Although many flowers like to be started when mild weather arrives, there are some that prefer to have some cold spells before they germinate. In nature, these are typically seeds from perennials that flower early in the season and prefer cool growing conditions such as the 'Brilliant Red' Oriental poppies and 'Summer Skies' delphiniums. The seed reaches the ground and is subject to alternating mild and cold spells, plus frequent rain or snow. Without these natural rhythms of winter, the seeds are reluctant to germinate. Seeds from hardy annuals such as 'Blue Boy' cornflowers can also be sown in winter to get a good start early in spring. Traditionally all these seeds were sown in a cold frame, but smaller containers work just as effectively and are far more economical.
There are two ways to sow seeds in winter; either directly sow the seed on the snow or ground, or sow in a container that gives some protection from animals. Popular containers include gallon milk jugs, plastic fruit juice containers and plastic food containers. Germination rates for direct sown seeds will be lower than those sown in containers where animals cannot eat the seeds and excess moisture does not dislodge them. However those that do survive will not need to be transplanted and can produce sturdy plants from the time they first germinate.
Make sure that your container is clean and punch a few holes in the bottom for drainage and one or two on the top for ventilation on sunny spring days. If you are using a milk jug, or other large container, make a cut three quarters of the way around the middle of the container so that the top can be levered backwards to ventilate the container, and closed when the seeds need protection. Fill the lower part of the container with damp potting mix and sow your seeds. Replace the lid and seal with waterproof tape or duct tape. Place the container outside and wait for spring. The seeds will germinate when the weather is just warm enough and they will not suffer from too little light which is a common problem with seeds sown indoors.
When the seedlings are large enough to handle, they can be placed into your flower border to continue growing.
Most winter sown seeds will germinate early and will produce healthy plants that flower slightly earlier than those which are sown indoors and need to be hardened off before mature growth starts.