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Does Excess Car Exhaust Damage Gardens?

“How would a parking lot with 16 stalls [and the car exhaust] next to my garden interfere with plant photosynthesis?” Sylvia of Belle Plaine, Minnesota

Answer: It is a very interesting question. Car exhaust contains gasses that are helpful to plants and photosynthesis and some that are harmful. Car exhaust is also everywhere, especially if you live in an urban area, though the increase in hybrid and electric cars is reducing car fumes. Still, nearby fumes may have some impact. Here is a breakdown of exhaust components from a standard car that runs on gasoline followed by the potential impacts of those gasses on plants and photosynthesis.

U.S. Environmental Protection Agency estimates of average passenger car emissions in the United States for April 2000
Component Emission Rate Annual pollution emitted
Hydrocarbons 2.80 grams/mile (1.75 g/km) 77.1 pounds (35.0 kg)
Carbon monoxide 20.9 grams/mile (13.06 g/km) 575 pounds (261 kg)
NOx 1.39 grams/mile (0.87 g/km) 38.2 pounds (17.3 kg)
Carbon dioxide – greenhouse gas 415 grams/mile (258 g/km) 11,450 pounds (5,190 kg)

(Click here for more exhaust gas details from Wikipedia.)

Carbon Dioxide and Plants

Here is the equation for photosynthesis as defined in Brittanica: 6CO2 + 6H2O → C6H12O6 + 6O2. Carbon dioxide is essential for photosynthesis, which is why it’s good to plant as many trees and garden plants as you can to help reduce this most abundant greenhouse gas. Plants take CO2 out of the atmosphere! Trees and large plants are highly effective photosynthesizers due to their sheer size, and grasses are super photosynthesizers, so consider planting a row of ornamental grasses (click here for some great ornamental grass options) or some trees and shrubs nearby to combat local CO2.

Carbon Monoxide and Plants

I found a technical overview of carbon monoxide in the atmosphere, which stated: “Carbon monoxide does not poison plants since it rapidly oxidizes to form carbon dioxide which is used for photosynthesis.” So, it is not harmful to plants either.

Nitrogen Oxides and Plants

Nitrogen oxides (NOx) contribute to smog, which blocks the sun’s rays, and acid rain, which is harmful to plants, so in excess, NOx is harmful to plants. Still, there is so much NOx in urban areas, the amount produced by the cars in the parking lot next to you would be negligible. On the plus side, you can plant nitrogen-fixing plants, such as plants in the pea and bean family as well as bayberry shrubs, to help with local NOx. These plants actively remove atmospheric NOx and convert it into a soil-borne form of nitrogen that benefits plants.

Hydrocarbons and Plants

In general, petroleum hydrocarbons are toxic to plants in high quantities, especially if they make their way into the soil (oil- or gasoline-contaminated soils). The cars nearby do emit hydrocarbons but in much lower quantities, so they should not be a problem for your garden.

As stated earlier, I recommend planting a tree, shrub, or ornamental grass buffer between your garden and the parking lot. Tough nitrogen-fixing options would be ideal! In addition to bayberry, try the following options suggested by my colleague Russell Stafford: “Outstanding legumes for perennial borders include false indigo (Baptisia spp.), wild senna (Senna spp.), yellow lupine (Thermopsis spp.), lupine (Lupinus spp.), and leadplant (Amorpha spp.).  The roster of leguminous shrubs is also lengthy, boasting such standouts as bush clover (Lespedeza spp.)…” (Click here to read the full article.)

For general greenhouse gas information, I also recommend that you read this informative piece from the EPA about greenhouse gasses and their management (click here to read it).

I hope that this information is helpful!

Happy gardening,

Jessie Keith

Black Gold Horticulturist

Cooling Garden Water Features

I snapped this photo of a hummingbird enjoying my cooling water fountain. (Image by Mike Darcy)

The sight and sound of water in a garden can lift it to a new level. When I am in a garden and hear or see water, it can, almost instantly, create a calming, serene atmosphere. Whether it is a simple birdbath, a splashing fountain, a flowing stream, or a pool, water gives a garden something more.

Garden Water Features for Birds

Robins happily splash in a garden birdbath.

Of course, fountains and birdbaths in gardens provide many wildlife benefits in addition to the pleasure that they give us. Especially this summer in the Pacific Northwest, and many other western areas as well, these water features may provide the only fresh sources of water for birds and other wildlife.

In my own garden, I have several birdbaths, and they are in constant use throughout the day. I am often amazed at not only the number of birds we get daily but the different kinds of birds. (Note: I am always diligent in emptying the birdbaths out every morning and refilling them with fresh water so as not to spread any disease. It also prevents a breeding area for any mosquito larvae.) If birds have become accustomed to a birdbath in your garden and are dependent on it for water, please be aware of the need to keep it filled, especially during hot, dry times. In many urban settings, sources for water may be very limited, so all gardeners in cities should have water for birds and other wildlife.

Garden Fountains

Wall fountains are space-saving, cooling, and beautiful.

In addition to birdbaths, many gardeners add water features with running water. The water movement can be brisk or slow, depending on the wishes of the gardener. I recommend some water movement as a preventative to stop mosquitos from laying eggs because mosquitoes do not lay eggs in running water.

In my garden, I have a very large glazed pot that originally was meant to be a planter, but it has been converted to a fountain. It has become a focal point in the garden, and birds love it. Hummingbirds often land on the rim, and let the gentle flow of water run over their feet. It is also not unusual to see our black lab, Cody, use it as a source for drinking, so this fountain has become multi-use when the original purpose was as a piece of garden art.

Garden Streams and Waterfalls

Garden waterfall features with pumps can be large and elaborate or small.

We have neighbors that have built a short, shallow running stream in their garden. It is delightful to sit by, watch the water as it flows, and hear its sound. It creates a very peaceful and tranquil setting. Many water features are considered garden art and an integral part of the garden. This is one of them. Then, there are others that can function as art and for utility.

Waterfalls in gardens can create a different effect, often with sound and sight taking one mentally to a different place. Adding koi, or other colorful fish, can enhance the experience. Even small fountains now offer choices as to the desired flow. With many pumps, the flow of water can be regulated to a gentle flow or one that is more rushing.

Our dog, Cody, also enjoys our garden fountain! (Image by Mike Darcy)

When visiting other gardens, it is always a treat if they have birdbaths, fountains, or other water features. Gardeners can be innovative with their plants as well as their water features. It is a good idea to visit other gardens with water features for ideas and options for your own garden. Talk with the garden owners, because they can give advice and perhaps prevent any pitfalls that you may not have considered. Once you know what water feature you want, check with a professional to review other important factors other than just plugging in the pump.

What Are Some Good Fall-Blooming Bulbs?

Red Spider Lily (Lycoris radiata) is a very pretty bulb the blooms in late summer and fall.

“What are some good fall-blooming bulbs? I can never seem to find any that bloom in the fall. Thanks.” Question from Brenda of Peterson, Iowa

Answer: There are quite a few fall bulbs that will grow well in your USDA Hardiness Zone 5a garden. Here are some of the best. Follow the links on each plant name for good bulb sources!

Fall Bulbs for Midwestern Gardens (Zone 5)

Red Spider Lily (Lycoris radiata) and Yellow Spider Lily (Lycoris aurea) are two South African surprise lilies that bloom from late summer to fall and are hardy to zone 5. They look really lovely together and bloom on tall naked stems that give them a striking look in the garden.

Fall Crocus (Crocus spp.) come in all different colors and forms and look very much like their spring counterparts. Most are very hardy and some, such as Crocus kotschyanus, naturalize or spread in beds and lawns. One that I highly recommend is the saffron crocus (Crocus sativus) from which you can collect your own saffron! (Click here to learn more about growing saffron.)

Colchicum (Colchicum spp.) comes in lovely shades of pink, white, and lavender, and most are quite hardy. They look very much like giant crocuses, but they are surprisingly unrelated. The double-flowered ‘Waterlily‘ is especially pretty. The only downside is that these plants are toxic, so refrain from planting them if you have small children or pets that might handle or consume them. (Click here to learn more about Colchicum toxicity.)

Fall Snowflakes (Leucojum autumnale (Acis autumalis)) is a rare but wonderful fall-blooming bulb from the Iberian peninsula that is hardy to your zone. Its white, bell-shaped flowers look very springy and mingle well with other perennials.

Happy gardening,

Jessie Keith

Black Gold Horticulturist

Can Watermelons Be Grown in Containers?

Here is a watermelon that I grew in a pot a couple of years ago.

“Can watermelon vines be grown in containers?” Question from George of Hagerstown, MD

Answer: Watermelons can be grown in large containers if you choose a compact variety. Here are my recommendations regarding potted watermelon culture.

Growing Potted Watermelons

First, choose a more compact, short-vine watermelon variety suited for container growing. ‘Cal Sweet Bush‘, a 2019 AAS award winner, has excellent melons and vines that do not take over, and ‘Bush Sugar Baby‘ is another small-vined type with tasty melons. Next, choose a large container that’s between 18 to 24 inches. There must be holes at the bottom for drainage. Plastic or glazed containers hold water better in the heat of summer. Fill the pot with quality, porous potting soil that holds water well. I would choose Black Gold Natural & Organic Raised Bed & Potting Mix. Place the pot in a spot where it gets full sun, and the vining stems can hang down and spread a little. Patios or open garden areas work well for large potted vegetables like this.

Plant one or two watermelons in the pot in spring after the threat of frost has passed. Keep the soil moist. When the vines have reached a good size in summer, water daily in the absence of rain. Fertilizer well from the beginning. A good slow-release fertilizer formulated for vegetables is ideal. Be sure to follow the manufacturer’s application instructions.

Melons should start to appear by late July or August.

Happy melon growing!

Jessie Keith

Black Gold Horticulturist

Why Are My Cucumbers Bitter?

“I am growing the same cucumbers this year as last year.  Every cucumber this year looks beautiful but tastes very bitter and is inedible.  I believe I am providing adequate water, though due to the heat the plants still wilt during the day. What can I do to improve the flavor? ” Lisa of Marietta, Pennsylvania

Answer: There are two things that can cause cucumbers to become bitter – the cultivated variety and environmental stress (heat stress, water stress, or disease). A great Oregon State University (OSU) article on the subject quotes the vegetable breeder, Jim Myers of OSU. He explains that the source of cucumber bitterness is caused by the natural plant chemical, cucurbitacin. It exists in high quantities in the leaves and stems of cultivated cucumbers. During stressful summers, concentrations can build up at different levels in the cucumber fruits as well; often at the blossom end. What’s odd is that sometimes a single plant may have some bitter fruits and some nice-tasting cucumbers, so taste each one to double-check before composting. The same plant may also produce sweeter fruits as growing conditions become better.

Non-Bitter Cucumber Varieties

Some varieties tend to reliably produce sweet cucumbers, even under stress. Here are five excellent cucumbers that resist bitterness.

  1. ‘Katrina‘- The crisp, seedless, Beit-Alpha-type cucumber is also very disease-resistant and stays sweet.
  2. ‘Jibai Shimoshirazu’ – This heat-tolerant, Japanese snacking cucumber never gets bitter!
  3. ‘Green Light‘ – There is a reason that this cucumber was a 2020 All-America Selections winner. Its fruits are crisp, sweet, prolific, and resist bitterness.
  4. ‘Marketmore 97‘ – This classic, disease-resistant cucumber is known for its ability to stay sweet, even when stressed.
  5. ‘Unagi’ – After reading about this one, I plan to grow it next year. Its hybrid cucumbers are crisp, sweet, and very prolific.

I also recommend that you watch the video below to learn how to grow cucumbers to perfection. I know that it can be difficult in years where high heat, drought, and even excess rain are problems, but the video contains some good growing tips.

Happy gardening,

Jessie Keith

Black Gold Horticulturist

Can I Grow Peonies Down South?

‘Coral Charm’ is a peony that grows better down South, and it is one of my favorites!

“I live in south Georgia and I would love to plant peonies, but I was told by a local nursery that they can’t survive here because we don’t have cold enough winters for them to reset, is this true?” Question from Ladonna of Naylor, Georgia

Answer: It is partially true. The most popular peonies in the US are common garden peonies (Paeonia lactiflora). The large, bushy plants produce loads of big, late-spring flowers and are hardy to USDA Hardiness Zones 3-7 (sometimes 3-8b), so you are on the edge of their hardiness. They do need winter cold for several months to produce blooms and survive in the long term, but Naylor, Georgia (USDA Hardiness Zones 8b) is cold enough to sustain some peonies. If you want to be on the safe side, there are other peonies that can survive with even less winter cold. This includes some tree peonies (Paeonia species and hybrids, varying zones, sometimes down to zone 9), and Intersectional (ITOH Hybrids (Zones 4-9), which are hybrids between common and tree peonies.

Peonies for Southern Gardeners

Here are seven good herbaceous peony varieties for southern gardens.

  1. ‘America’ (Zones 4-8b)- a single, red herbaceous peony that is award-winning and has HUGE blooms
  2. ‘Coral Charm‘ (Zones 3-8b) – a semi-double coral-pink award-winner (one of my favorites!)
  3. ‘Felix Crousse‘ (Zones 3-8b) – an herbaceous heirloom (1881) with fragrant double-red blooms
  4. ‘Festiva Maxima’ – an herbaceous heirloom (1881) with fragrant double-red blooms
  5. ‘Red Charm’ – an herbaceous peony with fragrant, deepest red, double blooms
  6. ‘Scarlet O’Hara’ (Zones 4-9) – Another exceptional single-red peony
  7. ‘Shirley Temple’ (Zones 3-8b) – a beautiful double peony of palest cream-pink

Click here to read more about caring for peonies, and click here for a full list of peony nurseries approved by The American Peony Society! 

Happy gardening,

Jessie Keith

Black Gold Horticulturist

Growing Gorgeous Gladiolus

There is nothing more beautiful in the summer than sword lilies (Gladiolus hybrid) in a vase or the garden. Their stately stalks of glowing, fragrant flowers come in an array of colors that just can’t be beat! Most gardeners grow them for cut flowers, but glads can also be carefully worked into summer flower borders for floral impact. There are also compact types suitable for border edges and even containers!

A Short History of Garden Gladiolus

Gladioli have bulbous root structures called corms that can easily be dug in fall for winter storage where they are not hardy.

Though Gladiolus species exist across much of the Old World, most garden gladioli originate from complex hybrids of numerous South African species–South Africa being the world center of Gladiolus diversity. World travelers and collectors brought the first South African specimens to Europe in the mid-1700s, and the earliest hybrids appeared by the early- to mid-1800s. Commercial nurseries continued developing their own hybrids (and do to this day), and the flower took off in popularity. By Victorian times, when meanings were attached to every flower, red gladiolus flowers signified love and passion, while pink ones meant femininity and motherly love.

Planting and Caring for Gladiolus

Byzantine sword lily is a beautiful species that is quite hardy.

Start planting gladioli a week after one’s last frost date (click here to determine your last frost date). Choose a sunny spot with fertile, well-drained soil that’s high in organic matter. To keep waves of these short-season flowers blooming from early summer on, plant more corms in two-week intervals until late June. Gladiolus have bulbous root structures called corms that need to be planted in 5- to 6-inch holes.  I always put some fertile, OMRI Listed Black Gold Natural & Organic Garden Soil and bulb fertilizer in the bottom of the hole to ensure good growth. Plant corms in rows 6 to 8 inches apart in a cutting garden or more closely in small groups of 5 to 9 corms mixed in with tall, bushy perennials to provide upright patches of bright color. Water evenly. Gladiolus do not like wet feet or parched soil conditions.

Glads are one of the most long-lasting cut flowers for bouquets, which is why commercial florists love them. They can last for a week or two in a vase. Pick them when the stems just start blooming and remove the lower leaves. Cut the stems diagonally with sharp shears, and put them in water fortified with cut-flower food. A tablespoon of fully sugared lemon-lime soda to a quart of water also works.

Some gladiolus are hardy but most are tender. Gently dig the corms of tender types up in fall when their leaves turn yellow.  You will find new, small cormlets attached to the main corm. Keep them all to grow new plants, though the cormlets will take a full second season to reach flowering size. Put the corms in a warm, dry place for 2 weeks until they are dry. For storage, hang them in mesh bags in a cool, dry place through winter.

Gladiolus to Grow in Gardens

Unsupported tall glads tend to fall over, which is why caging or staking is recommended.

There are several types of gladiolus for gardeners to grow.

Standard sword lily (Gladiolus hybrids, Zones 8-10) range in height from 3 to 6 feet tall and may have up to thirty 5- to 6-inch flowers on each stem. There are hundreds of exciting varieties. A festive choice is ‘Frizzled Coral Lace‘ with lacy coral-pink flowers that fit the name. The rose and peach ‘Guinea‘ is a very pretty extra tall one, and the breathtaking ‘Zizanie’ has large blooms in broken shards of red and white. When planting taller glads like these, choose a location with low wind and surround the plants with perennial or tomato cages to keep them upright. Staking also helps. Planting corms an inch deeper may also assist with stabilizing the plants.

Hooded sword lily (Gladiolus primulinus hybrids (syn. G. dalenii), Zones 8-10) are shorter (2-4 feet) and have an unusual floral shape, with the top petal of the flower hanging over the rest.  They have large blooms, often with ruffled edges, that come in lots of color variations. An extra pretty one is ‘Las Vegas‘ with its primrose-yellow flowers edged in scarlet. The bright red ‘Mirella‘ is another choice selection.

Dwarf sword lily (Gladiolus nanus hybrids, Zones 7-10) reach only 1.5 feet tall. They have large flowers in many colors, including lots of bicolors.  Some of the blooms are white with a rose teardrop on every petal.  Dwarf glads are hardier, so more gardeners can grow them as perennials. Try the super-compact varieties in the Glamini® Series. They are less hardy (Zones 8-10) but perfect for containers or summer borders.

Exceptional Gladiolus species are offered by some bulb companies. One of the best is the hardy Byzantine sword lily (Gladiolus communis subsp. byzantinus, Zones 6-10) with its upright swords of smaller, pink flowers. It is an heirloom that makes a fine addition to old-fashioned perennial gardens. Another to try is the large-flowered branched sword lily (Gladiolus ramosus, Zones 8-10). The brilliant pink, purple, and red ‘Vulcano‘ is spectacular! The hardiest of them all is the butterfly sword lily (Gladiolus papilio, Zones 3-6). Try the bold, deepest-red ‘Ruby‘ with its striking, butterfly-like blooms on 30-inch stems.

More Gladiolus Notes

Hooded gladioli have top petals that create a hood over the bloom.

About leaving corms in the ground, I have some standard red hybrid sword lilies that I did not get around to digging up last fall in my USDA Hardiness Zone 6 garden.  Imagine my surprise when they came up hale and hearty this spring.  I was really surprised! I have read that planting them in 7- to 8-inch holes will increase the chance of them coming back ni northern gardens. Some mulch over the top also helps.

Two excellent companies I recommend for buying glads are Brent and Becky’s Bulbs, and K. van Bourgondien. Glads are blooming bountifully now, but their corms are only sold in the spring, so look for them in March to have the pick of the best varieties. Gladiolus are some of the most gorgeous flowers in the summer garden, so plan to plant some in yours.

How Can I Keep Plants Cool During Scorching Heatwaves?

Move potted plants to cooler locations during the most dangerous periods of a heatwave.

“It has been hotter than it’s ever been on record. How can I protect my plants from the severe heat?” Angie of Walla Walla, Washington

Answer: It’s scary when you live in an area that typically has mild summer temperatures, and you unexpectedly experience super high heat. Your tender plants are as used to it as you are, which means they’re going to struggle. From what I have read, your average June temperatures have highs around 80 degrees F. Being faced with temperatures well over 100 and even 110 degrees F must be really awful. Here are some ways to help protect your plants, especially those that are less heat tolerant. Specimens planted in full sunlight during the hottest times of the day (around 2:00 pm to 4:00 pm) need the most protection.

Four Ways to Cool Plants in High Heat

  1. Irrigate plants very well in the early morning. If temperatures exceed 100 degrees F, water again in the evening after the sun has fallen.
  2. Protect plants that are in full sunlight with floating row covers fitted with white shade cloth. These covers are easily placed over plants and removed. You can also simply purchase shade cloth and drape it over highly exposed plants. Both methods help. Gardeners in your area have also informed me that they have been moving patio umbrellas around their yards to shade their most prized plants. (One even said that her neighbor did not, and it resulted in some substantially fried rhododendrons and hostas.)
  3. Move containers into shaded areas or indoors during the most dangerous heat and water twice daily.
  4. Opt for lightweight, light-colored mulches. A cooling layer of straw around vegetable roots will really protect plants from heat, and long-fibered sphagnum peat moss makes a good, cooling cover for shade beds and containers. (Click here to learn about more mulch options.)

I also want to note that pets and wildlife also feel the stress. Leave water out for the animals and keep your pets from going outdoors for extended periods of time and walking on hot surfaces (grass only!). I also recommend that you read the following two garden articles for more helpful tips.

Cool Gardens: Designing for Summer Temperature Control

Nine Water-Saving Garden Tips to Fight Drought

Stay cool and happy gardening,

Jessie Keith

Black Gold Horticulturist

What Small Trees Can I Plant Close to My Home?

“Is there a type of ornamental tree that I can plant within 6 feet of my house (in zone 5)?” Amy of Grand Rapids, Michigan

Answer: Aside from being attractive and suited to your garden and area, any tree that you choose must be compact and have a root system that is somewhat shallow. Here are five selections that are both beautiful, compact, and native.

  1. Lavender Twist® Weeping Redbud (Cercis canadensis ‘Covey’): This small tree reaches between 8-12 feet when fully mature, but its weeping crown maintains a tidy, compact appearance. Redbuds are native to eastern North America and have beautiful spring flowers of purplish-red. Grow this one in full sun and well-drained fertile soil.
  2. Spring Glory® Serviceberry (Amelanchier canadensis ‘Sprizam’): White spring blooms, edible summer fruits that attract birds, and orange-red fall leaves make this an outstanding 12-foot small tree for home gardens. Grow this one in full to partial sun. 
  3. Golden Shadows® Pagoda Dogwood (Cornus alternifolia ‘Wstackman’): The gold and green foliage of this 10- to 12-foot variegated dogwood will light up any partially shaded location around the home. 
  4. Fringe Tree (Chionanthus virginicus): Loads of delicate, fringed, fragrant ivory flowers in spring make this small tree an excellent specimen to plant near a home. Mature specimens may reach 12 to 20 feet, so this is on the larger end of what you can plant close to the home. Full to partial sun is preferred.
  5. Blue Arrow Juniper (Juniperus scopulorum ‘Blue Arrow’): Here’s an evergreen option that hails from Colorado. It has tidy blue-green foliage and a narrow, upright habit. Trees reach just 12 feet at maturity. Full sun is required.

[Click here for an excellent guide on how to plant and site trees and shrubs.]

I hope that this helps!

Happy gardening,

Jessie Keith

Black Gold Horticulturist

Do Old Coffee Grounds And Tea Leaves Help Gardens?

 

“Are sprinkling used coffee grounds around flowerbeds or tree and shrubs a good idea?  We have our neighbor dogs and cats issues. Thanks!” Misty from South Carolina

Answer: It’s a question that I asked myself some time ago because my grandmother’s favorite amendments for roses were old tea leaves and coffee grounds. Both organic materials, derived from plant leaves and seeds, are slightly acidic and break down quickly, so essentially they act as quick compost at a slightly low pH suitable for roses. Coffee grounds also contain needed plant macro and micronutrients, such as phosphorus, potassium, and magnesium, while tea leaves contain a decent level of nitrogen, a macro-nutrient that encourages leaf growth.

Extra organic matter is always beneficial and encourages beneficial microbes as well, so placing grounds and leaves around other plants that appreciate slightly acid soil would also be a good idea, especially if you work them into the soil. Following up with proven soil amendments designed to make your garden plants thrive, like Black Gold Garden Compost Blend and Earthworm Castings, is also highly recommended.

Happy gardening,

Jessie Keith

Black Gold Horticulturist