The chemistry behind oxalic acid
As an acid, oxalic acid is corrosive. It is used as an industrial bleaching agent and heavy-duty cleaning product. Apparently, it works especially well on removing rust. Oxalic acid is also classified as nephrotoxin, which means it can damage your kidneys. Oxalic acid, in the form of calcium oxalate, is the most common ingredient of kidney and urinary tract stones. Oxalic acid can also cause joint pain. At high concentrations, oxalic acid really is deadly. According to the National Institutes of Health, lethal doses range from 15 to 30 mg, though an oral dose of 5 mg has been fatal.
In each of these cases, it is the amount of oxalic acid being ingested that is the problem. The levels found in many foods are too low to cause problems. Bottom line, a 150-pound person would need to eat approximately 12 pounds of rhubarb leaves for it to be dangerous. And spinach leaves contain more oxalic acid than rhubarb leaves. That's why your teeth may feel funny after eating spinach. It's oxalic acid crystals binding with any nearby calcium to create calcium oxalate crystals. These crystals stick to your teeth for several minutes to an hour.
Oxalic acid in nature
Oxalic acid is found in a surprising number of food plants that we eat every day. The trick is in the concentration. In fact, oxalates can be toxic to plants, too, but plants bind those oxalates up in crystals that they then use as tiny spears to defend themselves against herbivores. These specialized cells are called idioblasts. Oxalic acid is formed when plants burn sugars and carbohydrates as fuel.
Oxalates are also used to balance calcium levels, within the plant, by binding to calcium molecules. This is why some people say eating high levels of oxalic acid can interfere with healthy bones and teeth, but, again, you would have to eat an awful lot—over a long period of time—to cause any real problems. By the way, our bodies produce oxalic acid out of Vitamin C, on purpose. Also, cooking plants that contain oxalic acid has not been shown to reduce oxalate levels.
Armed with this information, I went out to my rhubarb plant and broke off a young leaf and ate it. The flavor was actually pretty nice, something akin to spinach, but lighter. And I lived to tell about it.
by UC Master Gardener Kate Russell
Photo: South Valley Magazine
This article first appeared in the January 5, 2018 issue of the South Valley Magazine.
All that rain was a little too much for some plants
Many plants have become waterlogged, showing signs of stress through their leaves, which might have twisted and turned yellow or brown. Water stressed plants also might have darkened veins and midribs. The plant often will lose its leaves and new shoots might wither and die.
The symptoms of too much water mirror those of too little water, and there's a reason for that. In both conditions, the plants are robbed of oxygen and nutrients.
Fortunately, the time of year might save many plants. During the winter months most plants are in a dormant or slower state of growth so less damage occurs versus summer floods or monsoons when the plants are actively growing and taking in oxygen and nutrients from the soil.
If you have water-damaged plants, here are some things to do, and not do:
• Stay off wet soil as much as possible. Compaction will only increase the risk of damage.
• Wait until all chance of frost has passed, then trim off damaged branches, shoots and leaves.
• If you are growing in containers, make sure to elevate the pot a few inches off the ground so that water can drain through and away from the roots. If possible, remove the plant from the container and place it on cardboard or newspaper overnight to let it drain. Clean the pot and replant with fresh potting soil and slow-release fertilizer.
• If you are in an area that has flooded, it may be best to discard edible plants that have been submerged in water. According to research from North Carolina State University, flood water may carry pathogens such as E. coli, Salmonella, Hepatitis A and norovirus. The water can spread contaminants throughout the entire garden especially if there is livestock, a pet area or compost pile nearby.
• Produce that is consumed raw, including soft fruit like berries, should definitely be discarded. Plants that were in flower during the flood might be safe, but it's probably best to throw them away as well.
• Root crops that have four or more weeks left before harvest should be OK, but they need to be washed and rinsed thoroughly before eating. Canning produce is not advised.
• Add compost and mulch in late spring or early summer to help reestablish nutrients in the soil.
• If you lose some plants or trees, plant new ones on mounded soil that has been well amended to improved drainage.
• If you are concerned about a tree coming down, consult with a licensed arborist.
• Don't be too quick on the draw with those pruning shears and shovels. Plants are amazingly resilient and may make a full recovery once the rain stops and we get more sunny days.
by UC Master Gardener Rebecca Jepsen
This article first appeared in the March 5 issue of the San Jose Mercury News.
Sheltering fragile plants this winter
In the Bay Area we are also fond of some non-native but wonderful plants. Some are particularly susceptible to frost injuries. So this winter, as you reach for that big soft blanket folded up at the end of our couch, don't forget those beauties in your garden that need a little warming up as well. If you have citrus, bougainvillea, succulents, avocados, or fuchsias in your garden then I'm talking to you. And, unless you're willing to share your blanket (answer: no) then you should have a frost plan. An ounce of prevention for your plants will keep you warm and cozy on the couch. So, take a few minutes to prepare for the next time you find Jack Frost nipping at your rose (couldn't help it…and, side note, roses are very hardy and do not need protection):
- Water the ground around your plants thoroughly to moderate the soil temperature and protect the root zone.
- Wrap (non-LED) holiday lights around the branches of your shrubs and small trees. The small amount of heat they give off is often just enough to ward off the cold. And they're just so darn festive!
- If you haven't yet thrown out your Christmas tree, cut off the branches and pile them up at the base of your plants to keep them cozy. Any other spruce/pine boughs will do.
- Purchase floating row cover from a garden supply store or forage burlap sacks from your local coffee roaster. Wrap and/or drape either of them lightly over your plants. Then enjoy a cup of coffee.
- Bring potted succulents or other tender plants up on the porch where they can bask in the radiant heat of your house.
- Build an elaborate PVC or wood frame around your plants and drape plastic over them. No, on second thought, don't do this. Choose plants that are more suited for your area and you can avoid this all together!
And now, grab that blanket on the couch and sing with me…baby (kale) it's cold outside…
by UC Master Gardener Cayce Hill
This article first appeared in the January 20 issue of the Morgan Hill Times.
By growing different varieties in your garden, you can pick berries year round!
The home gardener loves them, too, and because of our climate and the variety of berries available, we can enjoy pretty much a year-round harvest.
Here are some tips on fulfilling your strawberry dreams:
Berries like full sun and soil that drains well. They also need potassium, so add pot ash when planting in clay soil.
Don't plant where you have grown tomatoes, eggplants or peppers as strawberries are susceptible to verticillium wilt, a fungus that can infect the soil and damage or kill the plant.
Strawberries have shallow roots and need to be watered frequently. Keep plants moist but not soggy.
Strawberries do best when refreshed every year. Dig up and discard of the mother plant. Snip off and replant the healthiest runners that are putting out strong roots and, to ensure large harvests and superior taste, plant new plants every 3 to 4 years.
Varieties
Strawberries fall into three primary categories: Everbearing, day neutral and June bearing.
Everbearing requires long days of sunlight to set fruit and, although they don't bear all year-round, they produce multiple crops in spring, summer and fall.
• Mara Des Bois, developed by a French breeding program, produces small, extremely fragrant, very flavorful fruit.
• Quinault produces up to 2 inch berries that are exceptionally sweet, great fresh or in preserves. It grows well in containers.
• White Carolina, or pineberry, is a unique white to pale pink berry that tastes like a cross between a strawberry and a pineapple. It produces medium size fruit from spring through fall and is heat tolerant and disease resistant.
Day Neutral berries do not depend on a set number of daylight hours in order to flower. They are a great choice if you want a small amount of fruit throughout the year.
• Alpine, sometimes thought of as wild strawberry, is a compact, clumping variety that can be grown in part sun. It has small, aromatic, rich tasting berries. Plants do not sent out runners so it makes a great edging option.
• Albion produces large, firm very sweet berries. It is disease resistant but needs more water and nutrients than other varieties. It spreads out rapidly, so space accordingly.
• Seascape, produced by the University of California in 1992, is productive. Many think it has the best flavor that any of the day neutral varieties.
June bearing strawberries require short day lengths, as in the fall, in order to flower. They are the most widely grown berry and make up the bulk of what you find at the supermarket. They tend to be vigorous plants, putting out lots of long runners, so require room to grow.
They are prolific producers of large fruit, but since the fruit comes on all at once you have to use it all pretty quickly. They are great for jams, jellies and pies.
Unlike the name implies, they don't all produce in June.
• Chandler offers good color and flavor, and the fruit holds well on the vine. It is susceptible to anthracnose disease.
• Earliglow is known for its wonderful strawberry flavor. The fruit is sweet, firm and medium sized. It produces vigorous runners, so give it plenty of space.
by UC Master Gardener Rebecca Jepsen
This article first appeared in the February 1 issue of the San Jose Mercury News.
Winter frost can damage and even kill your plants
Citrus, succulents, newly planted or tender perennials, and many tropical and subtropical plants all are vulnerable.
Frost damage occurs when the water inside the cells of a plant freeze, causing damage to the cellular walls, which degrades the overall health of the plant. Affected plants will wilt and in severe or prolong periods of frost, die.
Shoots, buds and flowers will wither and turn brown or black as if they have been scorched. Even bark can crack or split and die off.
Young, newly planted, specimens are especially vulnerable.
We already have had several days of frost and freeze here in the Bay Area, and it looks like more is on the way. So, how do you protect your prized citrus, succulents, rhododendrons and azaleas?
- If a severe freeze, or multiple days of below freezing weather is expected, water 2 to 3 days ahead of time. This will increase the soil's ability to retain and give off heat.
- Wrapping trunks of young trees with blankets, towels or piping insulation will provide added protection.
- If you are doing container gardening and are able to pull pots into the garage, shed or other enclosed area, that would be ideal. Otherwise, move them up against the side of the house or garage, preferably beneath an overhang.
- Stringing your plants with old-fashioned, incandescent Christmas lights –not LEDs — can be very helpful. Covering the lighted plants with frost cloth, sheets or blankets will add 4 to 8 degrees of protection, enough to keep most plants alive.
- Frost cloth is lightweight enough to leave on for several days, however heavier covers should be removed each day once the temperature has warmed up, and then reapplied each night before sunset.
Make sure the cover goes all the way to ground in order to capture the radiant heat from the soil. Also, stake heavier covers so that the weight won't break branches, damage the leaves or suffocate the plant. You can also use inverted boxes, buckets and plant pots. - Adding a 2- to 3-inch layer of mulch around your plants can also help, but be sure to stay several inches away from the trunk or stem; mulching too close will cause the plant to rot.
- There are many varieties of foliar sprays available today that claim to protect against frost. Although recent field trials have shown no real harm in using them, they also show have found little to no actual protection from these products. You are better off using other methods to keep your plants safe.
- Wait until all chance of frost has passed before trimming off any damaged or diseased branches. Pruning too soon can cause significantly more trauma, even death, to a young, vulnerable plant that might otherwise have recovered in the spring.
by UC Master Gardener Rebecca Jepsen
This article first appeared in the January 8 issue of the San Jose Mercury News.
