UC Master Gardeners, Santa Clara County, CA
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UC Master Gardeners, Santa Clara County, CA


Garden Help > Monthly Tips

Good nutrient balance makes healthy garden soils. It is beneficial to get soil tested by a state-certified laboratory. Below is a collection of our monthly tips that relate to garden soils.

Soil Tips

Bone Meal for Bulbs?

Bone meal has traditionally been used as a phosphorus source for flower bulbs, but you may want to reconsider. If your soil is healthy, you may not need it and you may be better off with a balanced fertilizer designed for bulbs or even nothing at all. The nutrient content of commercial bone meal is lower than in the past due to the cleaning process, and the bone smell may attract raccoons or dogs to dig up the bulbs.

Cover Crops

Fava beans growing at our McClellan Ranch project
Fava beans growing at our McClellan Ranch project
You may want to rest in the winter, but the soil life needs to remain active and protected and preferably weed-free. If you’re not planting vegetables or ornamentals in an area for a few months, try plants designed to feed the soil and the organisms that live in it. Cover crops are ideal for putting nutrients back into your soil and keeping weed growth to a minimum. Fava beans are the most popular cover crop in this area and can be seen in abundance in community gardens. Other common crops are clover, vetch, and bell beans. Different cover crops provide a variety of benefits. Beans and other members of the legume family fix nitrogen from the air and make it available in the soil and to plants. The roots also break up heavy clay soil and improve its structure. While fava beans are edible, they provide the most nitrogen to the soil if they are cut up and dug in while they are still in the flowering stage. 

More Information: Choosing and Using Cover Crops

Mulch Bare Soil Before Rains

Deep cracks in dry soil from drought, by Jack Kelly Clark, UC
Mulch isn’t just for the summer. Yes, it’s good for conserving soil moisture and keeping the ground cool, but it’s important in the rainy season too. Bare soil that’s open to rain, wind, and sun becomes compacted and hard. Rain tends to run off instead of getting absorbed. Compare a patch of bare soil with one that’s been deeply mulched, and you’ll see the difference. An organic mulch that slowly decomposes keeps the soil beneath it moist and loose, plus it will suppress the weeds that will be sprouting with the rains.

More information: Impact of Mulches

Organic Soil Amendments

After harvesting remaining summer crops, add amendments such as blood meal, alfalfa pellets or fish emulsion to replenish nitrogen in the soil. Add a layer of compost to all existing garden beds to provide needed nutrients for winter crops. Be sure to leave some areas of native soil for ground-nesting bees.

Potting Mix vs Planting Mix

Planting soil mix
Is there a difference between potting mix, potting soil, and planting mix? The best advice is to read the label. The terms for bagged mixes aren’t regulated, so they can vary by manufacturer. What’s important to know is that not all bagged mixes can be used in pots. Some are meant to be used as garden fill, amendment, or mulch, so they won’t provide the right water retention, drainage, or nutrients for container gardening.

For more information: Bagged Potting Mixes

Sheet Mulching - "Lose the Lawn"

An easy and environmentally friendly way to "lose the lawn" is to smother the grass and mulch at the same time. Place cardboard or several layers of newspaper over the area, overlapping by eight inches to keep weeds from finding openings. Wet the cardboard or newspaper, then cover it with 4-6 inches of compost, plant trimmings, or other mulch. Having wood chips on top will give it a neat appearance. The materials will gradually break down and improve the soil over time. New plants can be installed by cutting an X in the cardboard or newspaper and placing the plants right through the mulch. UC Davis Arboretum Horticulturist Stacey Parker's website shows you how it's done.

Soil Management - Compost vs Mulch

Many home gardeners are confused about the terms “compost” and “mulch;” frequently these terms are used interchangeably, but they are not really the same thing. Here is a Comparison of Soil and Mulch from UCCE.

Amend soil with compost to create soil that will retain water but still drain well enough for roots to have the air and water they need.

Benefits of compost
- Forms aggregate particles with clay
- Creates larger pore spaces for water & air
- Helps release nutrients from clay so that plant roots can absorb them
- Supports the soil foodweb by providing nutrients for the organisms
- Lowers pH somewhat.

Benefits of mulch
Mulch does not get worked into the soil. It sits on top of your irrigation system and helps:

- Control weeds
- Prevent erosion
- Preserve soil moisture
- Keep roots cool and moist

Soil Solarization

Soil solarization can be used to control diseases, nematodes and weeds by baking everything under plastic sheeting.The best time for solarization of soil is from June to August. Transparent or clear plastic is the best choice. Leave the soil covered for 4 –6 weeks. Refer to the UC Pest Note on Soil Solarization for Gardens & Landscapes.

Wet Soil

The clay soils which dominate our area are particularly susceptible to compaction, especially when they have received a lot of rain. These soils are characterized by small mineral particles. Hence squeezing out the air spaces makes it more difficult for plant roots and soil organisms to get the oxygen they need to flourish. Try to avoid walking on or using heavy equipment on soil that is wet. Digging in wet soil can also destroy the structure, breaking up useful soil aggregates and earthworm tunnels. Try to wait until the soil is moist, not wet or dry, for easiest tillage. If you must walk or stand on the soil, use a board to distribute your weight over a broader area. Mulch can also create a bit of a cushion and help minimize compaction.

Why You Should Test Your Soil

Before adding fertilizer or soil amendments to your garden, first find out what your soil really needs by conducting a soil test. Knowing your soil’s pH value is important in determining which plants will thrive or struggle in your soil. Understanding the levels of nitrogen, phosphorous, and potassium in your soil will tell you which nutrients are abundant and which are lacking. Don’t overfertilize – excess nutrients can pollute local waterways. Commercial soil testing labs provide the most thorough results, but several home kits can give you a good baseline. Test soon and be ready for spring planting.

Will Pine Needles Acidify My Soil?

Photo: Japanese red pine, SelecTree, California Polytechnic State University
The short answer is no; this is a common garden myth. While it’s true that pine needles are acidic when they drop from the tree, even a thick layer won’t make much difference in your soil pH. They break down naturally and the microbes (decomposers) in the soil neutralize them. In fact, pine needles are a good mulch material because they tend not to form a dense mat, they stay in place during heavy rain, and they take longer to break down than other organic mulches.
More Information: Ten Garden Myths

Winter Soil Health

Straw mulch in vegetable garden, by Jack Kelly Clark, UC
Straw mulch in vegetable garden, by Jack Kelly Clark, UC
Areas of the garden that are not actively planted still need protection to support soil life and prevent soil erosion. Cover crops are one option. Their roots break up the soil, and if they are legumes, like fava beans, they add essential nitrogen. Mulches hold in moisture, moderate soil temperature, and help prevent weeds from germinating. Unlike rocks and synthetic mulches, organic mulches like leaves, wood chips, or straw also slowly break down, beneficial soil organisms, and add nutrients to the soil. A top layer of an inch or two of compost will slowly work down into the soil, amending it with organic matter. Manure from herbivores can also be spread over the top of the soil. Even fresh manure, which could burn plants if applied directly, can be used over a bare area to decompose in place and be ready for the next planting season.

More Information: Keep Your Soil Healthy

Worm Composting

Worm compostingWorm composting also called vermiculture or vermicomposting is a convenient way to decompose kitchen waste and provide nutrient-rich soil amendments for your vegetable garden.

Here is a description for Getting Started.

The Santa Clara County Home Composting Education Program offers Worm Workshop classes.

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