Written by Spirekassen 30 Mar 2023 08:36

Saying goodbye to the winter cultivation


The 1st of March is a special day for many people. It is on this day we mark the end of winter and the beginning of spring.  

It is not quite like that though, astronomically speaking. We, on the northern hemisphere, first enter spring, the 20th of March, when we hit spring equinox. It is time to harvest and remove the last of your winter vegetables and leafy greens. Everyone with a greenhouse knows that spring IS HERE! With the arrival of spring, we say goodbye to winter cultivation in the greenhouse.  


The flowers are taking over

Here at Spirekassen, we put tulips and daffodils in our raised beds this fall. From the beginning of March, we can start to pluck tulips in the greenhouse. We also grow French anemones in our greenhouse, where they bloom significantly earlier than outdoors, but they quickly become too hot in a warm spring greenhouse and wither quickly as well.  

Spring is coming

The days in the greenhouse are becoming warmer and warmer. You can easily experience 20-30°C at certain times a day when the sun is shining. When the sun has set in the night, however, there is still the possibility of frost in the greenhouse. During springtime, the greenhouse is marked with high temperature variations. If you don’t already have a Juliana window opener, it is a good idea to get one. They control and regulate the temperature variations and make sure it won't get too hot on sunny spring days. 


Cabbage plant develops seeds  

If you have been growing cabbage in your greenhouse all winter, you might experience that the plants are bolting now. That means the plants start to form seeds. Hereafter, the plants will die. This is a natural reaction of most cabbage plants. During a long and cold winter, the plants have been focused on surviving. When it gets warmer, it is relevant for the plants to form and mature seeds. In nature, the mature seeds with fall to the ground and start to sprout all over again. The plant's life cycle has been completed. That is why, it is difficult to move plants from the winter into the kitchen garden in spring, to let them continue growing. Some cabbage types, such as swede, will not bolt as easily after a cold winter period and can be moved into the kitchen garden and finish growing with a little luck.

Cabbage tips  

If you want to utilize the greenhouse for pre-cultivation of your cabbage for your future kitchen garden, pre-germinate fresh seeds from the end of March in the greenhouse. Plant the small plants in your kitchen garden in the end of April.  


Sowing lettuce 

Before the winter is completely over, sow a row of lettuce in the greenhouse. Try to sow your lettuce seeds in a jar or pot if you don’t have a raised bed. Lettuce and salad do not thrive in the heat. Therefore, March is the last chance to grow lettuce in the greenhouse. Remember to use seeds from a lettuce type, that is for increasing light, also called ‘summer lettuce’’.  

The boring job  

Cleaning is a spring job most people don’t enjoy. The greenhouse needs a thorough wash. Both glass and profiles need to be washed. It is not necessary to use soap. Just use regular clean water. If you are interested, you can read my previous article about greenhouse cleaning. Even though the article was written in autumn, the principle is the same.


Soil improvers  

Before the start of the summer half-year, it is a good idea to add soil improver to the existing soil, if you have beds in the greenhouse. If you have the opportunity to obtain organic fertilizer or compost, it is time to add it now. Alternatively, you can also add fertilizer in pill form to your potting soil.  

Spring starts now.