Asparagus: Best Practices for Longterm Success
So you’ve got your asparagus patch planted. Maybe it’s a few years out and it is producing well. What a thrill to have this vegetable just wake up in early spring and provide some of the first nourishment of the season year after year. We are quite enjoying our rather large patch of homegrown asparagus this month, and I wanted to share some of our best practices for keeping our asparagus bed healthy as well as some strategies to keep the pests at bay. Because like with any other crop, there are a few insects who are as attracted to these spears as we humans are.
Being a deeply rooted perennial, asparagus needs inputs every year to produce well and put ample energy back into its spear-producing root system for next year’s crop. I’ve heard from many different home gardeners who all have secrets to feeding their asparagus and there are key threads to everyone’s approach.
Compost! Every asparagus bed needs a good few inches of compost applied annually. We like to apply it in early spring before the plants emerge as it is easier to apply compost across the 5-foot wide bed before the plants are actively growing. If you have an asparagus patch, you know what kind of a summer tangled mess it becomes by August (or sooner in warmer climates).
Fertilizer: We broadcast apply 1-2 gallons (10-15 pounds) of our slow release organic fertilizer over our entire bed in spring, which is about 200 square feet.
Irrigation is another key ingredient to asparagus success. If you don’t get summer rains, be prepared to irrigiate as asparagus roots can go four feet deep and require deep waterings to develop strong, healthy root systems that will be producing for several decades to come. We supplementally water as needed in summer.
Weeding is huge. Like with any other food crop, weeds will compete for sunlight and nutrients and should be eliminated or at least minimized in order to maintain the strength and health of the asparagus plants. With a perennial that needs to replenish its roots each summer, it is even more important, so prioritize your asparagus patch and you will get the most out of your investment with large spring harvests and decades of productivity. A weed in this bed would include asparagus seedlings, so if you have female plants, remove their offspring annually.
The notion of companion planting comes up from time to time in discussions with asparagus patches and I’ve been asked about it numerous times. I’ve read about some large scale farmers who plant clover between their asparagus rows and then till it under in fall as mulch. I’ve even heard of interplanting things like tomatoes with your asparagus to repel the beetles. We tend to err on the side of less is more with this bed. Given the longevity expectations of asparagus as a perennial vegetable, we set aside land just for this crop, devoting inputs just for their maturing roots to grow strong, healthy, disease resistant plants for hopefully many decades to come. We minimize competition from other plants, giving them all the square footage for their growth and benefit.
Pests: The Common Asparagus Beetle
We knew about this potential pest before it arrived, but were nonetheless floored when we planted an asparagus patch where turf once was - and the beetles located it within mere months of establishment. You may have asparagus beetles in your asparagus patch and not yet realized it. Do some of your spears grow with a hooked tip? This is one of the key signs you have asparagus beetles feeding on your plants.
Common asparagus beetles overwinter in litter, like many other pests — and a lot of beneficials — and emerge from their winter hibernation in early Spring around the same time the asparagus begins to emerge. Conveniently, these beetles will happily overwinter in the standing dead asparagus stems, giving them a head start next spring with a very short commute to their next meal. So while you read a lot about leaving plants standing to provide insulation, if you are faced with an outbreak of asparagus beetles, err on the side of caution and remove all dead plant material in late fall.
Another sign of asparagus beetle damage is browning on your spears. That being said, the hooked spear and the beetles themselves are much easier to spot in early Spring, so those are the two signs I keep an eye out for each May. We have already interrupted several busy beetles in the asparagus patch last week, hopefully disrupting their already bustling lifecycle.
The other somewhat easy way to recognize whether the asparagus beetles have met your asparagus or not yet is to look for small, oval eggs that are laid perpendicular to the spear, usually near the tip of the spear. They are cream colored at first, maturing to a dark brown.
Note: there is another beetle known as the spotted asparagus beetle, but it’s not as common. Like with the eggs, if and when I come across and photo-document it, I will update this post with more information.
Cut down your dead asparagus stems to the ground level and remove all debris in fall. This is a best practice you should adopt annually to minimize overwintering adults that may have burrowed in the stems when the weather started to turn colder. We choose to haul it offsite to our local brush site to minimize any risk of being a harbinger for overwintering adults, trying to make it as challenging as possible for them to get a stronghold in our asparagus patch.
Develop a rhythm for amending your bed which should include slow release fertilizer and compost as well as a strategy for weed suppression. This can be accomplished in late fall or early Spring. Be consistent once you start adding the inputs, and maintain a weeding schedule all summer long. We find with a heavy layer of compost as mulch, our weed pressure is very low though we do weed regularly throughout the growing season.
Be proactive in monitoring your asparagus patch for signs of beetles, eggs, or damage. This is a key practice for any organic garden. We do daily walks, inspecting all our plants, observing any signs or symptoms of beetles or their damage. It starts within the first week of spears emerging and continues all summer long.
It becomes a little trickier as the asparagus patch matures, but I love engrossing myself in the middle of the asparagus fronds. It is its own ecosystem; I immerse myself in the middle of the bed - and always run into someone new I haven’t seen before in our garden. Summer is when you will be able to catch many sluggish larvae as well as adults, and wipe eggs off. It’s not an onerous task, but instead a quiet meditation we repeat daily, and is very manageable just by doing physical removal once a day throughout summer. We prefer this method to any type of spray, even organic.
When you locate asparagus beetles, use a bucket of soapy water and drop them into the bucket. They can be rather quick bugs to catch, so we find early morning and after supper to be the best times to successfully drop them in our pail of soapy water. Best to come at them with a hand from above and the bucket below, leaning the branch down toward the bucket in hopes gravity will encourage them to plop into the suds.
Beneficial nematodes, while not inexpensive, can be an effective biological control for common asparagus beetle larvae. You can order and apply the species Heterorhabditis bacteriaphora (Hb) to the bed by following the instructions in the package. Beneficial nematodes are efficient soil predators of larvae, and there are different species who specialize in different areas of the soil horizon, thus being more useful for certain pests who live either shallower or deeper in your soil. We applied beneficial nematodes to our soil for cabbage root maggots and Japanese beetles last year and look forward to seeing how well it worked this season.
Beneficial insects such as lacewing or ladybug larvae are excellent hunters of asparagus beetles at all stages of life. These are another biological control that can be ordered online and arrive with time-sensitive release instructions. We released lacewing larvae last Summer to hunt in our asparagus patch and noticed them in our garden for most of the Summer, which means they found plenty of things to eat and were incentivized to reproduce. They are one of the top insectivores to have in a veggie patch for pest management.
Other insects who work to help curb the asparagus beetle population are the tachinid flies and the parasitoid wasps. Unlike lacewings, ladybugs, and beneficial nematodes, these must be attracted to your garden by planting a diverse array of flowers throughout your garden. If you plant it, they will come. Interplant as much as you can around the garden so the adults are incentivized to not only sip nectar but also lay some eggs and help you naturally manage garden pests. The most beneficial flowers are those shallow, simple flowers such as sweet alyssum or anything in the Umbelliferae family (carrot, yarrow, parsnip, dill, fennel).
We hardly ever resort to any kind of organic sprays in our garden, and have never even entertained the need for asparagus beetles. Hand-picking is our top choice for pest management for asparagus and Japanese beetles and other pests like cabbage moths. I am quite certain there would be organic sprays marketed for asparagus beetles, but we have found it manageable to spend a little time each day tending our little patch of Earth searching for these insects and reveling in all the beauty we find along the way.
I don’t expect to fully eradicate the asparagus beetle, but my goal is that through time and the addition of more nectar for naturally-occurring insectivores and parasites, we will eventually arrive at an ecosystem that self-manages pest outbreaks with our endemic insect populations that have come to take up residence here.