By Susanne von Rosenberg, UC Master Gardener of Napa County
One of the reasons I really enjoy having fruit trees is that they are perennials: they give back a lot for relatively little effort. You can get the same benefits from perennial vegetables.
The most common perennial vegetables for our area are artichokes, asparagus and bunching onions (scallions). Others that are highly suited to our Napa Valley climate are cardoon (a relative of artichokes), tree collards (also known as tree kale or walking stick kale), walking onions (also called Egyptian onions) and nopales (prickly pear cactus pads). Additional options include sunchokes (Jerusalem artichokes), perennial arugula (caution: it self-seeds readily) and miner's lettuce (claytonia). In our climate, miner's lettuce acts like a self-seeding annual, but it is a perennial in areas where it receives sufficient moisture.
In addition, you can “perennialize” regular kale, garlic (for green garlic) and, to some degree, Swiss chard and broccoli. To start treating regular kale as a perennial, simply cut it back to a few inches of stalk when it starts to look tired and it will resprout. You can do the same with broccoli. You won't get another large head, but you will refresh the plant and get more small side shoots.
In my yard, Swiss chard readily self-seeds, so there is always some chard growing wherever I water regularly. If it's not in the way, I let it grow. If you plant garlic and don't harvest the bulb, it will sprout as a cluster of green garlic the following growing season and continue to create bulbs underground. Eventually, as with flower bulbs, you will have to dig it up and divide it. Keep some of the best bulbs and replant some cloves for more green garlic.
Think about the pros and cons when you consider adding perennial vegetables to your garden. The main advantage is that you only plant once, yet you harvest for multiple years. Because the plants stay in place longer, they develop stronger and more extensive root systems. This helps the plants take better advantage of available water and nutrients.
Because you're not replanting every year, you're protecting the soil ecosystem. For busy people, adding one or two perennial vegetables per year can be a way of building a productive vegetable garden without investing a lot of time.
You can also let the plants flower, which supports pollinator insects. Some perennials add beauty to your garden. Sunchokes, which are part of the sunflower family, will grow 8 to 10 feet tall with adequate water and produce numerous small sunflower-like flowers.
However, there are some downsides. First of all, you lose flexibility. You have to carefully consider how big the plants will get and whether they make sense at full size in their proposed location. Good locations for perennial vegetables include areas adjacent to other perennials (including berries, fruit trees and ornamental plantings), at the ends of annual vegetable beds and in groupings with other perennials that have similar water needs.
For many perennial vegetables, it takes longer to get harvestable produce. Also, you may need to keep watering them when the weather is dry. When we have a light rainy season, you'll likely have to keep irrigating.
If you are not rotating vegetables and you are keeping them alive year-round, you may have more pest problems. Control pests as soon as you notice them. If you have gophers, you may find that certain perennial plants, such as artichokes, need to be planted in cages because the roots are just too tasty for gophers to resist.
Finally, because you are continuing to water, you are also likely to continue to get weeds, so you will need to cultivate around the plants or mulch regularly to keep the weeds down. Also make sure to check that you are selecting the right kinds of perennial vegetables for your garden. Many common perennial vegetables, such as watercress, require relatively high amounts of water or need sandy, well-drained soil. Others can become invasive. Do your research or contact the Master Gardener help desk for more information.
There are many other perennial vegetables to try if you're adventurous. On the border between herbs and vegetables are sorrel and lovage, which can be used as salad greens, in soups and as seasonings. Daylily tubers, young shoots, buds and flowers are all edible. The leaves of scorzonera (black salsify) can be harvested and eaten just like lettuce. (If you harvest the edible roots, however, you will kill the plant.) Sweet potato leaves are also edible, as are linden tree leaves. Have fun diversifying your garden!
Napa Library Talks: First Thursday of each month. Register to get Zoom link. Thursday, February 4: Soil is the Solution: Healing the Earth One Yard at a Time.
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.
- Author: Denise Seghesio Levine
If you are patient and forgo harvesting tasty green spears the first two years after planting, a properly sited asparagus bed can pay off in bountiful spring harvests of asparagus for the next 12 to 15 years. Some well-tended asparagus beds still produce after 25 years.
Asparagus is a hardy perennial that adapts to a variety of temperatures. But it is happiest in a climate like ours, where winters are cool and the ground might freeze just an inch or two.
When you are looking around for the best place to plant asparagus, keep a few things in mind. The vegetable wants plenty of sun and good drainage. And because asparagus beds last a long time, put them where they will not be bothered.
Even if home-grown asparagus won't grace your table the first two seasons, the plants provide beauty and interest in your garden. Asparagus makes a beautiful screen with soft, ferny foliage and red berries. But it is tall and can shade other plants, so plan accordingly.
If you prepare your asparagus bed correctly, you will not be digging it again for a long time. Break up the soil 18 to 24 inches deep. Add organic matter to feed the plants and provide good drainage. Aged manure, bone meal, blood meal, wood ashes, compost, worm castings and leaf mold are all good choices.
Dig in these amendments before heading off to the nursery. Asparagus crowns do best when you get them into the ground and watered soon after purchase.
You can start asparagus from seed—more economical than buying crowns—but you will need to wait an additional year before harvest. That's why most gardeners plant one-year-old crowns. At the nursery, choose plump, grayish-brown crowns that look healthy. Remove any rotten or dried roots. Plant crowns 12 inches apart; measure and mark the planting spots before you head to the nursery.
To plant, dig a trench 18 to 24 inches wide and set that amended soil aside. Return 2 to 3 inches of the amended soil to the trench spreading it along the bottom of the bed. Gently spread the roots of each asparagus crown over the mound so the crowns are slightly above the roots. Cover the crowns with 2 to 3 inches of amended soil and firm it well. As the asparagus begins to grow, add more amended soil to the trench to cover the exposed crowns until the trench is filled. Water as needed if nature doesn't.
To maintain your asparagus bed, weed thoroughly in the spring. Pull weeds gently instead of hoeing to avoid damaging the fragile new growth underground.
Do not harvest the first year after planting. The second year, harvest only lightly. Newly planted asparagus grows long storage roots. These pencil-thin, fleshy roots store the carbohydrate synthesized from sunlight that the ferny foliage captures all summer long. The following spring, this energy pushes up through the earth in exuberant growth. It is an amazing thing to see fresh asparagus spears push toward the light, sometimes growing a foot a day.
When it is time to harvest, snap off 6- to 8-inch spears at or below the soil surface. The plants can get away from me, and I am not averse to using spears that are up to 18 inches tall. But the stalks still have to snap off to make it to my kitchen; if they don't, they aren't fresh. Harvest daily in season and use immediately, or refrigerate in a plastic bag for a few days. Asparagus freezes well and can be steamed, baked, braised, grilled and used in cold and hot soups. Pickled asparagus is wonderful for appetizers or Bloody Marys.
After the harvest, let the ferny foliage grow. Female plants set attractive red berries. When the ferns start to yellow and die, or if there is an early freeze, cut the foliage back to 2-inch stubs.
Some people have a reaction to eating asparagus; it's harmless but hard to ignore. We will not talk about that, however. You know who you are.
Workshop: The U. C. Master Gardeners of Napa County will host a workshop on “Drought-Tolerant and California Native Plants” on Saturday, October, 3, from 9 a.m. to 11 a.m., at Pope Valley Fire Station, 5880 Pope Valley Road, Pope Valley. Learn about drought-tolerant and native plants and discover the elements that help them thrive in our Mediterranean climate. Learn how to use them in your own garden to replace some of your thirsty ornamentals. You will also learn about irrigation modifications to make your water use more efficient and effective.ONLINE REGISTRATION
This is a free workshop but pre-registration is requested. A minimum of 10 attendees is required or the workshop will be canceled.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.org/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.