Soil Amendments
Pre planting vs. Post Planting
options for improving soil
Soil Amendments
• Are chemical and organic material additives that are
used to improve specific soil characteristics
• Usually added when the landscape is bare (pre planting)
and the soil can be best mixed thoroughly to incorporate
amendments evenly
• Best done at the recommendations of a soils report
taken at the site before planting in the design phase
• After planting soil amendments other than organic
composts, fertilizers, and mulches are rarely used
Soil Amendments
Sulfur
Used to lower soil pH (Make it more more acidic)
Lime - used to raise pH
Not a common So. Cal Problem
Improve soil structure
Aggregate heavy soils
Reclaim salty soils
pH of Most Southern California
Soils
• Typically Southern California along with
most Western soils are at neutral to high
pH levels.
• This is due to the original parent rock
characteristics and the lack of substantial
rainfall west of the Rocky Mountains
• Rainfall is slightly acidic and lowers the pH
East of the Rockies with regular rainfall
Texture of most Southern California
Soils
• Soil texture is the relative %’s of the 3
different soil separates within a soil.
Soil Separates
• Sand
• Silt
• Clay
Texture Characteristics
• Sandy Soils – Gritty to the touch. Fast draining,
Lighter in color, Lower in nutrients, Typically
lower in organic material. Good for plants
needing good drainage.
• Silty Soils – Smooth and silky to the touch.
Drains well unless completely dried out, holds
moisture and nutrients better than Sandy soils do.
• Clayey Soils – Sticky to the touch when wet.
Darker in color, Hard to work in. Fertile, easily
compacted when wet
How Can We Tell What Type
of Soil We Have?
We can use a soil probe to see the soil conditions
down to the root zone of the plant material.
This will serves well in diagnostics with plant
problems that often result from root problenms
We can touch the soil
When you touch a bit of moist
soil….. Is it
Sticky?
Silky?
Or
Grainy?
Can you make a
ribbon with it?
The one thing we can do to
improve soils no matter the texture
• Add organic material to the soil either by
cultivating in organic compost when open
and free from established plantings, or by
ensuring a regular supply of organic
material by covering the soil with a regular
blanket of mulch (Post planting).
Do No Harm to the Soil with
Common Landscape Maintenance
Equipment
Proper training is
essential
Blow leaves back into the beds and grass clippings
back on the lawn (within reason) when cleaning of
the hardscapes so this material can be incorporated
back into the soil
Composted
Organic Composts
Un composted
Buying in bulk
Insure organic
amendments are
composted
Humus creates the black color in
most composts and soils
Bagged organic compost
Redwood compost
Is a byproduct of the
lumber industry and
tends to last longer in
the soil
Adding Organic Composts
• To existing planted areas remember that the
smaller the particle size of the compost the more
important incorporating it into the existing soil
becomes
• Hard to do this around planted beds without
disturbing the root systems of existing plant
material
• Most commonly done in annual flower beds
where the plant material is changed out one or
more times in a year.
Annual Flower Bed – Color Changes
Usually at major entrances, along borders, or focal
points in the Landscape
Can be changed 2-4 times per year
Since most of the older material is removed when
changes are made the soil can be easily amended
with each color change.
Bedding color responds well to a slow
release complete fertilizer like
Osmocote 14-14-14 that can be applied
after planting
Bedding color is used in multiple applications in the landscape
Types of Annual Color - Fall into Winter
• Pansys
• English Primrose
Winter
Iceland Poppies
Spring into Summer
Early Spring ranunculus
Late Spring and through Summer Impatiens
Summer Annuals
Bedding begonias
Vinca
Bark Mulches
Although very
Attractive many of the
pieces of these Bark
mulches will not
decompose for over
10 years and in a
severe rain storm may
easily float and even
easily wash away
Shredded Bark Mulch
This is the preferred mulch for soil rejuvenation and protection
These pieces will last years
Shredded Bark
Mulch
These pieces will last months
The diversity of size particles is the key to
slow incorporation into the soil matrix and
success as a weed barrier.
http://www.aguinagagreen.com/ground-cover---mulch.html
Bulk Organic Compost
Turning bulk organic compost
Organic Mulches
Vegetable dye colored mulch
Cocoa mulch
Compost vs. Mulch
• Organic Compost is usually fine textured
with small particle sizes less than a half of
an inch that feels fluffy and rich to the
touch. Compost must be incorporated into
the soil
• Mulch is much larger 2-6” in particle size
and “shreddy” in texture. Mulch is laid in a
blanket over the soil to a depth of 4” and
kept to a depth of 2-4” over time
Benefits of Shredded Bark
Mulches
1. Saves Water by reducing evaporation from the
top of the soil = Cost savings to client
2. Cools Soil – Allows for feeder roots to work up
closer to the top of the soil with more oxygen
and nutrient accessibility
3. Increases Bio Activity – Brings back Bio
activity of the soil like earthworms, mycorrhizae,
4. Helps Control Weeds. Insect weed seeds wont
germinate through a layer of 2-4” of mulch
Around Tree Root Crowns
Into and around Planting beds
Mulch needs to be kept at between 2”- 4” to
be effective as a weed barrier and to allow for
effective water percolation down into the soil
below
Blowing mulch in through a large
hose for large areas
Inorganic Mulches
Tumbled glass mulch
All inorganic
mulches need an
underlayment of a
filter cloth as a weed
barrier
Mulch
from
colorized
recycled
tires
Stone mulch
Lava rock
mulch
Colored Glass Mulches
Naturally colored
small stones or
pea gravels seem
to have the best all
around natural
look. They work
especially well for
cactus and
succulents
gardens and as a
top dressing for
containers to give
them a finished
look.