- Author: Nadia Zane
A stroll through your garden of late may have revealed some plants with yellowing foliage. There are several possible causes, but iron chlorosis, a condition in which a plant deficient in iron cannot produce sufficient chlorophyll, is common at this time of year. Chlorophyll is responsible for the green in plants and capturing light for photosynthesis, the process in which plants produce food for themselves.
To understand how this could be, it's important to know what's happening in the soil. Iron is one of 17 elements essential for plant growth and metabolism. Iron is typically plentiful in California soils, but certain conditions often make it “unavailable” to plants:
Alkaline soil, meaning soil with a pH of 7.0 or higher, holds on to iron (and many other nutrients), making it inaccessible to plants. Most plants prefer a pH around 6.5.
Soggy and/or cold soil limits microbial activity and the important services they provide in getting nutrients to the plants. Microbes need porous soil and a certain temperature range to thrive, which is why chlorosis is more common in winter. Compacted or heavy soils are especially prone to a lack of porosity in cold, wet weather.
Nutrient imbalances, especially an overabundance of zinc, copper, and manganese, can make iron less available. Causes vary, but can be due to over-application of certain fertilizers.
When determining if you do, in fact, have iron chlorosis, consider factors such as watering, the time of year, and then look at the pattern of yellowing on the leaves. Iron chlorosis presents as green veins with the interspaces being yellow, typically on the newer leaves. Other possible causes include Zinc and Manganese deficiencies or exposure to herbicides containing simazine or diuron. See the UC Integrated Pest Management website for pictures of various patterns of chlorosis:
So what can you do? The key is to focus on improving soil health, which can help lower the pH and increase iron availability. Adding compost to the soil and mulching the surface increases biological activity and improves porosity. If the chlorosis appears only in winter (and isn't severe), then simply wait until the soil dries out, and the problem may correct itself. Be sure not to over-water at other times of the year, not just because it's wasteful, but because it can also induce iron chlorosis.
Selecting plants that tolerate alkaline soil can make things easier. Plants native to arid regions, including California natives and other Mediterranean-climate species, have a better tolerance for alkaline soils than acid-lovers such as Hydrangea, Gardenia, Rhododendrons/Azaleas, Camellias, Hollies, Magnolias, and Blueberries. If you must grow acid-loving plants, be sure to apply plenty of compost and mulch, or try growing them in containers where you can control the soil pH by purchasing acid potting mix.
You may go to a garden center and be told that simply adding sulfur will effectively lower the pH. This is correct if your soil does not contain “free-lime” (calcium carbonate), which cancels out the acidifying effects of sulfur. If you have hard water, then you are more likely to have free-lime in your soil. You can test this by taking a small sample of dry soil and adding household vinegar. If it fizzles, then you have free-lime, and you can return that bag of sulfur along with the iron (I hope you kept receipts for both). Keep in mind that highly alkaline soil (above 7.3 pH) cannot be amended enough to grow acid-long plants without ongoing chlorosis issues.
Applications of iron sulfate or chelates to the soil can correct deficiencies if your soil is sufficiently acidic (6.5 or less) and actually needs iron. Remember that simply dumping extra iron into you soil is not going to fix a deficiency if the soil conditions make it unavailable! Foliar applications are good for a quick-fix, though the effects disappear quickly too, meaning you may need to reapply several times a year.
Be sure to avoid Ironite®, an iron supplement containing toxic levels of arsenic and lead. It has been illegal in Canada since 1997, and is under investigation in California. Aluminum sulfate is another amendment to avoid because of the potential for aluminum toxicity. Gypsum has often been touted as a way to lower pH, but this is not true. It increases porosity (drainage) in clay soils with an imbalance of magnesium and calcium, but if your clay soil is “tight” (i.e. holds on to nutrients; not releasing them to plants) for other reasons, gypsum won't do you much good.
With all these complicated explanations and “don't do this” commands, it's actually all very simple: add organic matter such as compost, only apply as much water as is needed to maintain moderate growth, and use plants that are OK with the soil you have. For more information, see the Colorado Master Gardener Notes on iron chlorosis:
- Author: Nadia Zane
- At a local nursery this past fall, I was excited to find a robust selection of water-wise plants, a reflection of this rapidly expanding market. Another interesting phenomenon, related to me by a nursery employee, was a little less exciting: “customers come in asking for drought-tolerant plants, but change their minds when they see them.” Such news breaks the hearts of Mediterranean garden geeks like me who wish everyone could appreciate the unique beauty of water-wiseplants.
It's understandable to question what the hubbub is all about then water-wise plants are compared side-by-side with traditional landscape species. Negative reactions tend to fall into one of two categories: 1) “they look different from my thirsty plants, and are therefore ugly”, or 2)” if I search long enough, I will find species looking exactly like the thirsty ones I have now.” Although experience will always affect how we see the world, let us attempt to remove our Hydrangea-tinted glasses for a less biased viewpoint by exploring what makes water-wise plants look the way they do.
One of the first things we notice is how sparse water-wise plants look when compared to the lush, full growth of thirstier plants. It's all about water conservation, as smaller and fewer leaves mean less surface area for water to escape from and less to keep cool in the hot sun. While these acclimated plants can appear strange or unappealing at first, contemplating the paradox of growing lush plants with giant foliage in a hot, dry climate, renders those traditional plants a little more bizarre than before.
Another trait shared by many water-wise plants is fuzzy foliage, which is due to hairs on the leaf surface that protect against excess UV radiation. Plants with smooth, bluish-green foliage have a thick, waxy cuticle that also protects against UV radiation, along with reducing water loss. The soft, supple, bright green foliage found on plants native to regions with summer rain is rare among drought-tolerant plants. California plants native to riparian areas where rivers and streams provide roots with year-round access to water are an exception.
Plants native to hot, dry regions tend to be bushy and low-growing; even our native oak trees, which can reach enormous sizes, naturally grow with low-hanging branches when left to their own devices. This adaptation reduces moisture loss by shading the ground, and protects leaves from the wind, which desiccates by whisking moisture away (think about how dry your skin gets on windy days). Although we love our graceful Birch trees, their single-trunk, upright habit almost screams, “take my water away!”
Winter dormancy certainly isn't unique to our climate, but the extreme heat of summer means some plants shed leaves in late summer to reduce water loss. This can be in lieu of, or in addition to, a winter dormancy. Summer shabbiness is difficult to stomach, but there are some drought-tolerant plants that naturally bloom in late summer. California fuchsias and Buckwheats (Eriogonum species) are two prime examples, sending up plenty of beautiful, pollinator-feeding flowers at this difficult time of year, but without requiring excess irrigation.
Visiting a nursery and comparing drought-tolerant plants with the eye-popping pony-packs of Snapdragons and Petunias can be a tad disappointing. Keep in mind that low-water plants are at their best when their roots have room to spread, which can't happen in a little one-gallon container. Starting small and, I admit, a little scraggly at times, they have great potential for maturing into graceful specimens, providing benefits to pollinators and other wildlife, while asking for less water, maintenance, and fertilizer in return.
If you still find yourself unconvinced, a field trip to a water-wise demonstration garden featuring water-wise plants could provide a more realistic view of what these plants will look like as they mature. The SJ County Master Gardeners have a demo garden by the Stockton airport at 2102 E. Earhart Avenue. For more water-wise demo garden locations, or if you have a gardening related question, you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website at sjmastergardeners.ucanr.edu.
- Author: Kathy Ikeda
The word “bee” usually brings to mind an image of a honeybee, but let's also remember the invaluable contributions and amazing diversity of our lesser-known native bee species.
In contrast, California has about 1,600 species of native bees! They are highly varied in size, ranging from 1/10 to 3/4 of an inch long. Many are scarcely recognizable as bees; some are fuzzy and grey, others are metallic green or blue, and some are even polka-dotted.
Some native bees are “social” and form colonies that nest in hives or large cavities. Bumblebees are the only social native bees in California, and they produce minimal honey since their hives last only a year. They are generalist feeders, foraging for nectar and pollen from different types of plants. They are also “buzz pollinators,” vibrating their wing muscles to dislodge pollen from flowers (a process essential to tomato and pepper plants).
The “solitary” native bees are much more plentiful than the social bees, and they generally congregate only to mate. They don't make honey and are much less likely to sting than social bees since they have no colonies to defend. Approximately 70% of solitary bees are ground-nesting, and they must tunnel into bare soil (not soil that is mulched or covered with plastic). The remaining 30% are cavity-nesting, which means they build their nests in tubular holes (hollow stems, burrows bored in wood, etc.). The females build the nests and often sleep in them, while the males shelter outside.
Solitary bees often have very evocative names: mason, leaf-cutting, miner, digger, sweat, cuckoo, carpenter, and more. Many are generalist feeders, but others (such as the sunflower and squash bees) are specialist feeders, which means they depend on a single type of plant as a food source.
Preservation of native bees is vital for both agriculture and a healthy ecosystem. Amazingly, research shows that some native bee species pollinate crops up to two times as effectively as non-native honeybees. Just as importantly, native bees evolved alongside our native wildflowers and other endemic plants and are best suited to be their pollinators.
Sadly, bee populations are declining, sometimes precipitously. While colony collapse disorder is causing sudden die-off in honeybee hives, native bee populations are also increasingly at risk due to habitat loss, pesticide use, invasive plants and insects, and introduced diseases. One unfortunate example is the western bumblebee (Bombus occidentalis), a once common and important pollinator that has now nearly disappeared from California and other states.
We can help protect and sustain native bee populations by:
- Planting a variety of native and ornamental plants with varying bloom times.
- Providing nesting habitat by preserving some open soil and building bee houses.
- Maintaining buffers of high-quality habitat and native vegetation near farmland, and planting hedgerows with diverse plant species.
- Reducing or eliminating the use of broad spectrum and systemic insecticides, which can harm all types of bees.
To learn more, read “California Bees & Blooms,” an excellent book written by several University of California bee experts. For bee identification guides, pollinator plant lists, and other resources, visit the Xerces Society website (www.xerces.org/pollinators-california-region/). The UC Berkeley Urban Bee Lab website (www.helpabee.org/) has an excellent overview of our state's native bees, information on bee gardening, and instructions for building bee boxes. To see a wide variety of bees, visit the Häagen-Dazs Honey Bee Haven, a public garden near the U.C. Davis campus.
For gardening related questions, call the UC Master Gardener office at 209-953-6112, or use our website: http://sjmastergardeners.ucanr.edu/CONTACT_US/.
- Author: Nadia Zane
This time of year finds us cleaning up the garden and throwing away the trimmings without ceremony or thought. This
Defining waste is tricky, but you could think of it the same way as weeds, which are basically plants where you don't want them; like weed management, reducing garden waste comes down to re-thinking and altering your cultural practices:
Plan ahead: Shopping at a nursery without a plan is like going to the grocery store hungry; impulse buys are inevitable! Measure your space, research climate-appropriate plants, and call nurseries for availability. Try to favor evergreen (non-deciduous) species, limit herbaceous perennials and annuals, and provide all plants adequate space for their natural size and shape. Constant shearing is a waste of time, and planting too densely often means you are tearing out plants within a couple of years, a waste of the water and other resources that went into growing those plants.
Irrigate and fertilize appropriately to avoid the feedback loop of wasteful inputs: too much water and high N-P-K fertilizers create lush growth, which is more attractive to pests, requiring herbicides and more irrigation to keep up with all that growth. Potent fertilizers often leach below the root zone or out of the soil via irrigation run-off, polluting rivers and groundwater, and wasting your money. Organic fertilizers with low N-P-K numbers provide a slow release of nutrients, which can be taken up more effectively by soil microbes and plants.
Composting is the best way to recycle myriad forms of plant matter, both from your yard and the kitchen, into a source of bio-available nutrients. Compost also helps improve soil structure (a definite plus for those of plagued with adobe) and increases the biodiversity of your soil, a way of protecting your plants from pathogens.
Grasscycling: Recycling grass clippings by leaving them on the lawn reduces fertilizer needs by 20% and returns valuable organic matter to the soil. It's easier on your back, too! Problems associated with grasscycling often result from improper practices; see the resource section below for help.
Avoid invasive species: Some plants have aggressive growth and produce a lot of waste when they need trimming. Examples of invasive species include English ivy and Vinca major. Some invasives can re-root in a compost bin, so they end up in the landfill. for examples of invasive plants and alternatives, see the California Invasive Plant Council (Cal IPC) website.
- Author: Nadia Zane
Like most succulents, Dudleyas have fleshy, swollen foliage that stores water. Another key trait is their farinose coating, which is made up of loose wax particles that come off when rubbed, giving many Dudleya species a blue-gray tinge. Do not try to remove this coating, as it provides UV protection. When seen on fruits such as blueberries or plums, this wax is known as a “bloom.”
Dudleyas come in two forms: branching and unbranching. Branching dudleyas tend to form spreading colonies and are best used as ground covers in the garden. Unbranching types form large rosettes and are great as focal points. Both kinds like containers and have a long life span, living 50-100 years, given the right conditions. They are perfect for rock retaining wall crevices, as this is how they naturally grow.
The species listed below are frost tolerant but need afternoon shade in the San Joaquin Valley heat:
Coast dudleya(Dudleya caespitosa): 4”-6” high, spreading (not invasive)
Liveforever (Dudleya cymosa): 6”, spreading (not invasive); hardiest to heat and cold of the species listed here
Cliff lettuce (Dudleya farinosa): 12” rosette
Chalk liveforever (Dudleya pulverulenta): 12” – 24” rosette with a thick, farinose coating.
Although most succulents require little irrigation, many come from desert climates where there is a winter and summer “wet” season. Unlike the desert succulents you typically find in nurseries, native Dudleyas evolved in our summer-dry Mediterranean climate, and often lack resistance to pathogens associated with summer moisture. This is is why Dudleyas are best combined with other plants that also dislike summer irrigation, such as Coyote mint (Monardella villosa), St. Catherine's lace (Eriogonum giganteum), Purple needlegrass (Stipa pulchra), or Chaparral currant (Ribes malvaceum).
Dudleyas are easy to care for, given the right conditions. Flower stalks can be removed when bloom is over. Either wait until they are dry enough to pull away easily or cut with pruning shears to avoid accidentally uprooting the entire plant. Resist removing all of the old, dry leaves, as these help stabilize larger single-rosette types (a long, exposed stem is easy to knock over).
Soggy soil can be a problem for Dudleyas, so provide good drainage and plant so that they are tilted sideways, allowing water to run off. If planted in clay soil, avoid watering in the summer; in sandy soils, some summer water is OK. They will naturally die back at the end of summer without irrigation, often turing red as the foliage desiccates, before regenerating when fall and winter rains begin. Avoid trying to circumvent this natural cycle with extra irrigation, as it may shorten their life span by increasing their susceptibility to root rots. You can also prevent root rots and fungus problems by mulching with gravel and avoiding organic materials such as bark.