Enriching the Soil with Cover Crops

Every drop of rain that hits bare soil is destructive. Over 3000 years ago the Chinese protected their soil from erosion and increased fertility by planting cover crops. Early Nile Valley inhabitants 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. Planting a cover crop is another way to improve and retain your soil. One of these days winter rains will come so be ready.

A cover crop is really anything that covers the soil and protects it from rain, trapping nutrients and preventing them from leaching downward. 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.

Orin Martin of UCSC’s Alan Chadwick Garden shows the extensive root system of bell beans.

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. Growing a cover crop also increases beneficial soil bacteria.

Fava beans, when grown as a cover crop and tilled into the soil in spring, increases soil fertility.

Cover crops are called green manure when they are chopped up and turned into the soil in spring before 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.

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.

Recent research now recommends planting a mixture 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 nowhere near as efficiently as bell beans. Crimson clover seed is 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.

You don’t need to use an inoculant on legume seed. 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.

Work the soil lightly with a metal bow rake then broadcast 8-10 seeds per square foot. Weeds should be already cleared but this step doesn’t have to be perfect. Afterward the area should be raked again lightly 1-2 inches down and covered with 3-4 inches 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. Water in lightly.

If you plan to let your small vegetable garden lie fallow over the winter instead of planting it with a cover crop you can cover it with manure and straw and I’ll talk about that in another column.

Fall Color & Climate Change

Although it’s a bit early around here to see fall colors it’s happening at the higher elevation. Or is it? Have the wildfires affected the changing of the leaves? And what about the effects of ongoing climate change? How is our planet changing?

Ebbet’s Pass

Quaking aspen (Populua tremuloides) is the most widespread tree species in North America. They generally grow in high altitude areas but also exist at sea level in places like the state of Washington along the Pacific coast where climate conditions are ideal. Quaking aspen provide food for foraging animals and habitat for wildlife. They also act as a fuel break retaining much more water in the environment than do most conifer species.

High mountain systems, such as the Sierra Nevada, are uniquely sensitive to global climate changes and act as “canaries in the coal mine” providing early signals of significant climate-driven changes. Research in the Sierra Nevada by Pacific Southwest Research Station, a USDA Forest Service research organization, shows how vegetation has responded to climate in the past and indicates changes that might be coming in the future over the next decade.

Climate has a profound influence in shaping our environment and natural resources. By looking at tree ring records of living and ancient wood and pollen lake sediments present, climate can be compared to historic patterns to show climate changes.

Research indicates a complex, unpredictable future for aspen in the West, where increased drought, ozone and insect outbreaks will compete with carbon dioxide fertilization and warmer soils with unknown cumulative effects. Aspen are vulnerable in the face of climate change. Hopefully, we will not lose this wonderful tree in California.

Weather conditions play a major part in the intensity of fall color. The time of year is nearly consistent but some years the show is more dramatic than others. The best conditions for intense leaf color to develop are dry sunny days followed by cool, but not freezing nights.

Recent wildfires have had an effect on changing leaf color. Not much had been studied in this field prior to the 2018 fires that ravaged our state. Researchers’ measurements have shown that the total amount of sunlight available to a plant for photosynthesis decreased only slightly – about 4% – compared to the previous summer. The smoke didn’t block the light but scattered it. Direct sunlight might fall mainly on the upper foliage but diffuse light can reach greater number of leaves throughout the canopy. So smoke can have some affect on photosynthesis but not much more than a cloudy day. Oxidative stress levels can occur during expended smoke exposure, however, so for the health of your plants be sure to wash the leaves off after a smoky day.

Which plants put on the best show in our area? Here are some of my favorites.

California native Western redbud turns yellow or red in the fall if conditions allow. This plant is truly a four-season plant starting in spring with magenta flowers, then leafing out with apple green heart shaped leaves. Colorful seed pods give way to fall color. This small native tree or large shrub does well as a patio tree in gardens with good drainage.

Other native plants like spicebush and Western azalea turn yellow or gold in the fall. A native vine that lights up with the onset of autumn is Rogers Red California grape. If you have an arbor, wall or fence that needs covering quickly this is your plant. The green and gray leaves are transformed in autumn into great draperies of rich, scarlet leaves with clusters of summer fruit turning all shades of purple.

Edibles that turn color in the fall include blueberries, pomegranate and persimmons.

Trees and shrubs that do well in our area and provide fall color include Chinese flame tree, ginkgo, Idaho locust, Chinese pistache, crape myrtle, witch hazel, all maples, liquidambar, katsura, dogwood, locust, cherry, crabapple, oakleaf hydrangea, barberry and smoke tree.

More on our own fall color later.

Plant Bulbs Now

This fall I’m at a new garden in Ben Lomond. I’ve brought down every potted plant from my property in Bonny Doon that was showing signs of regrowth after the fire. I figured if they were trying to survive after 6 weeks with no water, some in melted plastic pots and tops burned off who was I to deny them a chance to live? I had 250 potted plants. Yes, I know, what was I thinking? Anyway, with lots of empty glazed empty pots here I’m looking forward to planting bulbs this fall.

Daffodils and narcissus are are toxic.

There are a lot of squirrels here in this garden. I’ll have to outsmart them. Squirrels, mice and moles are observant and crafty. Once they discover newly planted bulbs, they’ll assume it’s food. Just disturbing the earth is a tip off for them. Daffodils and narcissus bulbs are toxic but if they dig them up then leave them exposed with just a nibble taken, so much for any spring flower display. Protect your bulbs with wire baskets or spray them with foul tasting repellent, letting the spray dry before planting. You can also bury the bulbs with ground up egg shells. Another way to foil squirrels is to plant the bulbs deeply, This only works if you have good drainage, however. Next year, if the squirrels start nibbling the foliage as it emerges try spraying it with hot pepper spray.

Forest Lily – long lived bulbs that bloom for a very long time.

One of the more unusual bulbs I grow in pots is Forest Lily (valthemia bracteata). I got several bulbs over 25 years ago and fortunately divided them last year to give as gifts. If the burned ones I now have don’t come back I can ask one of my friends to divide theirs and give me a few. The bulbs are enormous and bloom for months. The handsome foliage lis thick and wavy, looking somewhat like a succulent but it’s the huge, showy dark pink flower spikes that bloom from February to May that I love. Grow them light shade and allow them to go summer dormant. Valthemia are native to the northern Cape area in South Africa where it grows on rocky slopes along the famous Namaqualand Flower Route.

I love those huge, showy tulips as well as the new colors of daffodil and narcissus coming out each year. I’ve wanted to plant Spring Starflower or Ipheion for a long time. Their starry white flowers bloom over a long period in spring and they naturalize easily. Spring Snowflake ( leucojum vernum ) will also naturalize in the garden. The flowers are small and bell shaped, white with a green or yellow spot and have a slight fragrance. And I want to include some species tulips. They will re-bloom year after year just like they do in the wild in Europe, North Africa and Asia.

Another bulb I’ve wanted to grow for a long time is Ixia viridiflora. They need to be completely dry in summer so planting in pots will be perfect for this most striking and unusual bulb. Few plants can beat it for sheer brilliance of flower. Each flower is a brilliant turquoise green with a purple-black eye in the middle. The dark eye is caused by the deep blue sap of the cells of the upper epidermis. The green color is due to the effects of light being refracted from the cell wall and granules embedded in the pale blue cell sap. Amazing flower.

Tulips can be grown in sun or light shade.

What about bulbs in the shade? Bulbs that will bloom in light shade are crocus, scilla, tulips, grape hyacinth, leucojum, snowdrops, chionodoxa and lily of the valley. Many from the daffodil clan, including jonquils and narcissus will grow, bloom and naturalize year after year under tree canopies or other lightly shaded areas.

Whatever you bulbs you choose to try this fall, you will be happy you planted some bulbs come spring. And to help them bloom again the following year fertilize them at the time of planting with bulb food or bone meal worked into the soil a couple inches at the bottom of the hole. Mature bulbs respond to an early spring feeding with the same fertilizer.

Sweet Peas in the Garden

There is so much clean up to do around the garden in the fall but I think we should all do something fun. A couple years ago I got an email about when to plant sweet peas. This reader had collected seeds from the wild pea, lathyrus latifolia, and wanted to know when to plant them. Although the flowers of this perennial sweet pea are not fragrant, the culture is the same as all sweet peas. Now’s the time to plant.

Everlasting sweet peas are super easy to grow.

The perennial or everlasting sweet pea we see growing wild is not native to our area. It has naturalized throughout the United States and Canada after having been introduced from the Mediterranean area in the 1700’s. It can be invasive but if it’s growing in an out of-the-way spot where you can enjoy the bright pink blossoms they require little care.

Who doesn’t love old-fashioned sweet peas? A small bouquet will perfume an entire room with a delicious scent. They remind me of my Aunt Ruth who grew them every year and let me pick a bunch each spring whenever I went to visit. There are many new varieties and colors these days but back then her sweet pea vines were covered with the classic mixed colors of violet, blue, pink, peach and white.

Mixed bouquet of spring flowers including sweet peas.

Sweet peas have been around for a long time and many different countries claim that they originated there. One story is that a monk, Father Cupani, first harvested them in the wild on an island off Sicily in 1695 and sent the seeds to the Netherlands. In the 1800’s, a Scottish nurseryman named Harry Eckford began hybridizing and introducing larger varieties in a wider range of colors and they became quite a sensation. The most famous and perhaps the most important use of this flower was the extensive genetics studies performed by Gregor Mendel. Since peas self-pollinate, their characteristics such as height, color and petal form could easily be tracked. But whether they came from Ceylon, the modern day Sri Lanka, China or Sicily, heirloom sweet peas are as exquisite in the garden as they are in the vase.

Pant early blooming types of sweet peas in October or November. These varieties flower in the shorter days of late winter. Winter Elegance and Early Multiflora are common early flowering types. Also plant some of the fragrant spring flowering heirlooms and Spencer’s at the same time to extend your harvest time.

Highly fragrant Black Knight sweet peas make good cut flowers.

My very favorite sweet pea with long stems for cutting and an intense fragrance of orange blossoms and honey is called April in Paris. Large ruffled blossoms are a soft primrose cream, tinted at the edges in dark lilac that deepens and increases with age. But maybe it’s Black Knight that’s my favorite sweet pea with those dark maroon strongly scented blossoms. You can’t go wrong no matter what color or style sweet pea you choose. They attract bees, butterflies and hummingbirds. Deer generally ignore sweet peas. Sweet peas are not edible and may cause stomach upset.

Enjoy Fall in the Garden

Bearded iris can be divided when they become crowded and unproductive

Fall is a favorite season for many people. The heat of summer is just about over and our gardens can breathe a sigh of relief. Well, actually I’ve never heard any plants sigh but I know they can communicate with one another. For us up here in the Santa Cruz mountains, this is one of the best times to be outside. Here are tips for early fall in the garden.

Late fall is not a good time for major pruning so if you have some shrubs that need a tune-up do it soon. Wounds heal slowly later in the fall, leaving them more susceptible to disease. As a general rule, don’t prune when leaves are falling or forming. Wait to prune most trees until late in the dormant season or in late spring after leaves and needles form. To avoid sap flow on birches and maples, prune after leaves mature. Fruit tree summer pruning should have already been done when growth ceased.

Refresh perennials, such as butterfly bush, salvia and yarrow by cutting a third to half of their growth later in the fall.

Rake leaves- compost or put in your green can. If large leaves are left in place they will mat down and set up fungal problems come spring.

Remove dead and diseased leaves from under camellias, rhododendrons and roses.

Divide perennials like alstroemeria in the fall

Now through October, divide summer blooming perennials that are overgrown and not flowering well. Alstroemeria, agapanthus, coreopsis, iris, daylily, yarrow, rudbeckia, calla lily, aster and penstemon fall into this category. You can also divide spring blooming perennials like candytuft, columbine, astilbe, bergenia and bleeding heart although they don’t always bloom the first spring afterwards due to the energy they use re-establishing themselves. If you’re on a roll out in the garden, though, go for it now. You never know what other projects you may be working on next spring.

Start perennial flowers seeds now so that they will be mature enough to bloom next year.

Fertilize shrubs lightly one last time with an all-purpose organic fertilizer or layer of compost. Use compost only on California natives.

Plant cool season veggie starts like broccoli, cabbage, cauliflower, chard, lettuce, spinach, brussell sprouts, onions and leeks in soil enriched with 4-6 inches of compost as summer vegetable crops will have used up much of your soil’s nutrients.You can sow seeds of beets, carrots, radishes, spinach, arugula, mustard and peas directly in the ground. Planting early ensures your plants get a good start before cold weather sets in and growth mostly stops until spring. You’ll be able to start harvesting in just a couple months if you start now that the weather has started to cool.

If you aren’t going to grow vegetables in the garden this fall consider planting a cover crop like bell beans, fava beans and vetch after you’ve harvested your summer vegetables. Next month I’ll talk about how to go about doing this and how this benefits your soil.

Cut back berry vines that have produced fruit. Canes of the current season should be trained in their place.

Spider mites and thrips are especially prolific during early fall. If some of the leaves on your plants are pale with stippling, spray the undersides of infected leaves with organics like insecticidal soap switching off with neem oil as they build up a resistance to one of the pesticides. Plan to spray with a horticultural oil in the winter to kill overwintering eggs.