Mulch under Citrus Trees: Pros and Cons

I love mulch. That would be obvious to anyone who has ever talked gardening with me. Big piles, small piles, inches of mulch scattered everywhere. Love it!

The benefits of adding organic mulch (wood chips, shredded tree limbs, pine needles, compost, straw) to the top of your garden soil:

• retains moisture

• keeps soil temperature constant, reducing plant stress

• suppresses weeds

• gradually increases soil organic matter

• attracts beneficial organisms that improve soil fertility and porosity.

• Mulch encourages healthier plants, reducing the needs for pesticides and fertilizers.

• protects roots and plants from mechanical injury.

• On hillsides and around homes, it suppresses the spread of brush fires.

But a long-held recommendation from the University of California flies in the face of the "all mulch, all the time" rule regarding protecting citrus from the effects of freezing temperatures: "A cover crop or mulch can lower minimum temperature at night, posing an increased threat from freeze damage." 

So, our advice has been over the years, "rake away mulch from beneath citrus before an expected frost or freeze".

Now, the California Landscape Contractors Association is offering the opposite advice in a release regarding frost protection: "Mulching with a partially composted material is one the best ways to protect plant roots because it helps insulate the soil, reducing heat loss and minimizing temperature fluctuations. Protecting the roots is necessary in order for them to survive the cold."

So, who's right? Sacramento County Farm Advisor Chuck Ingels says: keep on mulching!

"The CLCA is right on," says Ingels. "In our mild climate, mulch doesn’t protect the tree from cold because the soil and roots really don’t ever freeze. Mulch protects the soil for other well known reasons. Regarding that UC study: years ago I thoroughly researched this and wrote about it in "Protecting Groundwater Quality in Citrus Production". In a large orchard, the best orchard floor conditions for reducing frost hazards is bare, firm and moist soil. The sun hits the soil and re-radiates the heat at night, warming the air. Tall cover crops are worst because not only do those plants not hold much heat, but tall cover crops raise the level of cold air (cold air sinks), increasing frost damage potential."

"Perhaps with just a few citrus trees there may be some benefit in this regard," Ingels concedes. "But any difference is generally very miniscule. What happens on the surrounding five acres (asphalt vs. buildings vs. bare ground) affects the air temperature around your tree. So, mulch away!"

ROOT ROTS + MOISTURE + MULCH = TROUBLE FOR CITRUS TREES
But wait a minute, here's another reason why mulch and citrus trees may not be the best of friends: phytophthora. The spread of this root and crown rot fungal disease may actually be aided by too much mulch beneath shallow rooted citrus trees, especially in moist, slow-draining soils. According to the UC Division of Agriculture and Natural Resources book, "Pests of Landscape Trees and Shrubs", "phytophthora kills the roots and root crown area of infected plants...possibly causing mature plants such as citrus to grow slowly and gradually decline... Phytophthora may affect only small feeder roots or rootlets, major roots or all roots and the crown... Because mulch retards drying of the soil and excess soil moisture greatly contributes to the development of root rots, improper or excessive use of mulch may actually promote root rot development."


TO MULCH OR NOT MULCH CITRUS? A COMPROMISE.

 If your soil drains easily and is not compacted, you may be able to get away with adding a few inches of mulch beneath your entire mature citrus trees, but keep the mulch from touching the trunk; six inches away, at a minimum. But if you have clay soil, slow draining or compacted soil, or just want to play it safe, Debbie Flower, Professor of Horticulture at American River College in Sacramento, offers this advice to stave off decline in a citrus tree: place the mulch from about two feet away from the trunk to beyond the outer canopy of the tree. 

 


For newly planted citrus, move the mulch to the outer edge of the canopy (and beyond). 












This way, the shallow roots near the root crown (as well as the crown area itself) have less of a chance of getting root rot problems. Another strategy: plant citrus in raised beds to improve drainage.

Poinsettia Pointers

Sure signs that December is upon us: Bob Dylan's "Christmas Island" is heard between announcements for deli tray bargains in the supermarket; Christmas tree lots pop up, seemingly overnight, on bare street corners; and everywhere you shop, rows and rows of that brilliant red holiday plant, the poinsettia, fill the front area of the stores.

Among the varieties available are poinsettias that expand your color choices, beyond basic red. New colors include peach, salmon, coral, white, rose, pink and variegated combinations of those shades. 

Here's what to look for when hunting for a healthy poinsettia:

• Avoid purchasing poinsettias from outdoor displays. Temperatures below 50 degrees can rapidly shorten a poinsettia's life.

• Choose poinsettias with fully mature, thoroughly colored bracts. The bracts are the red, pink, yellow or speckled modified leaves that catch your eye from a distance. Avoid plants with too much green around the bract edges. 

• The true flowers of a poinsettia are the small yellow berries (also called the cyathia) in the center of the bracts. Make sure that the smaller bracts surrounding these berries are fully colored. If these secondary bracts aren't fully colored, the plants will quickly fade and lose color.

• Examine the plant's soil. It's best to avoid waterlogged soil, particularly if the plant appears wilted. Such a condition could signify irreversible root rot.

• Choose poinsettias with lush green foliage that is undamaged and free of discoloration. The foliage should be plentiful all the way down to the soil line, an indication of an active, healthy root system.

• Re-inserting the poinsettia into a large, roomy shopping bag will usually provide adequate protection for transporting the plant when it's cold and windy.

    The experienced shopper can find much more variety in poinsettias at the nursery or flower shops instead of grocery stores. "The poinsettia is a very versatile plant," says Paul Ecke Jr. of the Paul Ecke ranch, a San Diego area-based business that is regarded as the world's premiere poinsettia growing facility. "We can grow a poinsettia in a two inch pot, suitable for an office desktop, all the way to a poinsettia topiary tree several feet tall. In between we have hanging baskets of poinsettias, as well."   

 
    And there are now many more varieties beyond the familiar red-colored poinsettia, including pink, yellow, variegated and purple.

   "The 'Plum Pudding' is the first and only purple poinsettia," says Ecke, whose growing grounds produce over a half million plants for sale each year. "It's a wonderful decorator color that fits into Victorian as well as contemporary color schemes."

    No matter the variety, a little care can help a poinsettia last well through the holidays. That care starts at the retailer. "It really gets my goat when I see plants not getting watered in the stores," says Ecke. "You want to buy poinsettias from a store that is taking care of them, which includes watering them and not displaying them outdoors." He advises choosing poinsettias that have medium to dark green foliage that extends to the bottom of the pot. Steer clear of poinsettias with naked branches or yellowing leaves.

"The best way to determine if a poinsettia is still fresh is to examine the flower," says the U.C. Cooperative Extension Master Gardener Lori Ann Asmus. "However, the very bright, colorful part of the plant, which is usually red, pink or speckled, is not the flower. Those are modified leaves. The poinsettia flowers are the little, yellow bead-like parts between those modified leaves. If that yellow flower looks tight and waxy, you can be sure it's a young poinsettia plant, which will last a lot longer. If that flower, though, looks brown, bypass it; that poinsettia is past its prime. And if there is no yellow at all, move on. That plant is very old."

   A native of Mexican jungles, the poinsettia will sulk if allowed to endure temperatures below 50 degrees or not get regular waterings. In the house, the best area for the poinsettia is where it can get plenty of light, out of the way of any drafts or heating vents. A southern facing window is ideal. "And there's no need to worry about displaying poinsettias around children or pets," says Ecke. "Poinsettias are not poisonous; but don't eat them."

And if you are inclined to nurse that poinsettia through the spring, summer and fall:

• If you haven't done so already, remove any foil wrap around the poinsettia's pot to allow for drainage, putting a plate or saucer beneath to catch any excess water. 

• Poinsettias do like water; but need excellent drainage. Be sure to drain off any standing water from the saucer. 

• Although the plant may look great sitting on your dining room table, the poinsettia will thrive where it can get plenty of light, out of the way of any drafts or heating vents. A southern facing window would be ideal.
     

• In late March or early April, cut back the plant so that two buds  remain, about six inches from the base. The plant may still look elegant before you start this radical surgery, but the pruning is necessary to help it look great for next December.

• In April, place the plant - pot and all- outside in a sunny, warm area; against a south wall beneath the overhang of your house or apartment would be ideal. Keep the poinsettia watered, pruning back the branches by a couple of inches in June and August to keep the plant from getting leggy. When the red color begins to show, start feeding the plant with a fertilizer that has a bit more nitrogen in it than phosphorus and potassium. 

• In October, before the first frost, bring the plant back into the house and keep it in a dark closet or room for at least fourteen hours a day. The plant will bloom only when it has had these long "nights". And by next Christmas, you'll again be able to enjoy the striking beauty of that same poinsettia plant. Maybe.

    If all this sounds like a lot of work, it is. And the end result may not be as spectacular as the original plant's bloom. The good news: there will always be more colorful poinsettias for sale next holiday season.

And now...a song for the season: