Growing asparagus from seed is a task well worth it. They are a wonderful perennial to have in the garden. If they are treated correctly they'll provide you for 20 years or more.
Asparagus need a forever bed to be planted in and should not be harvested in their first three years. They need that time to establish themselves.
Asparagus appreciate a really fertile, well-drained and weed-free soil. To achieve this, preparation is key.
At this time of year (late winter) asparagus crowns are selling in garden centres. Crowns are asparagus seedlings that are at least a year old. Though they save you some growing time, it doesn't give time to prepare the soil, especially if you follow no-dig garden practices.
Sowing and growing asparagus from seed this year and keeping them in pots until next year can give you plenty of time to prepare and nourish your asparagus bed.
Sow asparagus seeds in moist but well-drained seedling mix. The seeds will germinate best with temperatures of 17 degrees Celsius and above.
Once the seeds have germinated, keep them in a sunny spot and don't let the soil dry out. As the seedlings grow bigger they will need to be transplanted into bigger pots. Choose a pot that's 3-4 times bigger than the initial seed raising tray. This means you won't need to repot them again before they're planted out in the garden.
They can be hardened off when they are around 10 weeks old and moved to a greenhouse or outside until they are ready to be planted out. As they are in seedling pots, ensure they don't dry out.
Preparing Your Asparagus Bed
Find a sunny spot. Asparagus appreciate full sun in spring and summer.
Start layering on plenty of organic matter and continue to do so throughout the year. Aged manure, chopped seaweed, compost, grass clippings, shredded leaves….They need good drainage so the more friable humus you can create, the better.
Once the seedlings become one year old crowns they can be planted in their forever home, in late winter.
Don't plant too many if you don't have the space. They grow very tall and bushy when established so ideally you'll need at least 30-40cm of spacing between each plant.
To plant the asparagus, make a 10cm or so hole in the soil for each crown. Place the crowns in, fanning out the roots as you do so. Traditionally asparagus are planted in long dug-out trenches but I like to avoid that kind of digging and soil disruptment.
Once the the crowns are planted, cover with a layer of compost and mulch.
As the soil warms, spears will push through.
Any spears they produce in the first three years should be left to go to fern. These will feed the roots.
The ferns can be cut back in late autumn/early winter when they turn brown and start to die back.
Cover the crowns with a thick layer of compost and mulch once the ferns have been cut back.
When your asparagus get to harvesting age, only harvest them for the first few weeks in that first harvesting year. Choose those that are at least the thickness of a pencil.
From year four onwards you can harvest them until December. Then any others that pop through should be left to fern.