Skip to main content

Asparagus

Updated December 04, 2018
Thumbnail

David Graper

SDSU Extension Horticulture Specialist & Master Gardener Program Coordinator

Young man purning asparagus bush with sheers.
A sharp pruning sheers is the best tool to remove the ferny stems.

A hard freeze has finally taken care of any remaining green foliage on most herbaceous plants and deciduous trees, including the foliage of a favorite perennial vegetable – asparagus. While many people rely on the “wild” ditch-grown asparagus, many gardeners cultivate asparagus in their own gardens. It is certainly nicer to be able to just go out to your garden and harvest some of the fresh spears then to go hunt up some in a ditch or fence row that might have already been harvested by someone else.

One of the keys to growing healthy asparagus is to allow the plants plenty of time to develop the big ferny stems, starting about the first of July. This ferny growth produces the carbohydrates that the plant needs to grow and also store up for the winter and next year’s initial crop of spears. If you harvest too late into the summer you may find that the diameter of the spears gets smaller and smaller, indicating that the plant is running out of stored carbohydrate reserves. If you see this happening, stop harvesting earlier in the summer and be sure to allow those big ferny stems to grow up for the rest of the summer and fall, until they finally freeze later in the year.

Asparagus can have a pretty yellow-orange fall color, so it can be a nice addition to the fall garden. But, once it has changed color and starts dropping its tiny, needle-like leaves, the stems are pretty much done manufacturing carbohydrates for the season. You can then decide if you want to remove the old stems this fall or wait until spring. I can tell you from my own experience that the old stems make a very effective snow fence. That can be a good thing if you have plants on the downwind (usually SE side) of the asparagus that you would like to provide some extra winter protection or moisture for next spring. The accumulated snow will also help to keep the soil cooler, later into the spring. This will delay initial shoot emergence and reduce the chances of having freeze injury to those first tasty shoots. But, if the drift of snow ends up on your driveway, you will wish that you had taken the time to cut it down in the fall. Again, I know this from personal experience!

Cluster of asparagus stems cut off near the ground.
Cut off the ferny growth close to the ground to not leaves stubs that could interfere with next year's harvest.

Disease is another reason why you might want to cut down the asparagus in the fall. Asparagus rust and purple spot are the most common diseases you are likely to encounter. Spores of these disease pathogens can overwinter on the old stems. By cutting them down as soon as they have been hit with a hard freeze, and getting them out of the garden you will help reduce the incidence of the disease the next year.

When you cut down the asparagus stems, cut them close to the soil surface. If you leave stubs that are a couple inches long, these will get in the way when you harvest next year. Keep that in mind when you are harvesting next year too, cut down close to the soil or even below the soil line to get the most of the spear you can and avoid leaving stubs behind.

Cluster of Shepard's Purse near a planting.
Sheperd's purse is just one of many winter annual plants that starts growth in the fall then flowers the next spring.

This can be a good time to take care of some weed control too. Once you get the old asparagus stems out of the way, you can dig out some perennial weeds like dandelions and sow thistles with a dandelion digger. You can use a hoe or hand trowel to cultivate or dig out winter annuals like shepherd’s purse, pennycress and downy brome.

Downy brome disease symptoms near a planting.
Downy brome is another winter annual that can be dug out or treated with an herbicide like glyphosate.

Non-selective herbicides can be used to treat weeds along the perimeter of the asparagus bed to keep them from spreading into the bed. Do not get any of the herbicide on any remaining green shoots or even green stubs from the shoots you might have pruned off. It’s also a good time to apply an organic mulch of compost, some of those shredded leaves from the lawn or straw. These will also help to keep the soil cooler in the spring and also help to deter weed growth next season.

Asparagus is a delicious and easy-to-grow vegetable that can provide food for many years to come if given some good basic care.