Manual of California Native Plants

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Soil amendments and Mulch

It is helpful to know where the plant grows naturally.

Riparian plants like moisture. Some tolerate mulch, but the real water lovers do not.
Most of the non-native plants that provide color fit here.

Examples of riparian plants that are only moisture driven include (don't like mulch):

Anemopsis californica

Yerba Mansa.

Carex

Sedge.

Heleocharis macrostachya

Spike Rush.

Juncus

Rush

Mimulus guttatus

Seep Monkey Flower

Scirpus

Bulrush.

Typha domingensis

Tule

Riparian edge plants tolerate or even like soil amending.

These plants have adapted to seasonal flooding and soil buildup. The deer and antelope give the area extra nutrition when they come down for a drink and forage on the creekside plants. The creek, pond, river or lake provides a continual source of moisture. Mulch in the form of tree litter commonly builds up on the banks in this riparian corridor. Most of the non-native shrubs and trees that are in your local garden center fit here. Fruit trees also fit here.

Examples of riparian corridor plants that need moisture but tolerate mulch.

Acer macrophyllum

Big Leaf Maple.

Aesculus californica

Buckeye.

Carpenteria californica

Bush Anemone.

Calycanthus occidentalis

Spice Bush.

Cephalanthus occidentalis californica

Fraxinus latifolia

Oregon Ash.

Lilium pardalinum

Leopard Lily, Panther lily.

Platanus racemosa

California sycamore.

Populus fremontii

Western Cottonwood.

Rosa californica

California wild rose.

Salix lasiolepis

Arroyo Willow.

Vitis californica

California wild grape

Don't treat natives like Broccoli

The non-native plants used in gardens, which are usually easy-to-grow ruderal plants, commonly grow best in amended soil. Without this fluffy soil they will be chlorotic and lifeless. In contrast, where the natives are green and thriving, no amended soil exists. A native plant is not a broccoli plant. Broccoli is a mustard (Brassicaceae). Most of the soils labs give you a soil analysis report based on field crops like broccoli, (even when they say it's for natives). Different plants need different care for optimum growth. Native plants are NOT garden vegetables; native plants as 'different' as you can get. Everything you have been taught all your life on how to grow a wonderful garden is “wrong” when you are talking about how to grow California native plants. Remember that, and most of your gardening will be easier.

Amendments Kill

The addition of any product to the soil that breaks down fast (releases its nutrients quickly to the plant), such as sewage sludge, mushroom compost, 'forest humus', etc. is harmful to most native plants. In cooler sites natives tolerate amending better, the plants die slower. A properly designed native installation should lose one or two plants out of a hundred. The landscape trade in general loses 25-75% according to the difficulty of the site, the condition of the nursery stock and the planting regime. The differences are primarily soil amendments and application of drip irrigation. The physical act of adding soil amendments by turning over the soil and incorporating the soil 'conditioners' breaks up and destroys the fine network of microorganisms that associate with the native plants and without which the native plants are unstable. This is true of all species except the wetland native plant species, having ruderal tendencies, and non-native ruderal plants (weeds). (See also under fertilization.) Do not use any, (any!) nitrified product, no matter how 'organic' it is! Chicken manure will kill our plants in hours, not days.

Polymers cause problems

Do not use polymers as a soil amendment. The plants do not become mycorrhizal, having a symbyotic relationship between plant roots and fungi, because of the constant source of water. Pseudomycorrhiza (parasitic fungal structures) form on roots of native plants grown in this way. The root system is unstable and the plants are difficult to keep alive. Native plants grown with polymers had almost no root growth after 6 months (the soil had that latrine smell). Further, the polymers do not increase the total amount of available water and do not lead to greater water conservation (Letey, et. al.).

Mulch, placed on top of the ground is what native plants prefer; rocks, chipped pine and oak, oak leaves and pine needles and shredded redwood/cedar bark all work fine as mulch (as long as they are used on the right plant). Remember, different plants like different mulch!

Mulch works good with only a few exceptions:

1. Don't use a cheep substitute. Lawn clippings, manure or straw are not good mulch. Free clippings form the local tree trimming service can work, but you don't know what you are getting. If you are in a rural are with native trees this is good. If the mulch is from trees cut in town it will probably not work.

2. Don't spread it thin to make it go farther. It only works if you have at least 3-4 inches. ( Don't over do it either. More than about 6 inches and you will bury your plants.)

3. Fresh Eucalyptus spp., Walnut (Juglans spp.) or Sycamore all have problems. Eucalyptus spp. sometimes is successful in coastal sites, but success is not always repeatable and sometimes results in a partial kill of plants that do not live in association with oaks. Eucalyptus seems to be like an oak tree with an attitude. Use Eucalyptus in certain situations, particularly if you're not in a fire area, after a fire all the seed will germinate into a Eucalyptus forest.

4. Giant bark chunks instead of shreddings on slopes (the bark floats off). It also doesn't hold moisture in very well. The spaces are to large to create a good microenvironment for the good organisms you want. Also, lightweight rock doesn't work where water moves because it moves (float rock, duh).

Remember mother nature wants to cover bare ground, she has a whole batch of weeds waiting in the neighbors fields to cover your site unless you do. (Do not worry about bare ground after a fire in pristine areas, the pioneer plants will take care of it better than man can.)(Curtis; Hanes; Keeley et. al.)

Wildflowers are an alternative but require a lot more work

If you cannot afford wood shreddings, you might consider planting poppies, native vetch (Vicia americana), native lupines, the pioneer wildflowers of your area, or placing rocks next to each plant to cover the ground. It is not as effective as mulch for forest sites but is far superior to bare ground. Moreover, if you plant native wildflowers you're following mother nature's pioneer planting that occurs in the wild. Unlike weeds these species disappear from most yards as the yards mature and you are creating a superior ecology on site without introducing every weed known to man (and woman). BE PREPARED TO WEED, WEED, AND WEED if you do not mulch. When you first start your garden you will not yet have an established plant community. They weeds will come in droves and the wildflowers don't compete very well.

Most mycorrhiza love mulch

Ectomycorrhiza actually keep the mulch and litter from breaking down by capturing the available Phosphorus. VA mycorrhiza are increased by the greater aeration and by the breakdown products created by associated bacteria and other microorganisms. VA mycorrhiza infected roots will not develop secondary offshoots until they encounter this soil-mulch interface. The germination of VAM spores is enhanced by volatile substances produced by actinomycetes working on the mulch. The 'good' bacteria have to be happy also, (as opposed to the 'bad' free living bacteria. The associated (good) bacteria work with and in a fungal system.) Don't worry to much about mycorrhiza, just know its there and try not to kill it!

Use the right mulch for the right ecosystem (plant community and associated fungi and bacteria)

Plant comunity

Appropriate Mulches

Coniferous(pine, fir, spruce, hemlock, etc.) Forest plants

Pine, oak, or redwood mulch

chaparral, scrub, foothill woodland plants

Pine, oak, or redwood mulch mixed with boulders or large rocks

desert, prairie and grassland plants

rocks or boulders with clean bare ground between

(As an aside, in an stable mature ecosystem the understory shade plants are often 'fed' carbohydrates from the overstory trees. (Read, et. al.; Pankow et. al.; Newman ; the Perry series))

In combination with mulch, fast growing pioneers plants should be planted for cover.

Stress tolerant plants are best planted as if they were mature specimens. If they are going to grow to be 10' across, plant them 10' apart. Use fast growing secondary pioneers in between to cover the area until your stress tolerants can mature. This will give you faster fill in and a more weed free, stable planting. Sages, buckwheats, coyote brush and California sage brush, etc. work great for this.

Rock mulch works well for desert plants

In the desert many people have found a 2-3" layer of 3/4" rock solves most weed problems and many watering problems. The rock color makes a little difference. Light colored rock reflects the heat off of the ground up onto the plant. Dark rock will cook the roots unless the mulch is deep. If you need to keep the soil from freezing and night temperatures up, use dark rock. If you want to raise the daytime temperature on the bark or leaves use white rock. This is effective if you have an afternoon wind you can count on, the wind will blow your ground heat away, allowing you to have cooler evenings.

Grassland not weed patch

Grassland species want shallow soils and no mulch, but occasional boulders. PERIOD! No amending, no organic mulch, no small (pebble) rock mulch, no deep soils, no fertilizer, and no mycorrhizal elixir.

Natives do not need fertilizer, daily watering, and soil amending.

Drip is not great. 'Enhanced' sites, all are unstable, and usually the site becomes a weed patch with dead natives in it within 3 years. It seems as barbaric as throwing young women into volcanoes to make your corn grow.

Plant Type

Tolerates drip

Amendments

Fertilizer

Tolerates Regular watering

Ruderal, vegetables, riparian species

yes

needs a lot

yes

yes

Circumventor, grassland, wildflowers, perennials, many shrubs

risky, sometimes works

much more unstable and short lived but looks better off season

seasonally

seasonally first years

Stress Tolerant, oaks, pines, manzanitas

no

no

never

extra ok during 'normal' rainfall pattern of drought year

vegetables

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rushes and sedges

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wildflowers

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most native grasses

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most sages

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most penstemons

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most buckwheats

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most ceanothus

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most manzanitas

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most pines

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most oaks

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