It's easy to grow green and delicious asparagus
Success with your asparagus is first and foremost about the right soil.
White or green asparagus, no it's not two different varieties, but two different cultivation methods. For many years, it was very popular, and perhaps also a bit fancier, to grow white asparagus instead of green. Today, the choice is probably more traditional. Maybe it is precisely the cultivation method for the white ones that has given the impression that asparagus is difficult and demanding. However, it is very easy to grow asparagus once you have made the right preparations. Cultivating white asparagus requires some soil work and moving around the soil a couple of times during the season. As soon as the asparagus stem emerges from the ground, a 30 cm high and 60-70 cm wide embankment is laid over the stalk. The asparagus then continues to grow under the embankment. When it emerges again, it is ready for harvesting. This is done with a long asparagus knife that reaches down to the bottom of the embankment, where the stem is then cut and pulled up. Because it has not received sunlight, it is white and long, and it also needs to be peeled. When asparagus season is over around mid-June, the plants are allowed to grow large, and the soil is levelled out, and then it's back to the beginning again next year.
Into the light
The method is a bit difficult and space-consuming, and not really necessary because the green asparagus that is not covered with a soil embankment tastes just as good and does not need to be peeled. Furthermore, the green asparagus contains more vitamins than the white ones.
There are, of course, different varieties of asparagus, but that's another matter. Some varieties are suitable for both white and green asparagus, while others are specifically developed for green asparagus and do not like a heavy cover. Others thrive well in the dark and are therefore more suitable for white asparagus. Varieties aimed at white asparagus often have thicker violet shoots, although the colour disappears during cooking.
Choose a variety you like
An asparagus bed can be kept alive between 10 and 15 years. That is why, the taste of the variety you plant, can play an important role. It is about growing asparagus that you find delicious. The variety “Mary Washington” is very popular and is suitable for both green and white asparagus, but otherwise, I recommend keeping an eye out for the variety you buy from the local greengrocer and that you think tastes good. Then you can check the variety. Unfortunately, it is not always indicated, but the greengrocer should be able to tell you.
The basis for success is your soil
Asparagus can withstand salty air. Its natural habitat is the beach, where the soil is also quite rich in calcium due to the many washed-up shells. Therefore, the biggest job is preparing your soil. It should be slightly basic. Often our garden soil is the opposite or at best neutral, but here the pH value should be 7.5. A high or low pH can be good for something and bad for something else. The pH value is important for the soil's minerals and for the ability to release the nutrients that the plants need. It's also not completely irrelevant whether your soil is on the sandy or clayey side. If it's on the sandy side, the pH value can be a bit lower. In a sandy soil, asparagus thrives at a pH value of 6.6-7, while in a clayey soil it should be at 7.5.
Take a sample
First, you need to measure the pH value of your soil. You can buy a pH measurement kit at a plant nursery, so you can read the value. For example, you mix 50 grams of soil with 50 ml of demineralized water and dip a litmus paper into the water. The paper then shows on a scale what the pH value of the soil is.
If the pH value needs to be raised, you can do so with garden lime. On sandy soil, you should expect to use 30-40 kg per 100 square meters to raise the pH value by half a unit. On clayey soil, it takes 50-60 kg.
Hanne Søgård, who is an agricultural technologist, recommends adding the garden lime to the soil over the period of several years, so the soil is not going into shock. If the pH value is as low as 4, for example, and needs to be raised to 7, she would suggest giving lime in November and again in June-July, but only half the dosage in the summer months. That is 50kg in November and 25kg in June per 100 square meters. Check again the following year and use the same dosage method until the balance is achieved. If the pH value is too high, it is very difficult to lower. Here, you can use leaves and sphagnum moss.
Note that the specified pH values are for your asparagus. In general, you should be careful not to let the soil move too far above a pH value of 6 if you want to grow organically. Liming can involve significant changes to the soil organisms that are important in organic farming. A big part of the nutrients for the plants comes from these organisms and not just from fertilizer.
You're almost done with the preparations
The next step is to ensure that there is no perennial weed in your bed. If perennial weeds get in between the asparagus roots, they are difficult to get rid of again and your asparagus bed will end up being a weed field. Therefore, be diligent in removing everything.
Seed or plant
You can sow asparagus seeds if you have a lot of patience, but it takes four to five years before you can enjoy them. If you choose to sow, do it in April. Place the seeds in 2 cm depth in seed trays and place them in the greenhouse. Plant them out when they are sufficiently grown, with 33 cm spacing between them and 140 cm distance between the rows for green asparagus, 190 cm distance for white.
The first harvest
If you buy two-year-old plants, it goes faster, but you can first harvest them in the following year the earliest. Since the article primarily deals with green asparagus, in principle, you can dig a large hole like you do for any other plant, but it is more practical to dig a 25-30 cm wide and 30 cm deep trench. In the hole, let the bottom curve a little. This makes it easier to spread the roots. Be careful that the roots do not dry out. Cover with 10 cm of soil, and as the plants grow, cover them with the rest of the soil.
Only when the plants are three years old, preferably four, can you harvest. The green asparagus is broken or cut when they are 10-25 cm long and before they begin to open up. If you take the first asparagus when the plant is three years old, you should be content with two pieces per plant. You can harvest until the middle of June and then the plants should grow freely again, to gain new strength. Male plants that yield the most produce red berries. When you buy asparagus, it is typically a nice mix of both male and female plants.
Maintenance: watering and fertilizing
In the first year, you should keep an eye on the watering. The asparagus should not be over-watered, but neither should they lack water. If you have the opportunity to get some seaweed, your new beach plants in the garden will enjoy the domestic surroundings with seaweed over the soil, ideally in May. Compost can also do the trick. The pH value drops year after year with added compost, so sprinkle a little lime on as well.
The worst enemy is probably the asparagus beetle. It is 5-6 cm long with a blue-black cross on its back. It lays eggs on the plant in the spring and eats its way into the plant's top. It is very important to check the plants for eggs, because when the larvae hatch, it is usually too late.
Asparagus rust gives cinnamon-brown, slightly elevated spots on the stems and can be a sign of too much water. Cut the infected plants down and bring them completely out of the garden. Just before winter, you can prevent rust by cutting the plants down and making sure they do not lie in the compost.
Asparagus secretes sulphur
Asparagus is healthy for our entire digestive system and contains all the important vitamins we need. You have probably noticed that your urine smells different when you have eaten asparagus. This is because asparagus contains a sulphur-containing acid called asparagus acid, which breaks down into water shortly after consuming asparagus. Enjoy that it is good for your whole system.
Om Lars Lund
Danish horticulturist and journalist
Lars Lund has for many years engaged in the garden and greenhouse. Lars has published many books about greenhouses, and he has participated in many Danish horticultural TV shows. He is a walking garden encyclopaedia, and he has answers for most basic cultivation questions – also the more ambitious ones.
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