Winter growing means different things in different places.  In mild climates, some seed can be planted in fall and leaves can be harvested throughout the winter.  In harsher, colder climates, some seeds can be planted in either early fall so the roots have time to get established or in the cooler soils of late March or early April, for early spring growth.  One key thing about winter growing is the light change.  The sun actually shifts and hits thee earth at a different angle.  It's important to plant before November 15th or after February 15th, especially in northern climates.

Growing in a greenhouse or high tunnel will help extend your season, and so will using "row cover".  Row cover is a spun-bond polyester fabric that you can drape over your plants to increase the temperature by a few degrees.  Using two layers extends its protection even more (but lest in less sunlight).

Red Russian Kale:  kale is a hardy biennial that will overwinter in mild climates, and gets sweeter afttter a frost.  Sow fall plantings tow months before first expected frost date for full sized leaves, or up until the frost date for baby leaves.

Yankee Hardy Lettuce Mix:  Sow in fall or spring.  Lettuce is a cool season annual, and will geerminate at temperatures as low as 40 degrees.  Seeds will take longer to germinate and grow more slowly in cooler conditions.

Sylvetta Wild Arugula:  Arugula is a hardy annual that is cold tolerant.  Fall planted arugula will overwinter in mild climates for an early spring harvest.

Giant Winter Spinach:  Spinach is a cool season hardy annual.  Over-wintered spinach is best started in late summer and harvested in late winter when days begin getting longer.

Pink Beauty Radish:  Radishes are hardy annuals and are better adapted to the cooler temperatures and shorter days of spring and fall.  Plant as soon as the soil can be worked in the spring, or in the early fall for a late fall harvest.