Advice for the Home Gardener from the
Help Desk of the UC Master Gardener
Program of Contra Costa County
Client's Request: I have some sandbags that we filled at a City facility. A few of them have broken open, and I wonder if the sand is bad for the soil. I suspect if the sand is from an ocean beach, it is possible it could contain too much salt. How can I tell if it is OK for my garden? If it is OK, I may break open some remaining bags and set a few pavers in it.
Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your questions about using sand in your garden.
Presuming that you have clay soil like most of us do in Contra Costa County, the addition of sand to your soil will not be beneficial for soil health and in fact can harm your plants. The reason for this all relates to the soil texture. Soil texture is the relative proportions of sand, silt and clay particles. Sand particles are the largest (can be seen with the naked eye), silt particles are in between in size and clay particles are very small. The relative compositions of these three particles determines your soil texture class. If you wanted to determine your soil texture you can do a simple feel method to give you an idea. There is a link below on how to do this and an even more extensive link on soil texture from Colorado State.
https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/edu/?cid=nrcs142p2_054311
http://culter.colorado.edu/~kittel/SoilChar(&RibbonTest)_handout.pdf
Whether you have sand, silt or clay soil, will affect the size of the pores within the soil. Soil pores are the spaces between particles that hold water and oxygen. Sand, because it is a larger molecule, has large pores. Clay, because it is a smaller molecule, has tiny microscopic pores. The pores are where water or oxygen is available to the plants. Generally, sandy soils have larger pore size, hence they feel lighter when you are working with them. Larger pores hold less water and nutrients but have better aeration (more oxygen). This is typically appreciated as these soils usually have good drainage. Water that is applied rapidly moves through the topsoil and into the deeper layers. Clay soils, on the other hand, have very small microscopic pores. These pores hold water longer, hold onto nutrients but have limited aeration. This is why these soils are typically called heavy. Because these pores are very small, water cannot drain as well and clay soils typically have poor drainage.
The problem with mixing a small amount of sand into clay soil is that you create an even heavier soil than clay alone and it has even smaller pore sizes. This is because the large spaces between sand molecules are then filled with tiny clay particles. This results in a mixture that resembles concrete. In this mixture there is little to no water or oxygen available for plants to use and their roots may not be able to penetrate at all. You can avoid this problem by incorporating 50% sand into a clay soil, however that would mean removing half the topsoil in your garden and replacing it with sand, which is not recommended or practical. There is a great summary of the problem of adding sand to clay soils below. If you did need to improve your clay soil in some way, the recommendation would be to add organic material such as compost and mulch. The link below provides guidance on how to manage clay soil in the home garden.
https://s3.wp.wsu.edu/uploads/sites/403/2015/03/soil-amendments-2.pdf
https://vric.ucdavis.edu/pdf/soil_managingclay.pdf
So, given that information about adding sand to our native clay soils, you did ask about whether you could do that and put pavers in it. If you were creating a walking path, it might not matter to you if your soil underneath those pavers had poor texture and would not support the growth of plants. It is worth considering that development of this very heavy soil mixture, similar to concrete, under the pavers may lead to water runoff during heavy rain which then needs to be absorbed by adjacent areas. It also may limit the growth of larger perennial plants, such as trees and shrubs, in that vicinity depending on how much of their root zone would be affected.
In looking at the Contra Costa County Sandbag program website, there is no indication where the sand comes from. Therefore, I cannot be sure what its salt content is. Too much salt is not ideal for plants, but adding the sand to your native soil would already be detrimental to your garden. If you do choose to add the sand to your garden, you might call the city to see where they sourced the sand. Conversely, you could rinse the sand before using it and dispose of the water in an area separate from your garden in case it was excessively salty.
https://www.contracosta.ca.gov/5976/Sandbags
I hope this helps answer your questions. Happy Gardening!
Help Desk of the UC Master Gardener Program of Contra Costa County (SES)
Note: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ignore.edu/HortCoCo/ You can also subscribe to the Biog.
- Author: Pat Hitchcock and Jim Murphy, UC Master Gardeners of Napa
In a restricted area, such as an apartment complex or a small, confined yard, containers may be the ideal way to raise vegetables. Pot selection, container soil, container positioning, sunlight and heat deflection from walls or fences all contribute to a successful growing experience.
You can use many different kinds of containers, such as wooden planters, clay pots, plastic buckets or even plastic bags filled with planting mix. They must have drainage holes. If you are placing containers on a wooden surface, such as a deck, reduce the possibility of rot by raising the containers on small blocks to allow for air circulation.
Be sure your containers are deep enough for the crop you want to grow. Six to ten inches is sufficient for shallow-rooted plants like arugula, basil, chives, lettuce, green onions, radishes and mizuna. With a deeper pot, 10 to 15 inches, you can try carrots, celery, Chinese cabbage, garlic, leeks, Swiss chard and patio tomatoes.
Go for 18- to 24-inch-deep containers if you want to try beans, broccoli, kale, peas, peppers and short-vine (determinate) tomatoes. A container 20 inches in diameter and 18 inches deep will give you plenty of room for several small lettuces or for one pepper or tomato plant.
The planting medium needs to be both porous and moisture retentive. Because you may need to move your pots occasionally, it also needs to be lightweight. Garden soil is too dense and heavy. A good-quality potting soil will contain compost and nutrients for plants, plus vermiculite or perlite for drainage and peat or coir for holding moisture.
Finding the perfect place for your containers may be the most challenging part. Leafy vegetables such as lettuce need four to six hours of sunlight daily, but fruiting vegetables like peppers, beans and tomatoes need eight hours. An area near a wall that reflects sunlight can be too warm for some plants.
Container soil can get a lot warmer than the ground. Try shading the containers themselves if they are in a warm spot, while allowing the growing plants to get all the sunlight they need.
Container plants require more frequent watering than plants in the ground, and they also need more frequent fertilizing. Most commercial potting soils include fertilizer to get plants off to a good start. After six weeks or so, start fertilizing every other week with a half-strength liquid fertilizer formulated for vegetables or container plants. Nurseries sell organic and inorganic types. Check label directions for the suggested dilution, then double the recommended amount of water to get a half-strength solution.
For container gardens that are always on view, consider the many vegetables that are ornamental. Look for colorful versions of lettuce or Swiss chard, for example. A combination of leafy lettuces, blooming chives and a viola could produce an instant salad mix in a cool location. For the warm season, try a patio-type tomato with sweet basil at the base. Nurseries often have pots with such pre-planted combinations, but it's fun to create your own.
In April, the options for edibles are almost limitless. You can still start some cool-season vegetables, but it is also planting time for warm-season crops. The Napa Count Master Gardener website has several planting calendars in its “Healthy Garden Tips” section. Find that section under the “Gardening Resources” button on the left side of the home page.
Edible container gardens aren't limited to vegetables. Many perennial herbs do quite well in pots. Try thyme, oregano, marjoram and parsley. Edible flowers such as nasturtiums and violas also thrive in containers. Don't let lack of a garden plot keep you from the pleasure of harvesting your own edibles.
Tomato Plant Sale: U. C. Master Gardeners of Napa County will hold their fourth annual Tomato Sale and Education Day on Saturday, April 23, from 9 a.m. until sold out, in a new location at 1710 Soscol Avenue, Napa. Choose from 28 varieties, including heirlooms and new varieties in a range of colors. These healthy, Master Gardener-grown seedlings include types for fresh eating and for sauce.
Workshops: U. C. Master Gardeners of Napa County will hold a workshop on “Growing Tomatoes” on Sunday, April 10, from 2 p.m. to 4 p.m., at the Yountville Community Center, 6516 Washington Street, Yountville. The workshop will focus on techniques for a successful harvest, including soil temperature requirements; tomato types; care and fertilizing; support choices; and integrated pest management. Register with the Parks and Recreation Department at
707-944-8712 or on its web site.
The “Growing Tomatoes” workshop will repeat on Saturday, April 16, from 9:30 a.m. to 11:30 a.m., at the University of California Cooperative Extension office, 1710 Soscol Avenue, Napa. On-line registration (credit card only); Mail-in/Walk-in registration (cash or check only).
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.edu/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.
- Author: Michelle Leinfelder-Miles
I was speaking with a colleague a few weeks ago about field drainage in the Delta. Our conversation reminded me of a farm visit that I made a couple of years ago. I visited a corn field that was not growing well, and sections of the field had standing water. I consulted with UC Water Management Specialist Emeritus, Terry Prichard, on what this grower could do to improve drainage. I wondered about installing drainage tiles. The irrigation specialist did not recommend installing drainage tiles in the Delta. The high organic matter soils are so fine that the perforations in the tile just plug up. He also did not recommend a deep plow because some Delta soils have a layer of “blue clay.” It is not actually clay but it is anaerobic soil (which is what makes it blue) that has never been near the surface. The irrigation specialist had once visited a field that had been deep plowed and brought up blue clay. The field became completely unmanageable.
What the irrigation specialist did recommend was to dig 4-foot (deep) drain ditches. These would run parallel to the furrows and should be about 500 feet apart. These ditches would connect to another ditch that runs to the main drain of the island. These dimensions are not a prescription for all Delta sites, but they could give landowners a general guide for managing drainage, and in the case of the corn field I visited, make wet fields farmable. Each 4-foot ditch will result in about 10 feet of “wasted” (non-farmed) space, but having these ditches (and keeping them clean) is the only way to get the water out of the soil profile and off the field.
Before any effort is put into digging ditches, it would probably be beneficial, particularly for new landowners, to see from an internet mapping interface if there are any lines in their fields that would indicate past ditches or different soil types. If previous landowners leveled the land, they may have filled in drainage ditches.
Help for the Home Gardener from the CCMG Help Desk
Client's Question:
“I am thinking about what to plant in a strip along our concrete driveway and a fence line. I am wondering about a cactus garden. There is no watering source, other than by hand, which I am fine with and actually enjoy. Do you have any suggestions on types of cactus or plants? If cacti, I was thinking of ones that are not too spiny as I have small children as neighbors.”
CCMG Help Desk's Response:
Thank you for contacting the CCMG Help Desk about what to plant along your fence. It is difficult to give you specific suggestions without knowing what kind of sun exposure that strip gets. Walnut Creek gets quite warm in the summer and many plants that generally do well in full sun might not do as well between a fence and a concrete patio or driveway because both the fence and the concrete can increase the heat.
You also need to be careful about drainage, especially for succulents. Many succulent gardeners create a small mound (8-12” high) to plant the succulents on to assure good drainage. In your case, maybe that mound would be parallel to the fence. The reason: the soil in many parts of Contra Costa is clay, which does not offer good drainage, making it difficult to grow succulents in the ground. Many succulents grow well in containers where it's easier to give them a better soil mix and control the water. Although most succulents are drought-tolerant, prolonged periods without water may cause their leaves to lose color, shrivel or drop. Give plants just enough water to keep them plump and attractive. You might consider planters (maybe rectangular to fit the space). This could be a solution for you to consider.
Other possibilities for the space would be some of the drought-resistant grasses, perennials or smaller shrubs, either planted in the ground or in containers. Some suggestions for these include lavender, salvia (such as Salvia greggii--autumn sage), Origanum, Santolina, or “pink muhly”--a grass (Muhlenbergia capillaris).
Contra Costa Master Gardeners Help Desk
Editor's Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523.
We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/
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Whenever I encounter myths about gardening, I realize that I may be guilty of believing in some of them. As a Napa County Master Gardener, I've been trained to research information and to offer only science-based advice to home gardeners. So when I read something about gardening that sounds questionable, I always ask myself: fact or fiction?
Gardening myths and old wives' tales come from many sources. Even researching this article, I found that experts have differing opinions about the validity of many firmly held beliefs.
Myth: When you can sit on the ground comfortably with a bare bottom, it's time to sow seeds.
Truth: Taking the temperature of the soil before planting seeds or seedlings is important. For most vegetables, the soil should be between 55°F and 60°F when measured three inches deep. This warm soil helps roots to grow. But before the invention of soil thermometers, how was a gardener to know? According to folklore, farmers used their bare posteriors or their elbows to test soil warmth.
Myth: Placing gravel or pot shards in the bottom of a container improves drainage.
Truth: For many years, I planted pots this way. But during my Master Gardener training, I saw an experiment that demonstrated that soils had to be saturated before moisture would go to the next level. Putting some plain newsprint or a fine weed block in the bottom of your pot will keep soil from falling out or slugs from moving in, but gravel or shards won't affect drainage.
Myth: For a plant to bear fruit, you must have both male and female types.
Truth: While that statement is true for some species, many plants and trees are self- pollinating. Tomatoes are a good example. The flowers contain both male and female parts and just need to be jostled a bit or buzzed by bees to move the pollen around. I usually shake the plants daily as I pass by.
Pomegranates and most varieties of Asian persimmons are also self-pollinating. For small gardens, that's an advantage because you need only one tree to get fruit. In contrast, sweet cherries and kiwis will not produce fruit unless you have both a male and a female plant. Some apple varieties may be listed as self-fruitful, but you'll get more fruit if you have a second variety to cross pollinate.
Most garden vegetables, including summer squash and pumpkins, produce both male and female flowers. Bees make sure the pollen gets spread around. If the spirit moves you, you can help the process along manually.
Myth: Clay pots are better for container plants than plastic pots.
Truth: It depends what's in the pot and whether you are conscientious about watering. Clay pots do not retain moisture as well as plastic pots, and they tend to wick moisture away from the roots. Clay also is heavier than plastic and more breakable. If you tend to forget to water, then plastic may be the better choice for you.
Myth: After pruning a tree, treat open wounds with a wound dressing.
Truth: University research shows that is it not necessary to put tar or other wound dressing on a pruned or injured tree. In fact, it may be counterproductive. The tree had the ability to heal itself. Using a dressing can delay the healing or even cover up plant diseases and make them worse. Do proper pruning cuts with clean sharp tools at the correct time of year for the tree and let them air dry and heal on their own.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners (http://napamg.ucanr.edu) 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 Garden Questions?
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