Landscaping berms are mounded hills of soil that can serve multiple functional and aesthetic purposes in the garden. A berm can be placed to block or change the flow of water across the property. It can prevent water from draining back toward a house foundation or prevent water from puddling in the wrong place. In an area of heavy soil, a berm can improve drainage to accommodate plants that require faster-draining soil. A berm can also improve an area of poor soil. Berms can be used to form “islands” of landscaped areas within larger and mostly un-landscaped areas.
Building a berm in your yard is a good do-it-yourself project, as long as you keep the berm to a manageable size. First, decide where you want to place the berm, taking into account how it might affect the movement of water across the space. Then determine the size and shape you want for the berm. An asymmetrical shape is generally more pleasing than a circular one. A good rule of thumb is to make the berm about four to six times longer than it is wide. A kidney shape works well for a berm at a corner of the yard. The berm should not be more than 18 to 24 inches tall, as a higher berm might be subject to erosion. Use a garden hose to lay out the size and shape of the berm. Make larger curves rather than tight turns.
If the berm isn't very tall and the slope is gradual, edging usually isn't necessary. If the berm is taller or has a steep slope, you may need a retaining wall to help keep the berm in place. A short wall of flagstones, dry stacked three to four deep, is all that's required. Or you may want to use stones or bricks to separate the berm from the surrounding area, even if they aren't necessary. On the other hand, you might prefer a more natural transition from ground level to the berm.
Once you have constructed the berm, it's time to add plants. Put taller plants at the back, especially if you are trying to create privacy or screen an undesirable view. Shorter plants work best on top and down the sides. Let trailing plants spill over rocks or trail downhill. Ornamental grasses work very well in a berm as their long roots can resist erosion and help hold soil in place. Select plants that look natural together: for example, cactus would look out of place planted next to a rose bush. Research the size of plants at maturity so you leave enough space between plants for them to grow without crowding each other.
Get inspiration for your berm garden design from the two berm gardens at the Master Gardeners Demonstration Gardens at Patrick Ranch (10381 Midway, Durham). The Berm Garden is just east of the Visitor Center. It has a retaining wall about three feet tall surrounding most of the garden, with the soil sloping to ground level on the open side. The Native Plant Garden is mulched with red lava fines (particles), against which the colors of the native plants “pop” when they are in bloom. The Demonstrations Gardens are free and open to the public on Saturdays and Sundays from 11am to 3pm.
Puncturevine (Tribulus terrestris) is an attractive green plant with small yellow flowers commonly seen growing prostrate along the side of the road. A native to Southern Europe, it's also referred to as “goathead.” However, underneath its foliage lies danger: spiky seedpods with needle-point spikes. If puncturevine is stepped on, it is painful to bare feet and dogs' paws; it will pierce and flatten bicycle tires. Because of its spiky seedpods puncturevine is also referred to as “caltrop,” after the spiked metal devices thrown on the roadway to stop vehicles. Caltrops have four projecting spikes with one spike always pointed up; just in the right position to puncture a tire or flip-flop, hence the similarity to puncturevine seedpods.
Unfortunately, there are is no easy way to control this noxious weed. For most homeowners, the mechanical control methods of hand removal or cutting the plant off at the taproot are most effective. Any seeds left on the ground must be removed by raking or sweeping. Use heavy gloves to protect hands from the spiky seedpods. Of course, as with any weed, it's best to remove it before it flowers and sets seeds. This is especially important for puncturevine, as seeds are viable for years, and can be spread by shoes or the wheels of lawn mowers or carts.
Biological control using several species of weevils have been tried but are not always effective. Chemical control of puncturevine in the home garden is often unnecessary. However, in heavily infested areas, or when hand removal is difficult, herbicide may be an option.
For more information on puncturevine see the IPM Pestnote No. 74128 on Puncturevine.
Summer has arrived and so has the dreaded, prickly presence of yellow starthistle, Centaurea solstitialis. Reports indicate that yellow starthistle infests between 10 and 15 million acres in California, making it the most wide-spread noxious weed in the state.
The foliage of this plant ranges from gray-green to blue-green; once flowering begins it can easily be identified by its bright, thistle-like yellow flowers, which have sharp spines surrounding their bases. This weed grows from 6 inches to up to 5 feet.
Yellow starthistle forms dense infestations and rapidly depletes soil moisture, preventing the establishment of other species. It is also poisonous to horses, causing a nervous disorder called “chewing disease” (nigropallidal encephalomalacia), which is fatal once symptoms develop. Horses are the only animal known to be affected – they should not be allowed to graze on yellow starthistle.
Yellow starthistle can be spread as a contaminant in grass seed and in all classes of hay, particularly grass hay. Hay used as mulch along roadsides or disturbed areas can be a source of yellow starthistle. Livestock that have fed in areas infested with yellow starthistle can be transporters of the seed.
Because the seeds germinate during the rainy season, a single cultivation after the rainy season, when soils are dry, effectively controls yellow starthistle seedlings and rosettes. Timing is critical: this cultivation must take place in late spring after the last rains but before seeds are produced.
Mowing can be used to manage starthistle. Be sure to mow well before starthistle is in full flower or has set seed. Mowing is most effective when soil moisture is low and no irrigation or rainfall follows mowing. If rain occurs after you've removed existing plants, seeds will continue to germinate and the eradication process must be repeated. Pre-emergent and post-emergent herbicides can also be helpful in controlling growth and infestation of starthistle.
Lastly, effective management of starthistle includes revegetation. Planting affected areas with desirable plants discourages starthistle regrowth by creating competition.
For information about herbicides and for photos of yellow starthistle's growth cycle, see the UC IPM Pest Note on Yellow Starthistle.
UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at (530) 538-7201. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.
Every gardener knows that weeds are just plants in the wrong place. Webster's dictionary defines a weed as “a plant that is not valued where it is growing and is usually of vigorous growth; especially: one that tends to overgrow or choke out more desirable plants.”
Some weeds, those with large root systems or a taproot, penetrate deep into subsoil, breaking up compaction, which helps drainage and new growth. This deep penetration enables weeds to accumulate trace elements from the subsoil, and bring them to the soil's surface. The plants then die back and decompose, becoming what is called green manure.
The primary value of weeds, wrote the eminent U.S. botanist Frederick Clements in 1920, is to “reveal information about the health and pH of our soils.” For example, certain species are confined to acidic soils and others to alkaline.
The use of weeds as soil indicators is not a new idea. Many early North American immigrants to the eastern United States chose land for their farms according to the weeds, plants, and trees that it supported. Conifers were characteristic of sandy, acidic soils that had little agricultural value. Birch, beech, maple, and hemlock indicated fertile soil. They learned that the tall-grass prairies were suitable for cereals, hay, and orchards. The bunch grass regions were better suited to wheat and grass.
Another useful indicator comes from growing hydrangea, a beautiful and common flowering plant. If your soil is acidic the flowers will be blue. If your soil is more alkaline the flowers will be pink.
Ehrenfried E. Pfeiffer, a European scientist and student of Rudolf Steiner, wrote an entire book on this subject in the 1950s: “Weeds and What They Tell Us” (still in print). According to Pfeiffer, sorrel, plantain, horsetail, and knotweed are found in acidic soils. Dry soils with very little humus might support mustard, thistle, broom, and St. John's wort.
Sandy soils will have goldenrod, aster and toad flax. Alkaline soils support chicory, spotted spurge, sagebrush and woody aster. In heavy clay or compacted soil you might see morning glory, plantain, Bermuda grass, chickweed, and dandelion. Dandelions also indicate low calcium in the soil.
Identifying the weeds in your garden can be fun! In some cases knowing what their presence indicates may help you manage your soil. Controlling weeds by hand weeding or with herbicide before they seed will reduce future populations if done consistently from year to year. One year's uncontrolled weeds can produce seven years seeds! You may even develop a new appreciation for weeds.
For more information about weeds or help identifying them; see the UC Statewide Integrated Pest Management website on weeds.
UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at (530) 538-7201. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.
The devastating Camp Fire of 2018, along with the numerous fires North State residents have experienced since then, have led many of us to focus on creating a defensible fire-resistant landscape around our homes. As noted in this column last Friday, the key to establishing defensible space is to utilize plants that are fire resistant and judiciously space them both horizontally and vertically.
Shrubs that are fire resistant include ceanothus, butterfly bush, spirea, rose of Sharon, Oregon grape, lilac, mock orange, potentilla, forsythia, cotoneaster, island bush poppy, currants, camellia, azalea, monkey flower and viburnum. Aloe and other succulents are generally considered fire-resistant but avoid succulents such as ice plant that produce mats of flammable dry material.
Highly flammable plants often have an excess of fine dry or dead material and contain volatile waxes, terpenes, or oils. Their sap is gummy or resinous and aromatic. They may have loose, papery bark as well. Examples of flammable plants are sagebrush, conifers (cedar, pine, juniper, fir, Italian cypress), broom, rosemary, eucalyptus, palms, feather and fountain grasses and dry annual grasses. These plants should be avoided when planning a firewise landscape; if they already exist in a landscape, consideration should be given to removing them.
For more information on creating fire resistant landscapes, see the Firewise section of our website devoted to this topic.
UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at (530) 538-7201. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.
