Asparagus is a perennial plant (it comes back year after year) that grows well in cool climates. Growing asparagus year after year requires little effort once your asparagus bed becomes established in the right area. Asparagus can be grown from seed, crowns or dividing (propagating) older plants.
This spring will be my 3rd year growing asparagus in Alberta, Canada in my backyard raised bed garden. I am anxiously anticipating being able to harvest asparagus for the first time this year. I am growing asparagus both from seed and from crowns. I tried a few crowns in the ground and a few in a raised bed. Both seem to be doing very well.
Asparagus Growing Time
Asparagus crowns are generally sold as 2 year old asparagus plants that have begun to established a root system. Growing asparagus in your garden is a lesson in patience as you don't harvest asparagus until the 2rd year if you are planting crowns, or the 4th year if you are growing it from seed.
Asparagus Growing Requirements
Most asparagus is hardy in gardening zones 3 to 8.
Do not take the decision of where to plant your asparagus lightly. Although it takes a while to get established, an asparagus plant will keep on producing for up to 20 years. It is best not to move it during that time so take care when deciding where to establish your asparagus patch.
It is ideal to prepare the soil in the fall if you plan to plant asparagus crowns so that they can be planted outdoors in the spring as soon as the soil is workable down to a depth of 18 inches. For me in zone 3 Calgary Alberta, the ideal time to plant asparagus crowns would be the end of April.
Asparagus grows best in loose, well drained soil free of other roots, rocks, and weeds. Select a location that receives at least 8 hours of sunlight. Asparagus prefers a soil pH between 6.5 and 7.0 Add compost deep down into your soil prior to planting your asparagus.
Asparagus is most often grown in an in-ground garden but asparagus can also be grown in a raised bed (as long as it is a raised bed that is connected to the ground). When growing asparagus in a raised bed it especially important to mulch it in the fall with about a 4 inch layer of straw or leaves. The mulch will help protect it from the winter elements.
Growing Asparagus From Crowns
Most people choose to grow their asparagus from crowns as this gives a year head start towards harvesting time. Asparagus crowns can be ordered online or bought from most garden centers.
If you purchase asparagus crowns early in the spring before the ground has fully thawed, plant them in a pot with soil as soon as you bring them home. Keep them in a cool place like a garage until you are able to plant them outdoors.
How to Plant Asparagus Crowns
Soak asparagus crowns in water for 15 minutes prior to planting.
Plant asparagus crowns 18 to 24 inches apart in trenches 15 inches deep.
Cover the crowns with 3 inches of soil.
As the asparagus plant sends up shoots begin to add 3 inches of soil every few weeks until the trench is filled. Make sure you don't add so much soil you are completely covering the shoots.
Maintain your asparagus bed to keep if free of weeds and debris.
How to Plant Asparagus Seeds
Plant asparagus seeds 8 to 10 weeks before you last frost. I aim to start my asparagus seeds between February 14th and 21st.
Soak seeds in water for 2 to 6 hours prior to planting them.
Plant seeds 1/2 in deep.
Plant 1 seed per 2 inch pot.
Plant your asparagus starts 18 inches apart in trenches 15 inches deep.
Every 3 weeks add 3 inches of soil until the trench is filled.
It is important to wait until your asparagus plant is established before harvesting asparagus spears. Leaving the spears allows the plant to put more energy into root growth. Harvesting asparagus spears too soon can result in killing the plant.
You can harvest asparagus the 2nd year after planting crowns or the 4th year after planting seeds. Harvest spears when they reach a diameter larger than a pencil and when they are 6 to 10 inches tall. Once your plants are well established, the harvesting period for asparagus can last for 6 to 8 weeks. New spears grow quickly, almost every day.
As the spears begin to get smaller, stop harvesting and leave them to grow into fronds. These asparagus fronds provide nutrients to the plant's roots for the rest of the growing season. Asparagus fronds can be trimmed back once they turn brown in the fall.
Male and Female Asparagus Plants
Asparagus plants come as either male or female plants. Because the female plant puts energy into reproduction (by way of developing seeds), female asparagus plants produce fewer spears. It can be beneficial to remove female asparagus plants and replace them with higher yielding male plants. Male asparagus plants can produce up to 3 times the amount of spears as female plants. When you order crowns from greenhouses, they usually sell select varieties that are primarily male plants. When growing asparagus from seed, you will have an equal ratio of female and male.
If you would like your asparagus to reseed itself, consider leaving a few female plants in your patch.
Both male and female asparagus plants produce flowers but only the female plant produces small red berries that carry the seeds. When the berries are visible, mark the plants and if you wish to remove them, do so early the next spring. When removing female plants from your asparagus patch try not to disturb the roots of the rest of the plants any more than you have to.
(*Caution* Asparagus seed pods/berries, though attractive, are considered toxic and should not be eaten. They are known to cause gastro-intestinal symptoms. Do not allow children to consume them.)
Companion Plants For Asparagus
Asparagus grows especially well interspersed with strawberries. Because strawberries have relatively shallow roots and grow low to the ground they can share a space together. Wait to plant strawberries until the year after planting asparagus.
Other companion plants for asparagus include basil, nasturtiums, parsley, strawberries and Tomatoes.
Avoid planting asparagus near onions, garlic or potatoes.
Print off my full Companion Planting Chart for reference.
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