Spinach loves cool weather and is frost tolerant. You can directly sow into the outside soil in spring when the soil can be worked on. Stop planting when the weather is warm. As described earlier Spinach germinates the best in cool weather.
Make sure that the soil is rich with organic matter and compost. Keep the balance between adding the organic matter to the soil as too much nitrogen can affect the taste of the Spinach when harvested.
You can harvest as soon as the leaves are big enough. You can even cut the entire plant from the root. This is the good option when you are approaching warm weather.