I have found that if you want to harvest veggies all winter long you have to start the seeds in the fall. There isn't enough light during the day to get much growth. You need longer days with stronger sunlight than what December brings. So, you could plant seeds for something like carrots that take a long time to sprout anyway and just let them do what they will or you could start some seeds indoors and then transplant them out in the cold frame after you harden them off a bit. It's always a crap shoot - if you start stuff too early and we have a mild fall you'll get too much growth and lettuce and stuff will bolt after one mild day (it seems) or you start them late and it stays cold and cloudy and nothing grows til Spring. If you have the empty space I say go ahead and plant something but don't expect a lot of winter growth.

You should be able to plant all winter in your location. The soil will stay a lot warmer than the air, and roots continue to develop and establish much of the winter. It's quite incorrect to think that the roots of woody trees and shrubs (or much of anything) stop growing in the fall and winter. Even deciduous trees that are fully dormant should be planted in the fall/winter in your climate. The roots will grow! You probably have several months of establishment time ahead of you, until the soil gets cold enough at root level to slow down growth. By that time, unless your trees are extremely large, they should be fully established. As a matter of fact, fall is THE ideal time for planting in warm climates. The top growth slows down so that the plant can concentrate on root development. It's a good thing. It used to be common knowledge; I wonder why it isn't anymore. Your trees should be well established by the time hot temperatures roll around in the spring of next year. The last thing you want your new trees to experience is bud break, new growth, and hot temperatures on a root system that isn't developed yet. Be sure to follow proper planting methods...dig the hole no deeper than is needed for the rootball to sit at soil grade or higher....but two to three times wider. Do NOT add soil amendments of any kind into the hole or mix with the backfill. Use the native soil. Mulch with a 2 to 3 inch layer of something organic like pine straw, bark chips, etc. but do not pile the mulch up against the trunk. Be sure to keep the root ball watered and moist. Fall is the time for planting in all warmer climates. Actually, this is true for anyplace where the soil doesn't freeze solid. Don't trust information you get from HomeDepot. Once year, I over heard a clerk telling a customer that she could plant the cut Christmas tree she had just purchased in the ground after the holidays. A CUT Fraser Fir! Lordy.

I found this on Piviones Riviere's website. WHAT IS THE BEST PERIOD TO PLANT ? How do you plant a peony? To obtain the best results in peony cultivation, pay very special attention to the planting process. *Planting bare roots should be done between September and mid-March. *It is better to plant peonies in the autumn so that the root system can grow before the leaves come out. *Planting can be done during the winter period even with frost during the night as long as it disappears during the daytime. *After March, due to the growing of leaves and vegetation, it is not recommended to plant bare root peonies. *If you want to plant later, we offer cultivated plants in containers that you can buy either from our nursery or at the flower shows we go to. *Tip : In case of frost when you receive our plants, place the parcel in a cool area  a cellar or a garage - and open the parcel. The individually packed plants can remain for a month in their packaging without any harm.

If you have any deciduous trees around your house I think you can let them be your guide, when most of them have started leafing out from their leaf buds its probably OK to plant. Most years I don't think you have to worry about frost after March first, but I do remember one year when it was bitterly cold in March. For myself my clay soil is the determining factor. I always want to do a final rototilling to try to kill any weeds or bermuda grass that is growing where I plan to plant, and with clay the amount of moisture in the soil is very important, too wet and you have a sticky mess that clumps right back down, too dry and the rototiller blades just bounce off it and I have to get my 66 pound electric jackhammer and 14 pound clay spade for a total of 80 pounds to lug around to dig my planting holes. I also live near the bottom of the north west side of a hill so my yard is usually three degrees colder than the official weather report as the cold air pools in my yard, plus sunrise comes later because of trees above blocking the light from the east.