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A blog by the UC Master Gardeners of Stanislaus County

UCANR: Protecting California's natural resources

What is subsoil and how does it help a garden?

Author: Dr. Anthony Fulford

Published on: December 5, 2022

Author sitting on park bench wearing green shirt and smiling.

This blog article is for readers who may have heard of subsoil, but don't really know what it is, or how it may or may not affect their gardening efforts.

What is subsoil?

There are several layers (also known as “horizons” to soil scientists) that can be found when we dig deeper and deeper down into the soil. We can imagine all the individual layers of a soil stacked one on top of the other like a layer cake, this is called the soil profile. The surface soil is the uppermost layer of the soil profile, and the one we are most familiar with, because this is where most of the action takes place. Soil mixing with tillage, compost and fertilizer application, irrigation, plant root growth, and animal activity (including microbes) are mainly concentrated within the soil's surface layer. Additionally, decomposition of plant and leaf litter occurs most rapidly in the surface soil, this eventually leads to the formation of new soil organic matter. In comparison, the subsurface soil, or subsoil, is composed of one or more soil layers that lie below the influence of surface soil activities. There is not a consistent depth at which every surface soil layer changes into the subsoil layer(s), rather the subsoil occurs at a different depth from place to place depending on numerous factors, including some of the factors mentioned previously. This is the reason why it is difficult to determine where the subsoil layer begins in the soil profile.

What does subsoil contain?

Graphic of soil horizons showing the surface, substratum, subsoil, and bedrock.

Subsoil is found deeper in the soil profile and does not directly experience a lot of the processes that occur in surface soil. As a result, the subsoil has less soil organic matter, less insect and animal activity, slower air and water movement, and a slower rate of decomposition compared to the surface soil layer. However, the subsoil underlies the surface soil and is indirectly influenced by the activities that occur at or near the soil surface. Therefore, the subsoil layer(s) has the excess fertilizer nutrients, herbicides, pesticides, and other dissolved salts that were lost from the surface soil due to heavy rainfall or irrigation. As surface soil begins to erode and age, the water moving into the subsoil can also have a lot of clay that accumulates in distinct regions of the subsoil.

What does subsoil look like?

Area of soil that's been removed to show layers.

In this photo, the subsoil layer is seen below the yellow mark on the measuring device, Anthony Fulford.

It is possible to identify subsoil by recording when and where you notice distinct changes in color, texture, and/or structure of the soil. The surface soil is often enriched in organic matter, giving it a dark appearance, typically dark brown or black. The movement of smaller soil particles from the surface soil into the subsoil increases clay content. The subsoil also lacks many of the rooting channels and biological pores that help build and support soil structure due to the limited presence of plant roots and animal activity. Therefore, as you dig deeper in the soil profile, if you see the soil color begin to fade from a dark brown or black to lighter shades of gray or brown, you notice it becomes harder to dig deeper into the soil, and/or you notice the soil is no longer loose and crumbly but becomes denser and lacks plant roots and worm channels, it is very likely you have reached the subsoil layer.

What is subsoil used for?

In general, the subsoil is a less suitable medium for plant growth compared to surface soil because of some of the factors mentioned previously. There are properties of subsoil however that make it suitable for other uses such as a source of “fill soil” for “cut-and-fill” construction operations, as a source of clay for building materials, and as an absorption layer for on-site wastewater disposal.

What can home gardeners do to keep their subsoil in great shape year after year?

A piece of soil showing the gradation of subsoil, Anthony Fulford.

Healthy soils are effectively balanced among the chemical, physical, and biological processes that allow soil to function properly and achieve a desired outcome, such as being an optimal medium for plant growth. Therefore, to build or support healthy subsoil, it is important to consider each of these processes, keeping in mind that what occurs in the surface soil layer can, at some point, be reflected by what is observed in the subsoil. With this in mind, to encourage soil health in the subsoil it is important to recognize that certain plant nutrients move with rainfall or irrigation water, such as nitrogen, and may be enriched in the subsoil. Effectively balancing plant nutrient fertilization to avoid excesses can limit the amount of plant nutrients transferred from the surface to the subsoil. The subsoil often has a poorly developed structure due to the lack of plant rooting channels and animal activity (including microbes). Growing a diverse group of plants that have distinctly different rooting depths, ranging from shallow- to deep-rooted, can encourage the formation of rooting channels that extend into the subsoil. The burrowing activity of earthworms also creates channels that deep-rooted plants can easily use and follow into the subsoil. Additionally, the presence of actively growing plant roots acts as a food source in the subsoil that stimulates microbes. The physical structure of subsoil can be improved with deep-rooted annual or perennial plants. As soil structure improves and more of these biological pore spaces are created, the rate of water and air movement into the subsoil layer will increase, helping sustain the balance among chemical, physical, and biological processes.

What is the substratum layer of soil? Does that layer affect gardening at all, and if so how?

Plants of varying heights growing in a brick planter.

Growing plants with different rooting depths encourages rooting channels into the subsoil, Ellen Zagory.

Stratum is a term that is commonly used to identify a distinct layer of rock or soil. Substratum then is a term used to indicate the relative underlying position of a distinct rock layer within stratified rock formations or a distinct layer of soil that lies below the surface soil. The substratum layer of soil has some of the same properties that are common to the subsoil. Although, many of the chemical, physical, and biological processes are further diminished in the substratum layer compared to the subsoil. Specifically, growing roots are not likely to be found in the substratum, so the properties of the substratum layer are unlikely to directly influence plant growth. The limited amount of water and air in the substratum layer will however help breakdown larger solid rock fragments, forming a loose and very coarse structure that closely resembles the mineral composition of the underlying layer(s) of the soil profile.

What is the bedrock layer? Does that layer affect gardening at all, and if so how?

Bedrock is the bottom layer of the soil profile layer cake. The bedrock layer consists of solid rock that has not yet been exposed to the chemical, physical, and biological processes of the surface soil and subsoil. In some places, bedrock is the foundation from which the overlying soil layers developed, while in other places, the bedrock layer may have become “buried” by windblown sand or sediment. Bedrock does not directly influence plant growth, but it can determine the type of clay minerals found in different layers of the soil profile.

Dr. Anthony Fulford is the Area Nutrient Management and Soil Quality Advisor for Stanislaus, Merced, and San Joaquin Counties.

Public Value: UCANR: Protecting California's natural resources

Focus Area Tags: Environment

Tags: biological processes (1), chemical (1), healthy (1), herbicides (2), irrigation (6), nutrients (2), organic matter (1), pesticides (11), physical (1), rainfall (1), roots (5), soil (6), structure (1), subsoil (1), texture (1), tilth (1), water (17), worm (1)

Comments: 0

UCANR: Promoting healthy people and communities

Does your garden soil need testing?

Author: Ed Perry
Editor: Anne Schellman

Published on: December 20, 2021

Handful of soil (pixabay.com)

Gardeners sometimes call the Master Gardener help line asking if a soil test is necessary before planting a home garden. For most people, the answer is usually no. In some cases, soil analysis can help identify an unusual problem, such as excess soil salts or minor element deficiencies. If you are worried about lead contamination, a soil test is a good idea.

To have your soil analyzed, contact a commercial testing laboratory. For a list of soil laboratories located in Stanislaus, Merced, Fresno, and Merced Counties, visit https://cemerced.ucanr.edu/ClimateSmartAg/HSP/SoilTest/Soil_Testing_Laboratories_in_Fresno_Madera_Merced_and_Stanislaus_Counties/

Vegetable Gardens

For vegetable gardens, the application of a fertilizer containing nitrogen and phosphorus is usually all your soil will need to get your vegetables off to a strong start. Other nutrients like zinc or iron are sometimes deficient or unavailable in certain soils, but they are usually not applied unless plant deficiency symptoms appear.

Diagnosing a Plant Problem

Man holding soil in his hands and smiling.

Master Gardener Mike James learning about soil testing during the 2020 training in January.

When a plant grows poorly, people often feel some nutrient deficiency in their soil is responsible. However, plant symptoms such as stunted growth, abnormal leaf color, poor fruit production, leaf drop, or twig dieback may also be caused by other factors which affect plant growth. An inadequate supply of soil moisture in a plant's root zone will restrict its growth. Simply wetting the soil surface won't supply a plant with enough moisture; deep, thorough irrigations are necessary.

Besides moisture, oxygen is also required in the soil for good root growth. Poorly drained soils often have little oxygen in them because excess water fills all the spaces between the soil particles. My advice to gardeners is to correct drainage problems first, then worry about fertilizers. Often problems with sick and dying plants are caused by overwatering or a lack of good soil drainage than by nutrient deficiencies.

If you have an unhealthy plant, gently dig near the root system and check soil moisture and drainage. Since plant roots need oxygen, roots may suffocate if excess water does not drain quickly. Unfavorable climatic conditions, including temperature extremes and drying winds can also affect plant growth, as well as insect pests and diseases. For small plants, pull up a plant or two and check to see if the roots are healthy.

The best way to keep soil healthy, especially in vegetable gardens is to add compost annually to improve soil health. For perennial crops like fruit trees, annual applications of fruit tree fertilizer in spring can be beneficial.

The UCCE Stanislaus County Master Gardeners Can Help!

If you need help diagnosing a plant problem, take a plant sample to the UCCE office located at 3800 Cornucopia Way Ste A in Modesto. Master Gardeners are available on Wednesdays from 9:00 a.m. to noon in person or by phone (209) 525-6802. You can drop off a sample anytime during business hours or fill out an online survey and attach photos using this link http://ucanr.edu/ask/ucmgstanislaus A Master Gardener will get back to you within 5 days of your request.

If you live in another county in California, you can find your local Master Gardener program by using this link https://mg.ucanr.edu/FindUs/

Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.

Public Value: UCANR: Promoting healthy people and communities

Focus Area Tags: Yard & Garden

Tags: fertilizer (2), garden (26), master gardeners (119), roots (5), soil (6), stanislaus county (70), test (1), vegetable (5)

Comments: 2

UCANR: Safeguarding abundant and healthy food for all Californians

Planning and Prepping for Your Spring Garden

Author: Terry Pellegrini

Published on: January 11, 2021

It's a cold winter's day here in the Central Valley. But instead of curling up in a cozy chair with a cup of tea, I'm out in my garden, planning and prepping for my spring planting. For me, this is the fun part, walking the gardens, looking at the raised beds, empty pots, and bare earth. I imagine what I'll place where, and jot down what needs to be done to prepare these spaces. Then it's inside to peruse the seed catalogs and online sites, make notes, and dream about the coming spring.

Planning your garden now, I feel, will save you headaches and money, come spring. By taking the time to understand how much space you have (or don't have), whether or not you wish to plant directly in ground or containers, or a combination thereof, and what types of plants grow best in your area, you'll only purchase what you need. In addition, you can decide whether or not you wish to devote the time to starting your seeds indoors or in a greenhouse, plant the seeds directly in the garden beds, or if transplants are the way you wish to go.

Raised bed preparation. (T. Pellegrini)

Some other things you'll need to take into consideration when planning your spring garden is how much sun you have in each of the proposed planting areas. If uncertain, take a look at the surroundings now. While you'll not be able to gage precisely how much sun they'll have come spring and summer, you can take note of things that could possibly shade them or hinder the sun from reaching them. Are there a lot of trees in the area that will shade them once their leaves have returned? Will that patio cover keep the sun from reaching them? Perhaps the arbor next to the west bed will be covered in greenery when the Wisteria blooms, blocking out the sun. If you are contemplating shade plants, are there locations that may be too sunny for them? Taking the time to scope out the positioning for your new plants will give them the best chance to grow and thrive.

If you are thinking of planting spring veggies, take under consideration what you and your family will actually eat. If the kids detest string beans, then planting a huge area full of them is probably not a good use of the space, your time, or money. However, if zucchini is something you eat frequently, then two mounds may serve you better than one.

Make sure your garden beds aren't shaded by nearby trees. (T. Pellegrini)

Winter is the best time to prepare your planting areas for your spring garden. Whether you are planting flowers, or veggies, in raised beds, containers, or in ground, getting your soil ready now is key. The time you spend this winter prepping and amending means that you'll be able to plant immediately once the threat of frost has passed (usually around mid-March here.) In addition, placing amendments, such as steer or chicken manures, in your garden now will give them a chance to “mellow” and break down, so that the soil is ready for transplants and/or seeds.

Now is also a good time to get control of any weeds in your proposed planting areas. Removing any weeds now, before the weather gets warmer and they decide to seed, means less work for you come spring and summer. I like to get down, move the soil with a trowel, and pull out any stray roots or seeds that I see. You may even find grubs and larvae of Hoplia beetles that you can remove, saving your precious roses and flowers this spring.

Many of us reuse our favorite pots and containers year after year. As such, these pots will need some TLC and prep as well. All the old soil will need to be removed and the pot cleaned with a solution of one-part bleach to nine parts water. Submerge in solution and soak for at least 10 minutes. This sterilizes them, removing any insects or diseases from the previous plant in the pot.

Planning and prepping your garden now for your spring planting will give you that head start to a successful, satisfying, and fun gardening adventure. So, get out your seed catalogs, notebook, and take a walk in your yard or garden space, and imagine all the possibilities. Happy Gardening!

Public Value: UCANR: Safeguarding abundant and healthy food for all Californians

Focus Area Tags: Pest Management, Yard & Garden

Tags: Central Valley (6), frost (4), gardening (52), Pellegrini (5), pests (24), planting (5), preparation (1), soil (6), spring (9), vegetables (35), winter (8)

Comments: 3

UCANR: Promoting healthy people and communities

Sustainable landscaping can garner big results and savings!

Author: Rho Yare

Published on: October 22, 2020

For those of us who have lived in Stanislaus County for many years, can you remember what life was like when there were no water meters, and we paid a flat fee for water? Now, those of you who did not live here at this time or were too young to remember those wild water using days, let me tell you what it was like. In a few words, great, incredible, affordable. You could use all the water you wanted, no timed showers, no restrictions to only doing full loads of laundry, and no sprinkler rules or regulations at all! A person could water the sidewalk all day long and never have any consequence. We lived the water wasting life.

And then, one day cities began reading those water meters and charging the nice, water loving citizens by the units of water used each month. You could almost tell the day the bills arrived. Neighbors discussed them at the mailbox with anger, frustration, even fear. “How can I afford this every month?” Or “How can I reduce my monthly bill?” And that was the birth (or at least the beginning) of serious discussions about how to be “water wise” or how to conserve water to lower the units of water consumption that consequently will lower the monthly bill.

Lavender, deergrass, and Aster 'Purple Dome'. (Ellen Zagory.)

One of the big consumers of water for most homeowners is the yard. That lush green expanse of grass is a water “hog.” Yes, not only does the lawn require feeding, mowing, and often insecticides and/or fungicides to keep it looking and remaining at its best, it takes water - and gallons of it in the hot months. Lawns are great for kids and dogs, but if you aren't using it, maybe it's time to rethink your landscape.

During this last drought, many people just stopped watering their lawn. This helped reduce their water bill but does little else. In many cases it killed street trees as well.

Not watering grass in our climate guarantees that the grass will die. In its place, however will be weeds. Weeds can live and multiply in harsh, waterless conditions. And all those weeds are spreading seeds that land in your neighbor's lawns. And eventually even the weeds die from normal life cycle or lack of water. Then the wind blows the precious topsoil from your yard. This topsoil mixes with the other air in our valley and adds to air pollution.

What if I want to keep my lawn?
There are a few things you can do if you do not want to give up your lawn completely. Think about reducing the amount of lawn in your yard, which can help you save water and money. Having a beautiful yard without green grass does not mean just rocks, cactus, or artificial turf. Begin by removing a small section of the grass. Check with the Stanislaus Master Gardeners and local nurseries for plant suggestions to replace that green grass with other green, or gray, or yellow plants. Think beyond bark, boulders, and bare ground. The possibilities are endless. This time of the year is a perfect time to begin making plans for that winter yard renovation!

Butterfly bush, salvia, CA fuchsia. (Ellen Zagory)

Discuss your ideas with a garden professional at your favorite nursery or contact the Master Gardeners for some advice and on-line information. Please remember that the first year of a plant, shrub, tree, or anything you add to your yard will require regular and proper watering until established. The water bill may not change much the first year, but over time you will see the savings.

What are some easy tips to save water?
Now, if you are not ready to commit to a grassless or partially grassless yard there are some changes that can help in reducing water consumption. First, examine your current watering system. If you have a sprinkler system, do not assume that it is working properly. Checking weekly during the warm weather is a must, especially after the lawn is mowed and in the daylight. Is everything working properly, sprinklers putting water on the lawn not the sidewalk or street? Are the sprinklers clogged, broken, or even missing? If you have an automatic timer, check the timer, and remember to decrease time and days as the daylight time shortens and weather cools, and turn the sprinklers off when the rains begin. Be an agent of change for the better! Making a few changes now can make a difference in your water bill, landscape, and our world because we are all in it together.

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Join Rho Yare on Zoom for an evening of tips on how to reduce your water bill, yard work, pesticide use, all while having a gorgeous yard on Tuesday, October 27, 2020 from 6:00-7:30 p.m. Sign up at http://ucanr.edu/sustainable/2020 to receive your link.

Public Value: UCANR: Promoting healthy people and communities

Focus Area Tags: Yard & Garden

Tags: affordable (1), grass (1), pesticide (3), pollution (1), saving (9), soil (6), sprinkler (1), Stanislaus County (70), sustainable landscaping (1), water (17), water bill (1), Yare (3)

Comments: 1

Summer and Fall Events 2019

Author: Anne E Schellman

Published on: September 2, 2019

Summer and Fall Events, 2019

Ready to learn about local pollinators and how to welcome them to your garden? Take our Attracting Pollinators to your Backyard class this Thursday, September 5, 2019 from 6:00-7:30 p.m. USDA Scientist Kathryn Prince will introduce common native pollinator bees and butterflies found in our area and which plants they prefer. You'll also receive free milkweed and other wildflower seeds! Voluntary $2 donation asked. Sign up at ucanr.edu/pollinators/2019

Showy milkweed plants and a monarch butterfly. (Xerces Society)

Seed Saving Workshop Sept 19
Join us Thursday, September 19, 2019 from 6:00-7:30 p.m. for a fun evening on saving vegetable seeds. Learn which seeds can be saved and how best to save them. There will be a hands-on portion, and afterwards you'll take home a mason jar full of heirloom tomato seeds, as well as seed packets of other heirloom vegetables. Cost is $5. Sign ups coming soon!

Vegetable Gardening for Absolute Beginners Oct 17
You asked, we answered! Several community residents reached out to us requesting a class about the “basics” of vegetable gardening. Comments included wanting to learn more about:

How to identify your soil type
How often to water and why
Making your garden water efficient
Which vegetables to plant and when

This free class will be held on a Thursday evening from 6:00-7:30 p.m. Participants will receive free a set of cool and warm season vegetable seeds.

Succulent Gardening Workshop Oct 26
Curious to know more about succulents? On Saturday, October 26, 2019 we're holding a morning workshop all about these colorful plants! You'll learn about different varieties and how to grow and propagate them. We'll also design a succulent garden box together. You'll take home plenty of cuttings to decorate your landscape!

Stay tuned for more information. This workshop is limited to 30 participants, so make sure to sign up as soon as you see it advertised to hold your space!

Never miss an event!
Follow us on Facebook or twitter @ucmgstanislaus or visit our event Classes and Workshops page regularly.

These four events will be held at the Agricultural Center in Modesto in Harvest Hall in rooms D&E.

Focus Area: Yard & Garden

Focus Area Tags: Yard & Garden

Tags: bees (13), butterflies (12), garden (26), gardening (52), plants (25), pollinators (28), soil (6), succulents (7), USDA (1), vegetables (35)

Comments: 0

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