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Nature’s Way Resources owner John Ferguson, “The Lazy Gardener” Brenda Beust Smith, and Pablo Hernandez welcome your feedback and are so grateful to the many horticulturists who contribute their expertise

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BY BRENDA BEUST SMITH (aka The Lazy Gardener) 

FLOOD-TOLERANT DELIGHTS (L TO R): swamp sunflowers, orange cannas, white hymenocallis, and my Mother’s lavender Louisiana irises.

T’is fall and gardeners’ fancy turn to . . . BULBS, of course! Most important to know if you’re new to planting bulbs here, we are NOT always like areas to the north (even far north Texas)!  

Bulbs like tulips, crocus, and hyacinths are sometimes sold pre-refrigerated, a must for inground planting (not necessary for forced bulbs). For in-ground plantings, if you can’t find these, put bulbs in paper sacks in refrigerator (NOT touching walls) for 4-6 weeks before planting. If you don’t, they will probably “blast” (bloom too soon, down close to soil). Better nurseries label/sell bulbs “pre-refrigerated.” If you don’t see that notation, ASK!

The Garden Club of Houston’s fantastic annual Bulb and Plant Mart is an absolute treasure to Houston-area gardeners, from young children to oldies like me. (Sheeze! To think I am only one year younger than the now-83-year-old Bulb Mart!) 

The 2025 Bulb & Plant Mart pre-sale is online now through Sept. 29. Mart itself opens Oct. 9-11, 2025, at The Church of St. John the Divine, 2450 River Oaks Blvd. (Same site for pickup online sales. Read all online info carefully at above link.)  

Even if you aren’t ready to buy now, the presale list with pictures will boggle your mind at how many bulbs and varieties are available (if they don’t pre-sale sell out). Review is worth the time so you can go to the sale prepared for all the incredible new bulbs available varieties, colors, flower shapes, etc. 

Every year the Garden Club of Houston produces an updated Horticultural Guide for our area to distribute free at the Bulb & Plant Mart. https://www.gchouston.org/bulb-plant-mart-info/

But If you’re in a hurry for good fall advice, the 2024 Horticulture Guide is still available online. 

FIRST MAYBE-HURRICANE: With current potential Gulf alerts already being aired and still-fresh memories of Beryl hanging around, now’s time for serious landscape and garden inventories. Especially check out those plants that are potentially flood/wind-damageable. Don’t wait until the last minute to: 

• Pick up, protect, or seriously-anchor landscape timbers and other loose materials. 
• Have a plan for moving container plants and/or outdoor furniture/lawn equipment to safer locations. Anything light enough for wind to lift needs to be anchored.  
• Put up lawn furniture and garden equipment. Better safe than sorry.

After winds die down and unwelcome waters recede:

• Replant immediately any plants washed out of beds. Mulch well.
• Hose leaves well to remove debris and water deposits. 
• If post-heavy rains, sun is very hot, protect delicate or young plants with a shade cloth. 
• Replace lost mulches. Mats of plant debris collected against fences or on lawns after flood water recedes make excellent mulches. Rake them into gardens. But . . . 
• Watch for ant mounds that sometimes float on storm water!
• Rain waters can leach out recently-applied fertilizers. Wait a while, reapply to allow plants to recover from any storm shock. 
• Perennials and newly-set-out plants may suffer dieback. Pinch the tips back and pray! 
• Don’t sigh in relief if you don’t see immediate damage. Plants may look fine at first, but die several weeks later. Keep an eye on them.
• If you have frequent storm-damaged/flooded gardens, consider these usually-storm-hardy delights for lower spots: banana trees, cannas, hymenocallis (large white native spider lily), bog lily (Texas swamp lily or Crinum americana), and Louisiana iris. These actually thrive on flooding!

Plants in beds raised 1-2′ above ground level usually recuperate faster after floods. Just be sure your border material will keep the raised soil from washing away.

Back to plants that love low spots in a yard, I’ve always wanted a red Louisiana Iris. My mother’s lavender LA Iris (above) loves my low spots. Discovered how rare the “real” ones are and as a native LA babe, want to share what I learned in this search. 

The red iris, one of Louisiana’s rarest native flowers, blooms each April in a swamp in a fragile ecosystem on carefully held private property somewhere in the general Abbeville, LA, vicinity—its only known natural habitat in the world. (Louisiana Iris Conservation Initiative)

April bloom of the Abbeville red iris in their (very well hidden) native swamp! 

Many Louisiana-TYPE iris are available and are being labeled as real ones. They’re not.  

In the meantime, REAL Louisiana Iris are still available in lavender. They bloom March – April in a variety of colors, depending on species. 

Louisiana irises are an excellent choice for naturalized landscapes, but also can be grown in raised beds if (in Greater Houston area especially) are provided regular water. They’re ideal for a garden spot designed to counter Houston’s major subsidence problems (cracked sidewalks, door that won’t shut, etc.) to drain/yet preserve excess water off the rest of the yard (https://www.natureswayresources.com/lazy-gardener-friends-588/)

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Subject: Rubber Mulch, Weed Mats, and Related Products

I was in a store the other day where a mulch made from rubber tires was being advertised as on sale. I then realized it has been a while since we talked about products made from recycled tires. I looked around and saw mats to set pots on, sort of a carpet/weed block for weed control. I even saw some in circles with a cut in them, so one can place them around trees.

First, let’s look at the source of rubber pellets to make these products. A study a few years ago found that the cause of many fish kills was the chemicals used in the automobile tires.

For years, many streams have experienced large fish kills that are called “urban runoff mortality syndrome.” The cause has finally been identified as a chemical that is found in tires. This chemical is known as 6PPD and was added to tires to slow tire degradation.

As tires wear, dust-sized particles are released, where 6PPD breaks down into 6PPD-q, which is the second most toxic chemical known to harm aquatic species. In addition to being very toxic to fish and other aquatic species, a recent study found that this chemical can bioaccumulate in mammals, causing inflammation and increasing liver triglyceride levels in mice. https://pubmed.ncbi.nlm.nih.gov/36716866/

Many gardeners enjoy having a pond or other water feature as part of their gardens filled with fish. Most of us do not like mosquitoes. Fish and other aquatic life eat mosquito eggs, reducing their population. Less fish and aquatic life means more mosquitoes.

While at the store, I looked at the sale price of $6.99 per 0.8 cubic feet bag, which did not seem too bad until one does the math. A standard mulch bag (Soil and Mulch Producers Association standards) is two cubic feet. That means to get enough rubber mulch to equal a standard-sized bag, it would cost about $9.00 per bag. A very high-quality aged Native mulch is only $8-10/bag. If we compare this to bulk prices, to get enough bags of toxic rubber mulch to equal a cubic yard, it would cost $236 per cubic yard! 

Another study in the journal Chemosphere back in 2012 found that recycled rubber tires used on playgrounds and pavers contained many hazardous substances. These include PAH’s, phthalates, BHT, phenols, benzothiazole and its derivatives, among other chemicals. As the temperature gets hotter, these toxic chemicals turn to gas much quicker.

As the black color of the mulch absorbs sunlight, the rubber gets very hot, and this increases the heat index (gets so hot it can burn plants), it also heats the soil beneath it, causing much more rapid evaporation, drying out the soil. The higher heat indexes stress the plants, leading to higher insect and disease issues. As the heat index increases, chemical reactions proceed at a faster pace. USDA tests show excessive leaching of Zinc, causing severe phytotoxicity in acid soils, and will contaminate soils with other tire components.  

Other tests around the world have confirmed USDA research and have shown that as little as 5% ground tire rubber in potting media is toxic to petunias and Impatiens [“Communications in Soil Science and Plant Analysis, 27 (13 & 14), 1996]. Tests at Colorado State University found that growth of geraniums grown in media with tire chips were lower than with traditional media [HortScience 32(4):674-676, 1997]. Additional research at Iowa State and Mississippi State has also found decreased growth and other problems when used in a potting mix with Geraniums and Poinsettia plants [HortScience, Vol 32(5), August 1997]. Some of the dyes used to color tire chips may be toxic. 

Several reports of spontaneous combustion when applied too thickly. I witnessed this a few years ago up in Washington state, where the highway department had used tire chips to backfill an area on an overpass for a road. The thought was that the high permeability of the mulch would let rainwater move through without washing out the sides of the slope. The road was shut down by the fire department as the tire mulch filler had gone into spontaneous combustion. Water did not put it out and actually made matters worse.

Rubber tire mulch has a higher density than most soils. Hence, it often sinks into the soil due to its higher density when compared to organic mulches. This requires frequent replacement. 

Additional information on the toxicity and dangers of rubber tire mulches continues to be exposed. Contrary to the marketing claims that chemicals do not leach from rubber mulch, chemical analysis of leachate from rubber tire mulch has been found to contain aluminum (Al), cadmium (Cd), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), selenium (Se), sulfur (S), in addition to zinc (Zn) which is 2% of a tire’s mass. Studies have also found that if a tire has been exposed to other contaminants, such as lead or other heavy metals, the tire rubber will absorb them and then release them in the leachate as well. 

Other researchers have found that rubber tire mulch can leach various plasticizers and accelerators that are used during tire manufacturing. High concentrations are known to be harmful to human health, from skin and eye irritation to major organ damage and even death. Long-term exposure can lead to neurological damage, cancers, and mutations. 

Some toxic materials in rubber mulches bio-accumulate, such as 2-mercaptobenzothiazole. In addition to its known human health effects, it is highly persistent in the environment and acutely toxic to aquatic organisms. 

Polyaromatic hydrocarbons (PAHs) are also used as softeners and fillers and have repeatedly been shown to poison aquatic life. One study found that the PAH leachates became more toxic after two years than at the beginning of the study.

When iron (Fe) is exposed to excess zinc (Zn), it forms the mineral franklinite (ZnFe2O4), which decreases the availability of both metals to plants. This has been proposed as one of the mechanisms as to why “rubber tire” mulch is so toxic to plants. This mineral can also act as a cementing agent, gluing soil particles together, creating hardpan. Zinc (Zn) is used to make steel belts and in other components.

I was reading another study a while back from Yale University, where they were testing the crumb rubber that is used to make rubber mulch and used in sports fields with artificial turf. The crushed tires are used as padding under the synthetic turf used on sports fields.

The research found over 100 different compounds in the rubber, and less than 50 had been tested for toxicity. Of those tested most were carcinogens or irritants. 

In another set of tests, they found 96 chemicals in 14 samples. Of these, 47 had never been tested for safety or health effects. Of these chemicals, 40 are known irritants and 12 are respiratory irritants, of which some cause asthma, and 10 are known carcinogens. 

The researchers stated that the shredded tires contain a veritable “witches brew” of toxic substances, and they are a hazardous waste.

Health data has also been collected by the sports department at the University of Washington, and they found that 124 soccer players have cancer, and 85 are goalies who spend more time on the ground than other players.

The study was commissioned by the organization, “Environment and Human Health“. They (Nancy Alderman) stated children should never be allowed to play on synthetic turf.  

I believe that this should extend to playgrounds that use rubber mulch, and children should not be allowed to play on them.

New research from Oregon State University has found that small particles from tires inhibited growth and caused adverse behavioral changes in aquatic ecosystems.

These microplastic tire particles leached synthetic rubber, oils, filling agents, etc. into the environment. Journals Chemosphere and Journal of Hazardous Materials 2022

Tire mulch also leaches large amounts of zinc (Zn) into the soil causing a chemical imbalance in the soil that leads to many gardening problems.

Rubber mulch is broken down by microbes like any other product even if very slowly (remember microbes can break down granite rocks into soil), rubber is easy by comparison. The rubber encourages species of bacteria that break down rubber and rubber-like products in your home to multiply. The additives in tires to prevent bacterial decay (which are toxic chemicals) are broken down by white and brown rot fungal species that live in soil. This same decomposition is what releases the toxic chemicals in tires.

However, the rubber tire mulch does kill many species of good microbes that kill insects and prevent disease. The toxic chemicals in the tires will also kill beneficial insects that help control pests. Hence one frequently sees increases in pests and disease.

Another issue with rubber mulch is the odor. This may be a matter of opinion, but most people find that rubber mulch starts to stink as it gets hotter. On a hot day, it has a strong stench. As tires are ground up into chips, the amount of surface area is greatly increased, and all the new surfaces are freshly exposed, allowing for maximum odors to be released. Many people get sick from just being in the sales area of a store selling new tires.

As rubber mulch heats up, it releases toxic gases such as volatile organic compounds (VOCs) and another class of chemicals called polyaromatic hydrocarbons (PAHs). These gases have been found to cause irritation of the nasal and respiratory passages, central nervous system damage, depression, headaches, nausea, dizziness, eye and kidney damage, and dermatitis. Hence, ground tires should never be used in an enclosed area or indoors. These effects would be even worse in areas of high air pollution (i.e., Houston).

It is true that rubber mulch will not mat down as easily as organic mulches, since the beneficial microbes that create soil structure, prevent insect and disease problems, cannot live in it. 

As to mold, I have seen many tires used on piers and boat docks covered with algae. I have also seen tires used as planters covered with what appears to be mildew and mold. Mildew and mold will grow on about any surface if moisture is present, unless it is too toxic and something kills them. 

During the drought of 2011, there were many large wildfires all over Texas and other areas of the country. Following this fire season, several universities started doing studies on the flammability issues associated with all types of mulches. Hence, they also tested rubber tire mulch.

Ignition Results

• Match ignition of Rubber Chipped Mulch occurred every time in later demonstrations, along with the Dyed and Shredded Hardwood Mulch
• Fire in Chipped Rubber Mulch:
• Gives off toxic fumes
• Cannot be extinguished with water; in fact, water spreads the flames 
• Extinguished by beating out with a shovel

Products from Rubber tires, like mulch, should never be used in a landscape. 

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