Safety of Wood Products in the Garden

Safety of Wood Products in the Garden

Despite a sharp increase in costs recently, wood products remain a common landscape and garden material. They can be used for building structures, such as arbors and sheds, or for hardscapes and garden accessories, like raised vegetable garden beds or landscape timbers used for edging. Many homeowners may be confused on the safety of using certain wood products, especially around plants grown for consumption. This article hopes to explain the various options and the known safety concerns.

wooden garden box

Raised beds are a common use of treated lumber in the garden. Credit: Molly Jameson/UF IFAS

Gardeners seem to be mostly concerned with the safety of using preserved wood products around food plants. Pressure-treated lumber is usually suggested whenever the material will be exposed to the elements and especially when in contact with the soil. Non-treated lumber, while free of any preservatives, will simply not last as long in the landscape, especially in Florida where we have a long growing season, are wet, and have lots of organisms – termites, fungus, etc. – that love to break down wood. If the wood is in direct contact with the soil, such as in a raised bed garden, you can expect non-treated lumber to last a year, maybe two, compared to three to five years with pressure-treated lumber. Wood products used for structures not in contact with soil can last significantly longer but, even then, non-treated products will need to be protected with sealers or paints to extend their longevity.

To address the safety of pressure-treated wood products, the wood products industry, and the federal government, in 2004, phased out the use of potentially hazardous chemicals used in the process – namely arsenic and chromium. Wood products preserved with these compounds were either chromated copper arsenate (CCA), ammoniacal copper arsenate (ACA), or acid copper chromate (ACC). Since 2004, much of the lumber available at hardware stores is micronized copper azole (CA) or alkaline copper quaternary ammonium (ACQ). The abbreviations for each are usually found on the little label stapled on to the lumber. So, while copper used to prevent fungal damage is still a component of pressure-treated lumber, the arsenic and chromium used to protect the wood from insect damage has been removed. Railroad ties, sometimes still in use and for sale, are much more toxic than even the older pressure-treated products because of the use of creosote and other oil-based compounds to preserve the wood.

a stack of wooden boards

Preserved wood products contain the preservation method on the tag stapled to the product. Credit: USDA Forest Products Lab

By removing these potentially hazardous compounds from pressure-treated wood products, gardeners should expect no adverse effects from it’s use. A Human and Ecological Risk Assessment of ACQ treated wood that was done in 2007 found exposure levels well below health benchmarks when directly contacting the wood and even with some ingestion of the material, such as contacting the wood and putting hands directly in mouth.

Even though these hazardous materials have been removed, there are still some precautions you should take when using pressure-treated lumber. These precautions include wearing a mask when cutting the lumber and not burning the lumber. This is to prevent inhalation of the chemically treated sawdust or smoke. It’s also not recommended to compost pressure-treated lumber since the chemicals can affect the microbes in your compost pile.

For those still concerned with the use of pressure-treated wood products around food crops, there are other options. In addition to using non-treated wood products or a plastic liner to separate the pressure-treated lumber from your edible garden plants. There are many other materials that can be used instead. Concrete blocks or other stone materials can be a good option. Logs from cut trees, although will rot like non-treated lumbers, can add a natural type of look to the garden.

garden beds

Stone, metal, and concrete blocks are good alternatives to lumber. Credit: Mark Tancig/UF IFAS.

For additional information on pressure-treated lumber, visit this Clemson University website – If you have any questions about the use of wood products in the garden or on how to build a raised bed garden, contact your local UF/IFAS Extension office.

Yay for Yarrow

Yay for Yarrow

Gardeners delight in finding a versatile and resilient landscape plant, especially one that is easily shared. Unfortunately, when a plant checks off those characteristics, it usually finds itself on the invasive species list (see IFAS Assessment). Well, in the case of yarrow (Achillea millefolium), we get a tough plant that is easily propagated, has attractive blooms and foliage, attracts butterflies, and is considered native! As I’ll discuss below, it doesn’t come totally flawless.

Yarrow, in the Asteraceae family, is a great addition to the landscape.

Yarrow is considered a cosmopolitan species. It is found across the entire northern hemisphere and there has been a lot of mixing of native and introduced plants, causing much confusion amongst botanists. It is currently considered a single, though complicated, species. Much of the mixing is due to its history with man, being carried along all sorts of expeditions, even the mythical character Achilles, where the plants genus name comes from. The species name comes from the finely divided leaves – like a thousand leaves. It is in the daisy and sunflower family, called the Asteraceae, or composite family, due to the flower heads being composed of many individual flowers.

The cluster of flowers over the feathery leaved foliage is what makes yarrow stand out. The classic yarrow is white-flowered, but breeders have developed many cultivars in an array of colors, including red (‘Rosea’ or ‘Paprika’), pink (‘Cerise Queen’), purple (‘New Vintage Rose’), and yellow (‘Gold’ or ‘Lemon’). Yarrow is also great for its drought tolerance and has few pests or diseases that bother it. It is even reported to be deer resistant! It can be propagated by seed and is easily divided.

Yarrow ‘Paprika’ is a commonly found yarrow cultivar. Source: Timeh87, Creative Commons license.

The common yarrow shows off beautiful white blooms over the feathery foliage. Credit: Rachel Mathes, UF/IFAS.

With all these great attributes comes one potential problem – it is considered toxic to dogs, cats, and horses. Yarrow contains a toxic alkaloid, called achilleine, that can poison some mammals. So, if you have an adventurous pet that likes to chew on random plants, then you may want to skip adding yarrow to your landscape. Achilleine is the same compound that has led it to be used by humans for centuries as a blood clotting agent. Achilles was said to have carried yarrow to the battlefield in Troy for his soldiers and the plant has been known as herba militaris and soldier’s woundwort. Of course, always consult a doctor for medical advice!

While not a good choice around Fido, yarrow can be a great plant for Florida gardeners. For more information on growing yarrow, see this Ask IFAS publication and this profile from Evergreen State University. You can also contact your local county extension agent for additional information on gardening and more.

Update on Citrus Greening in North Florida

Update on Citrus Greening in North Florida

The Asian citrus psyllid, Diaphorina citri, spreads the bacterium responsible for citrus greening. Photo by Michael Rogers, UF/IFAS.

Asian citrus psyllid, Diaphorina citri. UF/IFAS/Entomology Photo: Michael Rogers.

In late 2016, as many of us were enjoying the harvests from our backyard citrus, a bacterial plant disease that can affect all citrus, citrus greening, was widespread in central and south Florida but had not made it this far north. That year, the vector, the insect that spreads the disease from tree to tree, had been found in Leon County and a few other surrounding Panhandle counties, but the disease had not. By mid-2017, the disease had been confirmed in Franklin County and we hoped that our cooler temperatures could keep the insect and disease at bay. Well, I regret to inform you that the disease has also now been confirmed in Leon County, growing in a residential yard in Tallahassee. Now that it is confirmed in non-coastal (and cooler) north Florida locations, I thought a review of the signs and symptoms – as well as what to do with your tree if you suspect or confirm greening – would be helpful.

The tricky part about diagnosing citrus greening is that it has symptoms that look very similar to soil nutrient deficiency symptoms, especially when first infected. This is a good time to mention that citrus require certain micro-nutrients for optimal growth and a citrus-specific fertilizer product should be used when applying fertilizer. Both the disease and certain nutrient deficiencies cause yellowing of the leaves. With greening, the yellowing is typically blotchy and/or not in any particular pattern. Nutrient deficiencies typically cause unique patterns of yellowing, such as a V-shape or artistic-like symmetrical patterns on each side of the leaf’s midvein. The soil’s acidity, or pH, can also cause some nutrients to not be taken up by the plant even if they are present. Soil testing, available from your local UF/IFAS Extension office, and scheduled fertilizations with a citrus-specific fertilizer can ensure that nutrients are not to blame for the discoloring of leaves. More advanced stages of the disease cause such symptoms as leaf drop, fruit drop, lop-sided fruit, uneven inner fruit cores, and reduced fruit quality.

Citrus greening symptoms of the fruit. Photo by Brooke Moffis.

Citrus greening symptoms of the fruit. Photo by Brooke Moffis.

A more obvious sign of potential problems for your citrus are the presence of the insect vector, the Asian citrus psyllid. This is a tiny little insect that goes from one leaf to the other sucking up plant saps for food and unknowingly spreading the bacterium responsible for citrus greening. You can monitor for them by looking closely at the new flushes of growth. If the psyllids are present, you will likely notice most their small, peach-colored eggs and/or white, waxy secretions. If found, it doesn’t necessarily mean that your tree has greening, but you will want to minimize the chance that they could carry it to your tree. The psyllids can be treated with pesticides, ranging from the less harsh options (horticulture oils, neem oil, kaolin clay) to the more hardcore stuff (malathion, carbaryl, imidacloprid). Of course, always read the label of any pesticide before use and/or consult a qualified landscape professional for assistance.

Blotchy leaf symptom of citrus greening. Photo by Jamie D. Burrow.

Blotchy leaf symptom of citrus greening. Photo by Jamie D. Burrow.

If you suspect your tree is infected, a diagnostic test can be performed by UF/IFAS plant pathologists at the North Florida Research and Education Center (NFREC) in Quincy to confirm. The test does cost $50, which may seem a little steep, but it’s an expensive lab analysis to run and may be worth piece of mind.

If citrus greening is confirmed in your tree, the right thing to do, unfortunately, is to remove and burn the plant material as there is no known cure. While the Florida Department of Agriculture and Consumer Services (FDACS) doesn’t have any removal requirements for infected dooryard citrus, tree removal is best to prevent additional spread of the disease to other trees, especially those grown by commercial producers in our area. This may seem drastic but eventually the health of the tree and quality of the fruit will decline to a point where you will want to remove it anyway. Don’t forget that movement of any citrus plant outside of the state is prohibited for the very reason of preventing spread of citrus diseases.

You may be asking, “Is it okay to replace it with another citrus tree?” The answer is yes you can, but you do risk re-infection and will want to be monitoring the new planting.

You may also be thinking, “What is going to happen to Florida citrus?” That’s a question that many researchers at UF/IFAS are trying to answer. There is some hope that intense irrigation and nutrient management, as well as specific pruning practices, can help infected trees continue to be profitable for commercial growers. Recently, UF/IFAS researchers were awarded several grants to try and figure a way out of this problem. Some of the lines of research focus on exploring the resistance found in different citrus varieties, including an Australian lime that appears to be greening resistant. This could potentially be used as a future rootstock. Another approach is to try and treat the plants with a particular peptide that would prevent the disease from binding in the insect’s gut. Isn’t that amazing?

Until a fix is found, we should be monitoring for this disease in our area and taking steps to reduce its presence through controlling the psyllids and removing infected trees. If you suspect a tree has greening, please contact your local county Extension office to review the symptoms and discuss your options.

Much more information on citrus greening is available at the following Ask IFAS website: and from this 2017 article –

Bzzzz, It’s Mosquito Season

Bzzzz, It’s Mosquito Season

Now that we’re getting plenty of rain and the temperatures are nice and toasty, our nemesis to enjoying the outdoors is back in full force. Yes, I’m talking mosquitoes, the reason for inventing window screens! If you’re gardening outside these days, you’ve probably been annoyed by one of the many mosquito species that occur in our area. Many of these mosquitoes are native species that play an important role in the food chain, feeding many aquatic and terrestrial wildlife, but some of them, like the daytime biting Asian tiger mosquito, are invasive species that were accidentally introduced. While mosquitoes are an important food source to more charismatic critters, they are annoying and can spread disease, and so we can benefit by reducing their presence.

The Asian tiger mosquito, another annoying invasive species. Photo credit: Susan Ellis,

In addition to the age-old advice of draining any standing water, there are other control methods that can be very effective at reducing the mosquito population. One of the most effective and least-toxic options is the use of Bti products. These products come in granular or “donut” forms with the smaller granules being best for various uses around the home and the dunks/donuts for larger areas of standing water like ponds. These Bti products are considered a type of biological control since it is a species of bacteria, Bacillus thuringiensis israelensis to be precise, that causes mosquito, blackfly, and fungus gnat larvae to perish as they wiggle around and grow into their pupal stage. Because it only affects a narrow range of species, it is considered a selective pesticide that does not cause harm to non-target species, such as bees, birds, butterflies, frogs, lizards, and other desirable garden visitors. Bti can be sprinkled into rain barrels, bird baths, bromeliads, gutters, and other places where water may stand more than 5-7 days, the amount of time needed for mosquito eggs to develop into adults.

Bti granules prevent mosquito larvae from becoming biting adults. Photo by: Mark Tancig, UF/IFAS.

If considering other methods of mosquito control, such as the use of foggers, keep in mind that many of the pesticides used to control adult mosquitoes are not selective products and can kill the pollinators you may be trying to invite to your garden. Additionally, planting citronella plants, eating copious amounts of garlic, wearing repellent bracelets, or using ultra-sonic devices or cell phone apps has not been shown to repel mosquitoes so stick to what is known to work.

For a more enjoyable mosquito season, keep the window screens tight, wear long pants and sleeves and use appropriate repellents when outdoors, and do your best to minimize standing areas of water. If you have questions about mosquitoes and their control, visit the UF/IFAS Florida Medical Entomology Lab website ( and browse the many resources available.

It’s Hot, Consider Planting a Shade Tree

It’s Hot, Consider Planting a Shade Tree

Spending time outdoors during the Florida summer is not for the faint of heart. It’s hot! And it’s humid! Just moving around outside for a moment in the early morning causes you to break out in a sweat. Most evenings, even after the sun is low in the western sky, but there’s still enough light to enjoy the outdoors, the sweat doesn’t stop. A Floridian’s only hope is that nearby, there is a large shade tree to take cover under. In north Florida, there’s nothing more inviting than a huge live oak draped in Spanish moss for a drink of ice water and a slight breeze. If you don’t have such a spot, start thinking about planting a shade tree this winter!

A large live oak is great for shade! Credit: Dawn Reed.

In north Florida, we have many options to choose from, as we live in an area of the United States with some of the highest native tree abundance. Making sure you get the right tree for the right place is important so make a plan. Where could this tree go? Is there plenty of space between the tree and any structures? You’ll want to give a nice shade tree plenty of room – 20’ to 60’ away from structures and/or from other large trees – to grow into a great specimen. Be sure not to place a large tree under powerlines or on top of underground infrastructure. You can “Call 811 before you dig” to help figure that out. If space is limited, you may want to consider trees that have been shown to be more resilient to tropical weather. Also try and place the tree in a way that provides added shade to your home. Deciduous trees planted along your home’s southeast to southwest exposure provide shade during the summer and let in the sun during the cooler winter. However, be careful that the tree doesn’t grow to block the sun from your vegetable garden!

A density gradient map of native trees in the US. Notice where the highest number occur. Credit: Biota of North America Program.

Here are some ideas for shade trees, those trees that are tall (mature height greater than 50’) and cast a lot of shade (mature spread greater than 30’). All of these are native trees, which have the added benefit of providing food and shelter to native wildlife.

  • Red maple (Acer rubrum)
  • Pignut hickory (Carya glabra)
  • Green ash (Fraxinus pennsylvanica)
  • Tulip poplar (Liriodendron tulipifera)
  • Southern magnolia (Magnolia grandiflora)
  • Sycamore (Platanus occidentalis)
  • Shumard oak (Quercus shumardii)
  • Live oak (Quercus virginiana)
  • American elm (Ulmus americana)

It’s best to plant during the winter and follow good planting practices.

Even with this young sycamore, you'll be made in the shade

Even with this young sycamore, you’ll be made in the shade. Credit: UF/IFAS.

While it may take a while for you to relax under the shade of your tree, they can surprise you in their growth and, as they say, there’s no time like the present. If you have questions on selecting or planting shade trees, contact your local UF/IFAS Extension office.