pyracantha, Sasanqua, Spruce, Tamarix, Wisteria, Yew, Zelkova.
This is the least active month of the year for bonsai enthusiasts. You still have to check your trees for proper soil moisture. If necessary to water, do so during the warm part of the day when the soil is not frozen.You should make certain that all conifers and other evergreen bonsai get sufficient light so their leaves maintain a high chlorophyll level for resistance to pests and disease. Do not transplant this month. You can collect native plant material this month as long as the ground is not frozen. Most deciduous and evergreen trees will be dormant this month.  
Be alert to sudden weather changes. In the event of severe weather, be certain to give your bonsai added protection. Use additional mulch or place the bonsai in a cold frame until the severe weather subsides. Cold winds cause more injury than intense cold. If cold, windy days are in the forecast, you can use a simple wind-break to protect your bonsai or you can put them on the side of a structure away from the wind. You can also store your bonsai temporarily inside a garage or on a carport that does have some wind protection. If stored in a garage, remember to move your bonsai outdoors when the windy days are over. Wind protection is advised because the small branches of bonsai can be quickly dehydrated by cold winds, causing them to die and spoiling the design of the bonsai. Be on the safe side: water thoroughly on warm days if necessary and provide protection against cold winds during winter.