Asparagus is generally grown in the open ground, and let me start by saying that it grows easiest there. But if you don't have space for asparagus in the open ground, or if you're in heavy clay, for example, which asparagus doesn't like, growing it in a pot or container can be an option for growing your own asparagus.
Asparagus is a perennial plant that returns every year. Their growth is somewhat comparable to rhubarb. You can harvest the foliage every year until the longest day (June 21st), after which you can no longer harvest from the plant. The foliage that grows after the longest day is important because the plant draws energy from it and stores it in its roots. This gives the root sufficient energy to survive the winter and produce abundant asparagus again in spring. As perennials, asparagus and rhubarb can therefore remain in the same spot in your garden for a long time. Asparagus can produce well for up to 20 years with proper care. However, because a lot of energy needs to be stored in the root, it also needs sufficient space to grow well.
What kind of pot or container do I need?
In the open ground, the asparagus plant can grow unhindered, but this is not the case in a pot or container. To give the asparagus plant enough space, you should use at least a 60-liter pot or container. The pot should be able to accommodate a minimum depth of 40 cm for the asparagus to grow well. Many people use a 60-liter or even 90-liter concrete tub. The advantage of concrete tubs is that they have a good height-to-width ratio and are not too expensive. The containers are just high enough to plant the asparagus at the correct depth, and the roots can also spread outwards. A 60-liter concrete tub can accommodate two plants, and a 90-liter tub can accommodate three. But any other large pot or homemade container will also work fine, as long as it has a minimum capacity of 60 liters and is at least 40 cm high.
Filling the container
You now have the right pot or container, but what are you going to fill it with? Asparagus prefers airy and well-draining soil, such as the sandy soil they grow in outdoors. So make sure your pot drains well, and if you're using a mortar tub, drill plenty of holes in the bottom. At the bottom of the pot, you can start with a layer of coarse gravel to ensure proper drainage. Fill the pot with high-quality potting soil and, if necessary, add 1/3 of compost.
Power supply
After the longest day of the year, asparagus needs a lot of energy to sprout again every year and survive the winter. The nutrients in the pot deplete over time, so you need to ensure they are replenished. This can be done by adding a fresh layer of compost to the pot each spring and providing some additional nutrients during the season in the form of organic pellets or a liquid feed that you can add to the water.
