Introduction

Hedgerows are one solution growers in Yolo County have found for maintaining field borders and other non-crop farm areas. By planting hedgerows of non-invasive native plants, they create wildlife habitat areas that attract beneficial insects and provide competition against invasive weeds. With careful establishment and management techniques, hedgerows can provide a useful and attractive alternative to continuously scraping, spraying and cultivating field edges and other "unfarmed" areas that would otherwise become sources of weed seeds.

What is a Hedgerow?

Hedgerows are lines or groups of trees, shrubs, perennial forbs or grasses that are planted along field edges or other unused areas. For agricultural areas in California, we recommend using a variety of native grasses, perennial forbs, shrubs and trees that attract different types of beneficial insects, mammals, reptiles and birds (including raptors). Native plants work extremely well in hedgerows because they require very little care after an establishment period of about three years. Many native plants have deep roots that hold soil and increase water permeability. Hedgerow areas suppress weeds by providing competition, and are less susceptible to wind and water erosion than bare soil. They can also filter surface runoff water, preventing silt, nutrients and pesticides from entering waterways, if properly situated.

Selecting a Site

Any unused farm area with good soil and access to water may make a good hedgerow site. Some of the native plant species that we recommend using in an insectary hedgerow are very water sensitive; some like a great deal of water, while others can develop root and crown rot if overwatered. In order to combat this challenge, we recommend using drip irrigation tubes with adjustable emitters. Drip irrigation is the most effective, efficient  and successful method of watering your new hedgerow. A secondary, very effective method is furrow irrigation. It is imperative to select a site that can be irrigated by one of these methods; access and availability of water to a new hedgerow planting is the single-most important factor in plant survival in the first year.

Another important factor in site selection is vulnerability to flooding and/or standing water.  If a site is known for its tendency to flood or have standing water during the winter months (or due to overwatering of a field crop), DO NOT use this site for a hedgerow planting. If possible, try to select a site that is either on higher ground or that you are absolutely sure does not collect water at any time of year. Of course, in high water years, this may not be avoided, but do not place a hedgerow on low ground and expect many of the plants to survive, unless you are specifically planting flood-tolerant species.

A third consideration is equipment. Make sure the area is out of the way of equipment; placing the hedgerow too close to a road or high-traveled area may be problematic if the equipment damages the plants. Hedgerows can certainly be placed next to roads, but recognize that many of these shrubs and trees will grow to 10-15 feet in width.  Be sure to leave enough room for this growth. This may mean planning spaces in the hedgerow for equipment to drive through or choosing an alternate site that would be less intrusive. 

Choosing Plants

Plants should be selected according to the purpose you want the hedgerow to serve, but local species are likely to be best adapted to conditions on your farm. It is important to look at the water needs of each plant. Some natives, such as toyon, wild lilac, and California buckwheat, are extremely drought-tolerant and will die if their root crowns get wet for too long. These are best planted in well-drained soils. Others, such as willows and cottonwoods, prefer wetter areas. Within a given site you may have varying soil types or lower areas that are more prone to flooding. In this case, choose plants with these difference in mind; i.e. select water-loving plants for some areas, and drought-tolerant plants for others. If you take the time beforehand to choose plants according to your site, rather than just using an "example" hedgerow recommendation, you will have much more success with plant survival; plants will grow faster, be healthier and be better able to resist disease and pest insect pressure.

If you would like your hedgerow to serve as a windbreak, then you should design a hedgerow with many tall-growing shrubs and trees. Recommended species include cottonwoods, willows, native oaks, redbuds and elderberry. Remember too that as these trees grow, their understory will be less vegetated and you may want to include shrubs in between trees to provide habitat and erosion control closer to the ground. By including shrubs, you will also gain more insectary value to the hedgerow. For lists of possible species for different settings in the Yolo County area, please see the attached list.

If your primary goal is to use plants to attract beneficial insects (i.e. insects that prey on or parasitize crop pests), you should plant species with plentiful nectar and pollen. If you are unsure whether a plant will attract beneficial insects, observe one during its flowering stage to see if bees and other insects are using it. For example, Ceanothous and Coyote brush tend to have large quantities of hoverflies and bees feeding on their pollen and nectar, whereas oleander bushes attract very few insects. Consider the time of year during which each species flowers, and try to use a good variety of plant species so that flowering will take place almost year-round. Many beneficials are looking for nectar and pollen in early spring and late fall, when nearby crops are just being planted or are being harvested. By using plant species that flower during these times, you will encourage greater use of the hedgerow, as these insects do not have other habitat in the area. 

Design, Site Preparation and Planting

Unless the future hedgerow site has been kept free of weeds, it is best to begin regular discing, burning and/or spraying at least one year before you intend to plant. Reducing the weed seed bank in this way will be especially important if you intend to plant grasses. Depending on the layout of your hedgerow and your irrigation method, you may need to prepare one or more planting beds for native grasses. Preparation for seeding is no different than preparing a seed bed for wheat, alfalfa or most other crops. It is important to cultivate the area, depending on the soil type, by discing thoroughly and then harrowing to prepare an even, well-drained bed that is free of large clods of soil that can impede grass germination.

The best time to plant native grass seed is during the fall. You may want to wait for a rainstorm to bring up the first flush of weeds and then spray, burn and/or harrow the weeds before planting. You can also control weeds in the first 1-2 weeks after planting by spraying glyphosphate before the native grasses emerge. Native grasses tend to take 2-3 weeks to emerge, but this is very weather dependent; be sure to inspect the site for germination before spraying. Native grass seed can be drilled but most often the seed is broadcast with the use of a "belly grinder" (available from an RCD or your native grass supplier). After spreading, the grass seed should be harrowed in lightly (only 1/8" is necessary) so that seeds won't dry out and die. If harrowing isn't possible, a light covering of hay can also be used. The harrowing can be done with a 4-wheel ATCV and light chain harrow, which also allows for getting on the site even after numerous rains. Please refer to the article "Strategies for Establishing California Native Grasses by Direct Seeding in the Sacramento Valley and Adjacent Foothills," available through the Yolo County Resource Conservation District for more specific instructions.

Most native forbs, shrubs and trees should be planted in the fall, although some become dormant at that time. Consult with your plant supplier for the best transplanting time. When planting, be sure to allow the shrubs and trees enough room to spread. A good rule of thumb is to plant them at centers 13-15 feet apart from each other. If you are using perennial forbs and small shrubs in your hedgerow, these can be placed in between the larger shrubs and trees, at a center spacing of 7-8 feet. This can be varied depending on the desired effect, but placing these plants any closer can inhibit growth in years to come, and is not necessary economically or physically.

Before transplanting shrubs and trees, you may need to pre-soak the area to be planted to make hole-digging easier. Pre-soaking holes before transplanting is also a good way to reduce the likelihood of transplant shock. You may want to consider using fertilizer tablets for woody shrubs and trees. Dig a hole about twice the width and 1.5 times the depth of the original root ball, drop the fertilizer tablet in, and cover with a small amount of soil so that the tablet is not in direct contact with the roots. Mound soil in the base of the hole so that the top of the root ball is roughly at the surrounding ground level. Remove the plant gently from its container and place it in the hole. If you need to loosen the root ball from the sides of the container, roll the container around in your hands, but never pull the plant out by its stem. Pack soil gently around the rootball to ensure good soil contact and minimize settling. Cover the top of the rootball with 1/4" -1/2" of soil to prevent it from drying out. Be sure not to cover the top of the root ball too much, especially if the plant is a drought-tolerant shrub; the soil can hold water against the root crown, killing the shrub. Soak the new plantings well to minimize transplant shock and settle any air pockets around the rootball.

Hedgerow Maintenance

Hedgerows need to be "farmed" during the first 2-3 years. This entails controlling invasive weeds and irrigating during dry periods. The most important maintenance that is necessary for hedgerow success is weed control and irrigation. Even though you've planted native grasses, shrubs and trees, weeds will still be a problem for several years.

Native Grasses: As previously mentioned under the Design, Site Preparation and Planting section, the first flush of weeds are typically sprayed with glyphosphate within 1-2 weeks of planting. After that you must carefully monitor weed pressure in native grass stands. In most cases, winter annuals such as Annual rye grass, Chickweed, Yellow star thistle, Annual sow thistle, Wild oats and mustard species can be prevalent and cause major problems. Since native grasses are slower growing, the annual weed growth can quickly surpass that of the natives and shade them out, thus preventing them from becoming established. Use selective herbicides for broadleaf weeds in the early spring to make sure they don't get too large and produce seed. Annual grasses are hard to manage but the best method is to mow your native grass stand before the annuals go to seed, rendering them incapable of reproduction the following year.

Hedgerow Plants: In the first year of growth, we have found that applying the pre-emergent herbicide Oxadiazon (granular formulation -- see label for application restrictions) along the hedgerow just after planting is the most effective in controlling winter annuals throughout the winter season and even beyond. You can use glyphosphate and 2-4D to spot spray (using a backpack-sprayer), but must be extremely careful to not hit any of the shrubs or trees with any of the herbicide. Be sure to spray on very calm days and use your judgment as to how close to a plant to spray. Hand-hoeing during the summer months, although labor-intensive, is very effective.

Irrigation: Find out the water needs of your plants from your supplier. Native grasses do not need summer watering because they become dormant at that time. Most shrubs and trees will need watering about every 2-4 weeks during drought months (March - November, depending on the year). After the 2-3 year establishment period, irrigation should no longer be necessary (depending on the plant species) and weed control measures can be considerably reduced. You may wish to keep notes on insect and wildlife visitation, weed problems and control methods you use in the hedgerow as well as weather conditions and plant species that seem especially suited to your area, so you can share your results with others. Yolo County RCD has planted several hedgerows and we would be very interested in hearing your questions and comments regarding your own hedgerow as we continue to monitor our hedgerows and work on improving establishment methods.