Category Archives: organic weed contol

Growing Cover Crops – Part II

Orin_Martin_bell_beansOrin Martin of the Alan Chadwick Garden on the UCSC campus is widely admired for his incredible knowledge and skills as a master orchardist, horticulturalist and teacher. I was lucky a couple of years ago when he visited a group of fellow designers and brought his favorite russet apples. Another time he brought a dozen different kinds of potatoes that we roasted, critiqued and thoroughly enjoyed.

The Alan Chadwick Garden was nothing but poison oak and chaparral in 1967 when Alan Chadwick first got his hands on it. Martin came to UCSC in 1969 as a literature major but was soon impressed with Chadwick’s work, preaching the gospel of treating the garden as a self-nourishing system. Together they worked the garden, building the soil and teaching others.

Now Martin runs the appreaster_Michaelmas_daisy.2048ntice program which teaches future organic gardeners and shares his knowledge in workshops like the Cover Crop class I recently attended.

Last week I wrote about how and why to plant cover crops. This is what to do next spring after they’ve done their magic in the soil fixing nitrogen.

Cover crops are plowed or skimmed off in late February to early April. Because it takes 3-5 weeks for the cover crop to break down so crops can be seeded or transplanted, it is often best to skim off the cover crop at the base of the plants and combine with straw or leaves to make compost. Previously made compost can then be applied to the surface. It is important to retain the roots and nitrogen-filled nodules in the soil. Take only the vegetative portion.

cover_crops_Orin_Martin.1280Another method is to skim the foliage with a weed wacker or mower chopping it into small pieces 1/4″ to  4″ long. You can then rototill this into the soil and allow it to decompose on its own. In about 2 weeks the material should be broken down to be unrecognizable as plant material before replanting.

If you are developing your soil to build organic matter and improve structure incorporate the cover crop at a more mature stage (half to full bloom) when it has a higher carbon content. The nutrients will be stored in the reservoir of humus and released slowly over a number of years.

On established soils where you want primarily to fertilize next spring and summers crops, incorporate the cover crop after skimming and chopping when it has just started to flower as it decomposes quickly at this stage.

The Chadwick Garden fertilizes its established fruit trees by simply cutting down the cover crop growing at their base with a machete at the 25% flowering stage. 4-6″ of wood chips are laid over the chopped up pieces and left for nature to decompose. That’s all their is to it. Martin explained that the garden used blood meal and the organic fertilizer, Sustane, during the first several years while the trees were becoming established.

Picking up a clump of grass sown just 2 weeks ago, Martin teased off the soil to show the vigorous, fibrous root mass. “This is why the riches soils of the world, the Steppes of Russia and the original Midwest prairies, are so fertile and are called bread basket soils”, he explained.

Plant a cover crop this fall and your soil will be richer for it.

Growing Cover Crops- Part I

Every drop of rain that hits bare soil is destructive. Over 3000 years ago the Chinese knew how to protect their soil from erosion and increase fertility by planting cover crops. Early Nile Valley inhabitants 3500 years ago also practiced this method of agriculture as did first century Romans. Lupines were planted in poor soil when no animal manure was to be had. I learned this and also how to protect and improve my soil from Orin Martin, manager of the Alan Chadwick Garden at a cover crop workshop recently on the campus.

aster_Michaelmas_daisy.2048“It’s all about the biology of the soil”, Martin said. “You grow the soil that helps you grow the plants”. A cover crop is really anything that covers the soil and protects it from rain, trapping nutrients and preventing them from leaching downward, he explained. Cover crops can increase the tilth of the soil. Quick germinating grasses easily loosen the top foot of soil with their root mass. Legumes have a tap root, a bio drill, that penetrates 30″ downward while alfalfa roots can grow even deeper.

Cover crops like bell beans, vetch and fava beans are especially valuable as they increase nitrogen levels in the soil in two ways. Atmospheric nitrogen can be “fixed” and left in the soil to fertilize subsequent crops. This is in addition to the nitrogen left from the foliage of the legume.

Cover crops are also called green manure when they are chopped up and turned into the soil in spring lettuces_after_cover_cropping.1024before going to seed. The planting of legumes like peas and beans can actually increase nutrients in your soil giving you a net gain which is needed to offset what you take out of the soil when you harvest fruits, vegetables and flowers.

From late September to the end of November is the best time to sow cover crops. You will need to irrigate lightly a couple times per week if it doesn’t rain. You can also wait to sow just before the rains start. Be careful about working overly wet soil however as you can ruin the structure of your soil.

The Chadwick Garden, Martin explained, originally was heavy red clay. 35 years of soil building with bell beans and vetch cover crops and compost have established a level of fertility that now supports several acres of vegetables, fruit trees, berries and beneficial flowering plants. Fall-sown, spring ploughed-down cover crops are the sole fertilizer used for the better part of the last decade.

Soil_builder_cover_crop_mix.1600Martin explained that recent research now recommends planting a tandem of grasses and legumes. Annual cereal grasses such as oats, rye and barley germinated quickly to hold and shield the soil until the legumes take hold. Bell beans, fava beans and vetch which are the best legumes for our area grow slowly the first 3 months then take off growing 70-80% in the last 3 months. The ratio of grass seed to legumes can vary from 10% to 30%.

There are other legumes that fix nitrogen but no where near as efficiently as bell beans.  Crimson clover seed is also more expensive, needs lots of water to sprout and competes poorly with weeds. Mustard causes competition with the fruit trees as bees will concentrate on the mustard flowers instead of the fruit tree flowers.

A question came up about using inoculants on legume seed. Martin explained that our soils have a native resident population of good bacteria that will break down the seed coat and encourage the plant roots to fix more nitrogen especially after cover cropping for a few years.

We all followed Martin out to the cover crop trial plots to see how the different types were growing. Bark chips will soon be applied to the paths. All of the gardens are mulched several times per year with wood chips. A 10 year study, Martin explained, demonstrated the amazing benefits of ramial chipped wood which is the type the tree service companies provide for free.

We watched him work the soil lightly with a metal bow rake then broadcast 8-10 seeds per square foot. Weeds were already cleared but Martin said this step doesn’t have to be perfect. Afterward the area was raked again lightly 1-2″ down and covered with 3-4″ of straw. Wood chips would be fine, too. Mulch heavier if you have bird competition. Cover crops are vigorous and will come up through just about anything, he said.  Water in lightly.

There are 3 ways to fertilize, Martin said. You can buy chemical fertilizer which is expensive and doesn’t do much for the soil. You can apply compost, which being carbon based, ramps up beneficial fungal organisms in the soil. Or you can cover crop or grow green manure which increases beneficial soil bacteria. Orin Martin has proof of the benefits of the last two methods.

What to Do about Invasive Plants

bull_thistleWe can't control those pesky weed seeds that blow into our gardens and take hold. There are ways to keep them from taking over, however. But what about those invasive plants that are already in our gardens like ivy and vinca major? What's the best way to deal with them? Then there are plants we buy ourselves that can invade natural areas. Are there better plants to use that are just as attractive and useful? Here are some solutions to make your garden happy.

One invasive thug that can take over is bull thistle, a relative of the edible artichoke. The seeds of this vigorous exotic take hold in disturbed areas including your beautiful garden soil and if not controlled can become a solid mass of impenetrable thistles in just a few seasons. Bull thistle only reproduces by seed so removal of the flowering stalks at this time of year will prevent them from spreading. The flowering heads must be discarded in a plastic bag and destroyed to keep them from forming viable seed. Because this weed is biennial you also need to dig out the first year plants that have not formed stalks. You can also mow thistles close to the ground a couple of times before they form stalks to reduce the population over time.

As a landscape designer and consultant I'm often called upon for advice for an area covered with vinca major or ivy. Both of these invasive species are too successful for their own good, smothering native plants and harboring pests such as rats and snails. Vinca major also serves as a host to the bacteria that causes Pierce's disease in grapevines. For your information, vinca minor has not been found to be invasive in California so far

You can choose organic methods to control vinca and ivy rather than chemical herbicides. Hand vinca_majorremoval is labor intensive but the results are good if all the root nodes and stolons are removed. Work inward from the perimeter of the patch and pull the plants back. You will need to do this every 3 months during the first year to remove resprouts but native plants may recolonize the area and reduce the chance that other weeds will move into the area following the disturbance caused by the removal activities.

Replanting with another more desirable groundcover is another solution. For shady areas, try planting wild ginger  (Asarum caudatum), Catalina perfume ( Ribes viburnifolium), creeping snowberry ( Symphoricarpos mollis), yerba buena ( Satureja douglasii ), bear's foot hellebore (Helleborus foetidus), winter saxifrage (Bergenia cordifolia), pachysandra, Serbian bellflower (Campanula poscharskyana) or Asian jasmine.

Good substitutes for vinca or ivy in sunnier spots include groundcover types of manzanita and ceanothus. Also attractive are Taiwan raspberry (Rubus pentalobus), California fuchsia (Zauschneria), or beach strawberry (Fragraria chiloensis ).

Some plants even though purchased from a nursery can cause problems. You wouldn't buy a Scotch or French broom knowing how invasive they can be. Forsythia, Japanese kerria, golden currant and Jerusalem sage all provide that beautiful spring butter yellow color in the garden.

The licorice plant (Helichrysum petiolare) gained popularity for its deer resistance and foliage color many years ago. Unfortunately, it self sows wildly and the spreading branches will root at any point of contact with the ground. Try instead better behaved plants like California natives salvia leucophylla or eriogonum giganteum. Teucrium germander or Powis Castle artemisia also work well in the same area.

Another good plant gone wrong is cotonester  lacteus (parneyi).  The red fall berries are spread by cotoneaster_lacteus_Parneyibirds and with their rapid growth and competitive roots they can overtake the garden and wild areas. Fortunately there are many other plants to use instead that provide food for birds and are beautiful, too. Try planting toyon (Heteromeles arbutifolia) a California native with delicate white flowers and large clusters of brilliant red berries. Pineapple guava is another good substitute as is strawberry tree (Arbutus unedo).

These are just some of the suggested alternatives for invasive garden plants for this area. Don't give an invasive an inch, it can take over your garden, the neighbors and our wildlands.
 

Watering, Fertilizing and Weed Control

Whether you grow a full-blown vegetable garden or a few herbs and edible flowers in containers, celebrate this Fourth of July by serving a menu created with produce harvested from your own garden. It may be too early for your corn or tomatoes to be ready but peas served with a touch of basil would be delicious. A fellow gardener recently told me that she loves steamed baby zucchini cooked with a small pinch of lavender flowers. I haven’t tried this myself but it sounds interesting, maybe garnished some some edible nasturtium or viola flowers.

Actively growing vegetables and flowers need a boost from They use a lot of nutrients, especially nitrogen, at this time of year. Add water soluble fertilizer to your drip irrigation system or apply it through a hose-end sprayer. Sprinkle dry fertilizers over the soil around the plants or apply in trenches next to the rows. Water deeply afterward.

Remember that weeds compete with vegetables and flowers for moisture, nutrients and sunlight. Weeds can also serve as alternate hosts for disease and pest problems. You can prevent weeds from getting out of control by using the "half-hour" rule. Weeding for just half an hour every couple of days will save you hours of hard work in the future. By staying ahead of the weeds, you’ll grow more healthy produce and flowers.

If you battle dandelions and don’t want to use chemical weed killers around pets and children, get out the white vinegar from the cupboard. On a hot sunny day spray straight white vinegar directly on the weed. This method will kill whatever it touches so direct the spray carefully. If the dandelion is in the lawn, wait a week, pour some water on the dead spot to dilute any lasting effects of the vinegar. then pole a bunch a holes and drop in some grass seed. Sprinkle a bit of fertilizer where the seed is planted and keep the area moist. In three weeks you won’t remember where the dead spot was and the dandelion will be long gone.

Trees are the most important living asset on your property. They cool your house and offer shade and protection for your plants. They provide food and shelter for birds and other wildlife. Summer heat can take a toll on trees. Fruit trees, citrus and flowering trees need a deep irrigation every other week. Less thirsty established trees like Chinese pistache and strawberry tree need irrigation about once a month. Newly planted trees need water regularly. Gradually reduce frequency after a year or so.

There are ways to maximize the efficiency of the water you apply.  Drill several 4" wide holes about 24-30" deep around the drip line of the tree, being careful not to damage large roots. Fill the holes with compost and water.   Or you can use a soaker hose on the surface to slowly water the tree.   Mulch heavily all planting beds. Do not use rocks or gravel as a mulch because hey add heat to the soil and moisture evaporates faster.

Happy Fourth of July.