Cultivating Spinach in Winter
The autumn is showing all its force in October. The nights are getting longer, it is getting colder and the first night frost is just around the corner. Those of us, who have a greenhouse are lucky, because we can expand the growing season into autumn and winter.
If you haven’t already tried winter cultivation in your greenhouse, you should try it. Winter cultivation simply means to keep cultivating plants in autumn and winter. However, keep in mind, that everything grows slower, which affects the harvest you can expect, and you also must grow other plants and varieties than in summer.
A plant especially suited for winter cultivation is spinach. If you have cultivated spinach before, you have probably experienced, that the plant can quickly bolt and produce seeds, if the summer is too hot. During the summer heat, the development of the plant happens so quickly, that it can be difficult to harvest all the leaves in time.
This is why it is clever to cultivate spinach in autumn. The temperature will have worn off a little bit, but there will still be enough warm days in the greenhouse to benefit your plants.
Learn More About Spinach
Spinach (Spinacia oleracea) is an annual leaf vegetable. It is related to beetroot and leaf beet. Spinach is an old culture plant, that has already been cultivated in Persia over 2000 years ago. The original uncultivated spinach plant is native to Southwest Asia. Spinach contains oxalic acid, just like rhubarb. When you eat fresh spinach leaves, you will get a sense of roughness on your teeth, or you might experience a stomach-ache, if you eat a lot of raw spinach. It is best to cook the spinach with products that are high in calcium, like dairy products. They neutralise the oxalic acid.
Spinach is a Long-day Plant
Spinach is a light sensitive plant, which means that the combination of day and night length influences the seed formation. A warm summer or/and a period with cold weather, followed by heat will make the spinach bolt. When spinach bolts, the plant will produce seeds and thereafter wither and die.
Spinach is originally a long-day plant. That means, the plant needs a night, that is shorter than the day to be able to grow and produce seeds. During summer, these conditions are fulfilled in the North, but the summer heat can almost speed up the process too much. The spinach plant can simply wither down before we have time to harvest the leaves. Luckily, there are spinach variants adapted for summer, such as the spinach ‘Early Giant Leaf’.
In the same way, there are variants developed for long nights and short days and therefore suitable for autumn and winter, such as the spinach ‘Winter Giant’. A spinach variant adapted for autumn in combination with the October climate in the greenhouse are offering the perfect conditions to cultivate spinach at this time of year.
It is not a good idea to cultivate spinach in the greenhouse in September. The climate in the greenhouse can still get too hot and might be too fluctuating.
Different Options for Sowing Spinach in the Greenhouse
- You can easily recycle the soil from your summer plants for cultivating spinach in winter, as winter cultivation does not require a nutrient rich soil.
- If you have fixed beds, you can sow the spinach in rows, as you would do in your kitchen garden.
- Another option is for the spinach to take over the space in the self-watering boxes. This way, the spinach will replace tomatoes, cucumber, and chilli plants. You do not need to change the grow bag.
- It is also possible to broadcast (*) spinach in seed trays.
- A final option is to broadcast (*) in smaller pots, that can be taken straight into the kitchen when needed.
Fun Facts about Light Sensitive Plants
Some plants first flower when the night is long, and the day is short. Other plants do exactly the opposite. A third group of plans is not affected by the day or night length at all. If the plant is native to areas around the equator, the plant is able to measure the days length within minutes. Plants that are native further away from the equator, for example the polar circle, are not as particular.
The terms short-day plants, long-days plants, and day-neutral plants are actually a little misleading. It is always the length of the night that is important to the plants. The measuring happens in a plant protein called phytochrome. Phytochrome is best described as a pigmentation system in plants and plays a central role in sprouting, plant growth, flowering and seeding.
(*) Broadcast seeding means to sow seeds in a larger area, in this case it might be a big seed tray, by spreading out the seeds just like sprinkling salt on food.
Christine Wiemann is a greenhouse grower and an agricultural technician and owner of the seed company Spirekassen. Christine is an author of several books about lifestyle, garden life and plant cultivation. Today she writes blogs and shares her knowledge and passion for greenhouses. Christine is a greenhouse expert and an ambassador for Juliana Drivhuse.Get to know Spirekassen
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