When to start sowing seeds, I think we are all desperate to start gardening in the spring.
As a nurseryman, I believe most gardeners start too soon. Using the data from our nursery climate computer, I calculated the total sunlight for all of January is only equal to one sunny day in July. What does this mean? Well if you wait, and sow your seeds later, they will soon catch up. The sunlight levels in March and April are better (more than 12hrs per day) and the average daily temperature is higher, so your seedlings will grow stronger and faster.
If you still want to start early, you will also need to find a way to balance temperature and light. Light without heat won’t work and heat without good light will just produce thin straggly plants.
Side view of tomatoes left natural right extra light and heat
Tomato seedling on the left germinated then moved into glasshouse with average temperature 16 C on the right given 16 hrs of artificial light and average temperature of 18
These Tomato seedlings show just the effect of heat, left hand side on heated bench, right hand side unheated bench. The left-hand side would be 4 or 5 degrees warmer than the right hand side
Top view of just extra heat the plants are bigger and more advanced, both trays have had the same amount of natural light.
