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: Ben Faber
Psyllids as a pest group have very few specific predators that can be used in biocontrol. Instead there can be some control by generalist predators, like minute pirate bugs, spiders, lady bug beetles and predatory thrips. Predation, though, does not completely remove the pest, in this case Asian Citrus Psyllid. Leaving a few infected ACP to spread the HLB bacteria to trees, though, is a major problem because tree infection only requires a small amount of bacteria to eventually cause tree death.
Chemical control is being used in most situations for major control of the insect, and thereby the spread of any insects infected with the bacteria causing Huanglongbing. It turns out that pesticides that supplement more traditional modes of action can also be used. Kaolin is a white nonabrasive fine-grained mineral that when is sprayed on the plants forming a particle film. This compound is well known to suppress several species of insects in different crops due to host selection interference.
A recent study in Brazil investigated the influence of two kaolin formulations on the landing and feeding behavior of ACP. Both kaolin formulations had a repellent effect and interfered with the feeding behavior of ACP on citrus. Kaolin reduced the number of psyllids and protected the citrus plants from insect feeding. Frequent spray applications on the border of the farm could be an important strategy to reduce HLB spread. Spraying to control ACP spread on orchard border trees is often critical because this is where infestations often start. Kaolin won't be a replacement for other pesticide sprays, but could be an added tool for controlling the pest and spread of the disease - another integrated management tool.
Spray application of different kaolin formulations on sweet orange plants disrupt the settling and probing behavior of Diaphorina citri
M. Miranda1, O. Zanardi1; H. Volpe1; R. Garcia1; N. Roda2, E. Prado3
1 Fundecitrus, Araraquara, Brazil, 2 Tessenderlo Kerley, Inc./NovaSource, Phoenix, USA, 3 Universidade Federal de Lavras, Lavras, Brazil
http://www.icc2016.com/images/icc2016/downloads/Abstract_Book_ICC_2016.pdf
Photo: Kaolin spray on Citrus Leaf
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program Contra Costa County
Gardener's Request: I'm a new homeowner with a garden with clay soil apparently and trees that are now dropping leaves. How do I garden with clay soil and what should I do with the dropping tree leaves – use them in the gardening and how or disposing of them in my green bin?
MGCC's Help Desk Response: Thank you for contacting the UC Master Gardeners Program's Help Desk with your questions about gardening in clay soil, and whether to remove leaves from the landscape or incorporate them into the existing soil.
First, about gardening in your clay soil:
Your clay is made up of air, water, organic materials, and minerals. The balance of these ingredients determines your soil type. Clay soils are those that are often rich with nutrients, and renowned for their water retention capabilities, but can become compacted over time, creating a less hospitable environment for plants. This link provides information from UC Davis discussing how to work with your clay soil to get the best results. http://vric.ucdavis.edu/pdf/soil_managingclay.pdf
One of the most essential components to gardening in clay soil is creating good tilth (i.e., ability to grow plants, especially from seed). This is accomplished by carefully adding organic matter such as manure, compost, and/or planting cover crops to your existing soil. This article by a Marin County master gardener discusses the many ways that you can improve the tilth of a clay soil with organic matter. http://www.marinij.com/article/NO/20160304/FEATURES/160309921
Use of fallen tree leaves in the garden:
Thank you for submitting your questions, and I wish you luck in your gardening decisions.
Help Desk of the UC Master Gardeners Program of Contra Costa (JJM)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins 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, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
When clients bring sickly plants to the Master Gardener help desk, we ask about conditions in their garden. How often do they water and what method do they use?
For every inch a plant grows, there is probably an inch of roots holding it in the ground and nourishing it. In my experience, clients often water less than plants need. Ten minutes with a drip system three times a week is usually not enough.
When I was training to become a Master Gardener, our class studied how fast water drains through soil. Dry soil has tension; water moves around the surface until it can work its way into the soil. For a demonstration in class, several large tubes were filled with different soil types: sand, mulch, clay, loam and gravel. We watched water work its way down through each soil type and learned that each level had to be saturated before the water moved to the next level.
The same is true in your soil. For deep roots, water deeply.
Many vegetables develop roots that go three feet deep; several, like tomatoes, can have four-foot-deep root zones. Consequently, that is where the water needs to go.
Last year, Napa County Master Gardener Ray Sittig made drainage slits in gallon-size cans, then sunk a can in the soil alongside each of his tomatoes. He filled the cans with water twice a week, and the water slowly seeped into the soil.
Hardpan is another potential problem. Your soil's hardpan is the layer below the topsoil that is impervious to water. In my garden, it is a couple of feet beneath the surface. Hardpan was formed by clay deposited during flooding. Most of the top couple of feet of soil has had mulch, compost, fertilizer and other amendments added. Water penetrates easily but stops when it reaches the hardpan. I often push a length of rebar into the soil to see how deep it goes before hitting hardpan. In my vegetable garden, I continue watering until the rebar goes in easily.
When preparing to build raised beds, some gardeners dig the soil below the bed and work compost into the soil to break up the hardpan. Then the raised bed with its improved soil is built on top.
When I plant tomatoes, I place plastic on top of the soil to conserve water. This barrier keeps moisture in the soil, warms the soil and encourages growth. I have also used clean cardboard, cutting holes in it for the vegetable seedlings.
After planting, apply mulch to the soil surface to retain moisture. My habitat garden, which I don't irrigate, has a heavy layer of mulch. Because of that moisture-retaining barrier, it is still easy to pull weeds. One reason to remove weeds is to keep them from taking water from the plants you want.
If you have a plant problem, bring it to the Master Gardener help desk (see hours below). During the summer season, Master Gardeners also staff a help desk at farmers' markets and garden centers around Napa County. Please bring your plant sample in a plastic bag.
Workshop: Napa County Master Gardeners will hold a workshop on “What's Bugging You?” on Saturday, June 18, from 9:30 a.m. to 11:30 a.m., at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Understanding pests and blights that affect your vegetables is key to managing them. Squash that doesn't grow, tomatoes with peculiar markings, artichokes full of earwigs, plants that fail to thrive − all these and more will be discussed. Bring your own problems to show and tell and learn how Integrated Pest Management techniques can help. Mail-in/Walk-in registration (cash or check only). On-line registration coming soon.
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: Ben Faber
Water moves in a wetting front. When irrigation water hits the soil it moves down with the pull of gravity and to the side according to the pull of soil particles (more lateral with more clay). Soil is a jumble of different sized soil particles, from clay to silt to sand sizes and then often intermixed with stones of different sizes from gravels to boulder. The different textures determine how water moves. It moves fastest through coarse textures and slowest through finer ones – the clays, the ones with the smallest pores. But soils are a jumble of particle sizes and pores.
Water first moves down the larger pores and then it slowly moves through the larger ones. As water moves through the soil it carries salts that have accumulated in the soil. At the wetting front is where the salt accumulate. As the water moves through the larger pores, salts migrate/diffuse from the small pores to the larger ones. This diffusion takes a bit of time, so typically the small pores have a larger salt concentration than the larger ones.
So an initial application of water will carry the salts from these large pores and if the irrigator were to stop in mid-application, it allows time for the salts to move out of the small pores into the larger ones. Then when the irrigation recommences, it will carry more of the salts out of the wetted area – the root zone. This technique is called “bumping” where an irrigation is stopped and then restarted in order to improve not only leaching, but also reduce runoff.
This principle also is at play when there are two or more sources of water quality. Soil salinity can be no lower than the irrigation water that is applied. Then as the soil water is removed through plant absorption or evaporation, the salinity increases. The soil salinity can easily be two to three times higher than the irrigation water.
If there are two sources of water, the initial application can be with the poorer quality water, and once that has reduced the soil salinity, then the better water quality can be applied which will then bring the soil salinity closer to that of the better quality water. By doing this two part leaching, the amount applied of the better quality water can be significantly reduced. This is a type of “bumping” to improve leaching.
Watch this U-Tube video on how water moves through soil, thanks to the work at Walla Walla Community College.
https://www.youtube.com/watch?feature=player_detailpage&v=J729VzBeI_g
Thank you Walla Walla Community College for the video