October Q & A
by Michelle Le Strange, UC Master Gardener Advisor

Q. What exactly is soil?

A. Virtually all gardeners agree that understanding your soil is perhaps the most important aspect of gardening. Soil is merely small particles of rock mixed with air, water, and organic matter. Particle sizes called clay, silt, sand, and their combination within a soil determine the soil's texture. Particle size also affects pore size which affects water drainage, water retention, aeration, nutrient supply, and soil strength. All plant roots need air, water, and certain mineral nutrients to grow in soil.

Clay soils have microscopic size grains that are flat and fit snugly together. Pore spaces between grains for air and water are tiny, so when clay soils get wet, drainage is painfully slow and air supply to roots is small.

Sandy soils have larger, rounder grains that fit loosely together so that aeration is good and water drains through fast, sometimes too fast, taking plant nutrients along with the water. Nutrients cling to the surface of particles. Clay soils have more surface area than sandy soils, so they have more natural fertility.

The ideal soil is one with clay, sand, and intermediate size silt particles. Gardeners refer to these as loam soils. The particles are in the right proportion to maximize water drainage yet capitalize on water retention nutrient availability and air supply. There are sandy loams, clay loams, loam sands, and loamy clays. The more predominant one size of particle is in a soil, the less versatile that soil is for many crops and the more skill is needed to grow healthy plants.

Soil structure relates to how particles within a soil clump together. Except for sand, soil particles do not exist singularly in the soil. Soil clumps or aggregates are desirable because they increase porosity tremendously. Aggregates are formed by the natural weathering (aging) process of soils and by binding chemicals that result from decomposition of organic matter.

Most California valley soils average one percent organic matter (OM) by weight. Adding OM such as compost, manure, straw, etc., immediately improves aeration and drainage of clay soils because their larger particles wedge between the super small clay particles forming bigger and more air and water channels (porosity is increased). In sandy soils organic amendments help hold water and nutrients in the pore spaces, so the soil stays moist and holds dissolved nutrients longer (porosity is decreased).

As the organic amendment is decomposed by soil organisms, plant nutrients are released into the soil solution and the remainder becomes humus, a sticky soft material that continues to bind soil particles together and maintains porosity. In other words, more soil aggregates form and the soil structure is improved.

Q. The backyard of my new house is not landscaped. The soil is a heavy clay that cracks as it dries out. Is there anything I should do to prepare the ground before I plant a lawn or trees and shrubs?

A. Clay soils that crack excessively while drying are often called "adobe" soils. If they are very low in organic matter, they lose their structure, become compacted, and puddle severely.

When moist, clay soils should be dug with a spading fork rather than a shovel to minimize large clods.

To improve structure, add large amounts of organic matter (such as compost, leaf mold, manures, nitrogen fortified ground bark, peat moss, etc.) to the soil before planting. For dramatic results, rototill a volume equal to 25 to 50 percent of the total soil volume into the garden area.

If raw materials are used, such as fresh wood chips, straw, sawdust, rice hulls, or nutshells, then supplement the soil with nitrogen fertilizer for the first few years. Soil microorganisms need nitrogen to decompose raw products and will compete with plant roots for this element.

If drainage problems prove especially difficult or costly to fix, consider installing raised beds to accommodate most of your garden plantings. Fill a raised bed with good, well-aerated soil, making beds deep enough for root growth.

Q.What is an alkaline soil and how do you fix it?

A. Soils with pH 7.1 and higher are considered alkaline and are high in salts containing calcium, magnesium, and sodium. If soils are excessively high in sodium, they are termed "sodic."

High concentrations of these salts keep seeds from germinating, burn roots, stunt plant growth, and cause leaves to scorch. If sodium predominates, then further damage occurs to the soil. Aggregates are destroyed, pores collapse, and water infiltration problems intensify.

Salty soils can be fixed relatively easily with several applications of water providing drainage is good. Sufficient water must be passed through the soil to dissolve the excess salts and carry them through the root zone. If the problem is slight, about 12 inches of water will do the job. Sometimes 24 to 36 inches of water are needed for intermediate to severe salt problems.

Whether a soil is sandy or high in clay content has little to do with the amount of water needed, but it does affect how long it will take to get the job done.

Sodium soils are often amended with gypsum. Gypsum supplies calcium to displace the sodium. When applying dry gypsum, mix it thoroughly into the soil to the depth you need to reclaim. Then water thoroughly.

Give Your Garden a Makeover (October 26, 2000)
by Carolyn Carpino, UC Master Gardener

Have you ever watched those shows on TV when a designer makes a ho-hum room look like a showplace by just rearranging the furniture? Ever wonder why we can't do that ourselves?

I think we become house blind. After awhile, we just don't see our furniture and accessories anymore and can't imagine them any other way. A designer comes in and sees the possibilities in all our everyday items. They move things around, put stuff in the closet, take from other rooms and voila - a whole new look.

The same thing can happen in our gardens. After years of seeing our plants, we really don't notice them anymore. Overgrown landscapes completely cover the exterior of the house or mushroom into the driveway and eat up the front walk. It becomes a constant battle to keep them whacked back, and they never really look very good. I've noticed when people move into a new house, they have one year to make changes - after that they become house blind, too.

So strip off the blinders and really look at your garden. It can be greatly improved without spending one dime, just by using variations of the same methods the home designers use.

Transplant: Move your furniture! Sometimes a nice plant is simply wasted by being overwhelmed by other plants. Last year we needed a palm tree to replace a frost damaged one. We decided to move a palm we had that made little impact where it was planted in the landscape. It was actually a nicer palm than we could have bought, didn't cost us any additional money, and is a showstopper in its new position. The moral of the story? Try to use what you already have before buying anything new.

New plantings frequently place plants too close to the house or other structures. As the plant grows, it's obvious that the mature size of the plant was never taken into account and now you have a problem. People often feel there's nothing they can do about it.

Not true! Just because a plant has always been in one place doesn't mean it has to stay there. Done at the correct time (now through December), transplanting is very successful with all but sub-tropical plants. Wait to transplant palms and other frost-tender plants until early spring.

Transplanting small or young plants is easy because they have a fairly compact root ball. Older, more established trees and shrubs, however, have a much larger root system. To minimize damage, encourage a compact root ball and lessen transplant shock, root prune the plant first. Using a sharp spade or shovel, cut a circle around the tree the size of the root ball you want to move. Cut straight down the depth of the shovel with each thrust. Wait a month or two, dig the new hole, then dig up the root ball, which should be full of healthy new feeder roots. Replant at the same soil level and water well. We used this technique last fall to move a 5-year-old 8 foot tall crape myrtle with great success.

Divide: After a few years, many perennials can develop into huge unwieldy clumps that bloom poorly and are out of scale with your garden. Dig up the clump and divide it into several new plants. Replant these by spreading them through your garden. This will give you "repetition", a technique designers use to give your garden a pulled-together look.

Eliminate: Do you really need it? Decide if a planting arrangement is enhancing the area. Homeowners and landscapers alike are usually guilty of over planting. Plants are planted to make a garden look full initially. It may be time to take some out.

Do you have five trees crowded along your fence where three well-grown ones would actually look better? Take two out. Do you have a plant that is bug and disease bait and never really looks good? If it's not adding to the landscape, take it out. How about a plant that is a pruning nightmare, sprouting straggly arms as soon as you turn your back? Again, if it's too much trouble, doesn't look good, and you have no other place for it, get rid of it. You may be amazed to find how much better your landscape looks without it.

Expand Your Beds: Most people start with narrow beds hugging their house and fences. Sometimes when plants have grown too big for the bed, the answer isn't to shrink the plants but to expand the beds. Bigger beds means less care because leaves and other debris will drop into beds and not on the lawn. Since lawn is the most high maintenance plant imaginable, less lawn also means less care.

This fall, try using your imagination instead of your checkbook to give your garden a fresh new look. Move things around, split things up, and get rid of stuff to get a look the designers would be proud of!

October 12, 2000