Eight seasonal horticulture stories
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Editor's note: The spring 2020 Garden Packet, prepared by University of Illinois Extension horticulture educators, contains eight gardening stories. Photos are available.

What can we do to help support pollinators?
 Bees are one of the most well-known pollinators, but many other insects and some birds and mammals are also pollinators.
 Bees are one of the most well-known pollinators, but many other insects and some birds and mammals are also pollinators.

URBANA, Ill. – Pollinators have been in the news a lot the last few years due to their population declines. About 75% of all plant species are pollinated by animals and 90% of flowering plants, so pollinators are important parts of our ecosystems, says Ken Johnson, University of Illinois Extension horticulture educator.

“While we tend to focus on bees, particularly honeybees, other insects such as butterflies, moths, flies, beetles, wasps as well as some birds and bats will also pollinate plants,” Johnson says. “Without pollinators, our world would look a lot different.”

When we talk about the importance of pollinators, we tend to focus on their role in our food supply. About a third of the food and beverages we consume depend on pollinators.

“Pollinators’ impact on agriculture is worth around $29 billion in the U.S. alone and between $235 billion and $577 billion worldwide,” Johnson says.

Apples, broccoli, carrots, cucumbers, herbs, peaches, raspberries, and watermelons not to mention chocolate and coffee need animals to pollinate them. “Without pollinators, our grocery stores would look much different,” Johnson adds.

Pollinators are also important in nature. “Pollinators are a keystone species, or a species on which other species of the ecosystem depend,” Johnson explains. “The plants they pollinate are food for other animals – birds, mammals, and insects – and the pollinators themselves are also food sources. Without pollinators, there would be far less plant and animal diversity in our natural areas.”

Pollinator populations are declining. A variety of factors contribute to the decline: habitat loss, pests and diseases, climate change, invasive species, and misuse and overuse of pesticides.

Johnson offers a few tips on homeowners and gardeners can do to help support pollinators:

  • Get rid of some of your lawn. Lawns don’t have a lot to offer pollinators. Remove some of your lawn and plant it with flowers.
  • Choose heavy pollen and nectar-producing plants. Pollinators feed on pollen and nectar, so the more you can provide the better.
  • Plant a variety of flower, for multiple season blooming and blossom shapes. Different pollinators are attracted to different types of flowers and different pollinators are active at different times of the year. However, avoid heavily modified flowers such as double blooms.
  • Plant in clumps rather than single plants. Groupings of plants are more attractive to pollinators than solitary plants.
  • Be more accepting of weeds. Many of the weeds we try to eliminate from our landscapes can be good sources of pollen and nectar for pollinators.
  • Provide habitat for nesting and egg laying. Provide layers in the landscape such as trees, shrubs, tall grasses, low growing plants as well as bare patches of ground.
  • Allow for an untidy garden and accept some plant damage. Don’t be in a hurry to clean up the garden in the fall and spring. Many bees nest above ground in cavities such as hollow flower stems, while dead tree trunks provide habitat for wood-nesting bees and beetles. Allow some plant damage: beetles will often eat flower petals; leafcutter bees cut up leaves; and caterpillars will eat foliage. Getting rid of caterpillars gets rid of moths and butterflies.
  • Rethink the use of pesticides. Follow Integrated Pest Management practices by using pesticides only when necessary and don’t apply to plants that are in bloom.

For more information on pollinators and ways you can support them check out Illinois Extension’s pollinator fact sheets.

News source/writer: Ken Johnson, Horticulture Educator, Illinois Extension
Date: May 4, 2020

Use native prairie plants in the home landscape
 Prairie dropseed is a warm-season native grass that is great for landscaping as it will tolerate a wide range of soils, including clay.
 Prairie dropseed is a warm-season native grass that is great for landscaping as it will tolerate a wide range of soils, including clay.

URBANA, Ill. – Illinois is known as the “Prairie State” and has several native prairie plants. These plants are good options to include in the landscape because they evolved with the climate, soils, and pathogens in this habitat for thousands of years. 

Native prairie plant species have advantages:

  • Extensive root systems make prairie plants resistant to drought and dry conditions
  • Native prairie plants can reduce soil erosion.
  • Prairie plants have few insect and disease problems.
  • Once they’re established, prairie plants need minimum maintenance.
  • Prairie plants provide habitat for birds and other grassland animals.
  • Several native plants, such as milkweed,s are necessary for native insects.
  • Using native plants can cut down on exotic invaders to gardens.

Prairie plants are best planted in the spring. Late fall is the best time to sow prairie plant seeds directly.  You can purchase native plant species from reputable local nurseries or catalogs. Usually, plants from a local source are adapted to your area. Avoid digging native plants from the wild.

While there are many noteworthy prairie plants, some favorites include prairie dropseed, little bluestem and purple prairie clover.

Prairie dropseed (Sporobolus heterolepsis), also called northern dropseed, is a clump-forming, warm-season native grass. The graceful arching leaves give the plant a fountain-like appearance. Prairie dropseed is a very good native grass for the landscape as it will tolerate a wide range of soils, including clay.  Full height of the plant in flower is 2 to 3 feet and spread is 2 to 3 feet across. In late summer, open-airy flower heads appear on thin stems which rise above the clump of foliage. Pink and brown-tinted flowers are borne in sparse clumps at the end of the stem. The foliage turns golden with orange hues in the fall, fading to light bronze in the winter. The plant gets its name from the tiny rounded seeds, which drop to the ground in autumn when mature.

Little bluestem (Schizachyrium scoparium) has bluish stems that change from orange to russet red color throughout the fall and winter. Little bluestem’s common name refers to the bluish coloration at the base of the stem.  It reaches a height of 2 to 4 feet and has a dense root system which may reach 5 to 8 feet deep. Fluffy white seed heads are produced in late summer on arching stems. 

Purple prairie clover (Dale purpurea) is a slender plant that grows up to 2-feet tall.  In June and July, purple thimble-like flowers are produced at the ends of the stems. 

The Illinois Department of Natural Resources publication Prairie Establishment and Landscaping by William E. McClain has a list of sources for native Illinois prairie plant seeds.

News source/writer: Jennifer Fishburn,  Horticulture Educator, Illinois Extension
Date: May 4, 2020

Increasing the life-span of your urban tree
 Mulch improperly applied in a muffin shape around base of tree.
 Mulch improperly applied in a muffin shape around base of tree.

URBANA, Ill. – Urban communities responded to an increasing lack of interaction with nature by planting trees. Trees provide environmental benefits, along with their beauty, such as cooling buildings through shade and cleaning the air and water through filtration.

“Many urban trees only live about 20% of their life due to external issues, such as pests and disease, said University of Illinois Extension horticulture educator Kelly Allsup, "but most stress can be linked back to improper care and installation.” 

A recent USDA paper analyzing tree life expectancy in urban areas found the typical street tree lived between 19 and 28 years. To compare, the ideal life span of a white oak is 600 years, and the average life span of a red maple can be between 75 to 150 years in the Illinois wilds.

Urban trees must withstand pollution, poor soils, limited legroom for roots, and pressure from insects and disease. What’s worse, most are planted incorrectly, and their health and cultural requirements – sunshine, water, soil, and climate – are not monitored, Allsup says.

Some basic knowledge of tree stresses can help your urban tree live longer.

Plant the right tree in the right place. It is essential that certain growing parameters be considered when choosing what kind of tree to plant. Allsup suggests, answering the following questions before choosing a tree: How much space does the tree require at maturity? What are the culture requirements of the tree? What is the soil like? What is the soil pH needed and soil type (well-drained or compact)? Does the site get full sun or partial sun? How much water does that tree need? What is the growth rate of the tree? What kinds of things does the tree tolerate (salt, drought, flooding)?  What are the insect and disease issues that tree faces? What are the planting needs and pruning needs of the tree?

Don't plant trees too deep. “Trees planted too deep look like a telephone pole and their natural root flare cannot be seen above the soil line,” she says. This leads to roots not getting enough oxygen and the potential for strangling roots. The proper planting hole should be two to three times as wide as the root ball and no deeper. Rough up the sides with your shovel so roots will spread easier. Sometimes, the tree is planted too deep in the container or root ball.  It is essential that you dig a little to find the top root and plant at that depth and only backfill with the existing soil. “Amending soil may have good results in the beginning but ultimately cause roots not to expand and may cause issues with watering,” Allsup says.   

The worst and best thing for a tree in an urban environment is pruning. Improper pruning practices, such as topped trees and stubbed branches, cause the tree to grow weak branches and create a potential avenue for insect and disease issues. Proper pruning allows good structural growth, protection from wind and reduces the risk of tree failure. The reason urban trees need to be pruned while forest trees do not is because urban trees grow massive side branches that would usually be shaded out in a forest environment. Learn the basics of tree pruning and start corrective pruning at the time of planting.

Use the proper mulching technique. Mulch should not contact the trunk of the tree.“In the industry, we say mulch like a bagel and not like a muffin,” Allsup says. Use organic mulch, such as hardwoods or cypress. Extend a 2- to 4-inch-deep mulch ring as far out as you are willing to go. Properly mulched trees will require less frequent irrigations, less competition with grassroots, and keep trees safe from lawn mower damage.

Reduce strangling or girdling roots. Girdling roots circle the base of a tree rather than spreading out. These roots cut off the sap flow from the stems and leaves and water and nutrient flow from the roots to the leaves and branches causing the tree to decline at a rapid rate, most likely within five to 20 years. Some tree species are naturally prone to girdling roots like maples, ashes, crabapples, lindens, pines and oaks.

Girdling roots are caused by planting trees too deep, the planting hole is not wide enough, sides of planting hole not roughed up, improper mulching, pot-bound circling roots at time of planting, obstructions like sidewalks and curbs and poor soils. Signs of girdling roots can be no trunk flare, leaning trunks, bark cracks, branch dieback, and leaf issues. Research has shown that a third to half of trees that fall after a storm can be attributed to girdling roots. It is much easier to prevent girdling roots rather than fix it when a tree starts showing signs of decline. If a tree is pot bound, cut off circling roots, make sure roots lay straight and follow good planting practices and monitor trees to avoid girdling roots in the future.

Space your trees properly for their mature size. Small trees that grow 10 to 30 feet tall typically need a 20-foot diameter. Medium-sized trees that grow 30 to 50 feet typically need a 30-foot diameter. Large trees that grow more than 50 feet typically need a 40-foot diameter.  Knowing the mature canopy spread will help you better determine the spacing of your tree. “Many homeowners make this mistake by planting a small sapling close to their house only to cut it down later or try to over prune not allowing the natural shape of the tree,” Allsup says. 

Do not use staking materials unless you must and remove them after one season. The only reason to use staking materials is if wind is an issue at the site or as protection from vandals. Staked trees have decreased trunk diameter, develop poor root systems and usually suffer from rubbing of materials when they are staked.

By following these steps, you can increase the life of your trees and help ensure it will outlive you and not the other way around.

News source/writer: Kelly Allsup, Horticulture Educator, Illinois Extension
May 4, 2020

Reviving your compost pile after winter
 Getting your compost pile going again after the long, cold winter can be intimidating, but it is possible with a little bit of time and careful management.
 Getting your compost pile going again after the long, cold winter can be intimidating, but it is possible with a little bit of time and careful management.

URBANA, Ill. – If you haven’t touched your compost bin or pile all winter, don’t worry, you are not alone! 

“Getting your compost pile going after the long, cold winter can be intimidating, but it is possible with a little bit of time and careful management,” says Gemini Bhalsod, University of Illinois Extension horticulture educator.

For a successful compost pile, assess your starting point, manage the inputs, then begin turning for a hot pile in no time. The first step is to check to see how your compost pile or bin is doing.

“Be sure to see if there have been any unintended additions over the winter, such as large branches or trash,” Bhalsod says. It is also important to check if any parts of your bin are broken, wood is cracked, or  plastic is broken. Make any necessary repairs.

Determine if any of the pile is still active or if it froze through. “Active compost piles produce heat,” Bhalsod says. “So you might see some finished compost at the bottom or middle of the pile, or you might notice some steam coming off the pile.”

If you notice either of these things, your compost is likely still cooking!

Turning the compost pile will require effort. Use a pitchfork to mix the materials and incorporate air into your pile. Composting is a recipe: the beneficial organisms that do the work, with the right combination of air, water, carbon, and nitrogen. "Your goal is to provide the perfect home for these organisms to do their work so you can get compost at the end of the process," Bhalsod says.

After the winter thaw, compost piles are likely to be wet and soggy. If wet, don’t add water, just turn it. If your pile is dry, consider adding water to get it moist.

Add brown and green carbon and nitrogen-source material to the pile. In general, add three-parts carbon material to one-part nitrogen. Bhalsod recommends adding three buckets of brown material to every bucket of greens you add. Some carbon sources include dry leaves, straw, pine needles, and sawdust. Nitrogen sources include fruit and vegetable kitchen scraps, grass clippings, and plant trimmings.

As you continue, monitor your pile. Water it when it is dry and turn it at least once a week. If you follow these steps, your compost pile should be working again in no time.

News source/writer: Gemini Bhalsod, Horticulture Educator, Illinois Extension
Date: May 4, 2020

Familiar tale: Victims of emerald ash borer and other exotic pests
 The emerald ash borer is an exotic insect that has infected and killed native ash trees throughout the Midwest.
 The emerald ash borer is an exotic insect that has infected and killed native ash trees throughout the Midwest.

URBANA, Ill. – The emerald ash borer (Agrilus planipennis) has plagued native ash trees in Illinois since 2006.  This pest was first introduced in 2002 around the Detroit area and rapidly spread across Michigan and Indiana to infect most of Illinois today.

"Sadly, the emerald ash borer will eventually wipe out our native ash species in Illinois as we know them, leaving a major void in our urban forests and natural areas since ash is currently so prevalent," says Ryan Pankau, a horticulture educator with University of Illinois Extension. “The age-old phrase 'history repeats itself' certainly holds true with exotic pests and diseases in North America."

Two such past incidences have caused the virtual elimination of American elm and American chestnut trees across our continent.

American Chestnut

The impact of chestnut blight was extensive. The American chestnut's native range spans more than 20 states in the eastern U.S., from Maine to Georgia, and accounted for about 50% of the eastern deciduous forest.

“Chestnut was a highly prized timber and wildlife tree, producing nuts for wildlife and even humans, as well as lumber of superior quality,” Pankau says. Chestnut wood has excellent resistance to rot with fiber as strong as many of the oak species we covet today.  It was used for everything from structural lumber to fine furniture.

“It is just really hard to imagine how the disappearance of chestnut impacted life in the eastern United States, changing everything from timber products to the diversity of biota in eastern forests,” Pankau says. 

Chestnut blight does differ from emerald ash borer because it is fungal pathogen of chestnut as opposed to an insect pest. The fungus was first identified in its native land of China where it was hardly a pathogen of any significant threat, typically infecting dying twigs and bark.

"However, since our native chestnuts don’t have any co-evolutionary history with this pathogen, they have little resistance," Pankau says. Once established, the pathogen spreads from tree to tree by wind dispersion, creating cankers that grow rapidly and girdle stems.  

Infected chestnut trees were first observed in New York City in 1904. By 1940, chestnuts were wiped out as a commercial species and active component of its original ecosystem. To this day, chestnut still exists in its home range because the roots and root collar are resistant, allowing sprouts from old root systems to grow before the pathogen attacks and kills the above-ground portion of the plant.

American Elm

“The fate of American elm was determined by a combination of fungal pathogen and elm bark beetles, collectively referred to as Dutch Elm Disease,” Pankau notes. “Very similar to the emerald ash borer, larvae of the elm bark beetle tunnel into the wood of elm trees.”

As the larvae feed on infected trees, they are exposed to fungal spores which they disperse after emerging as adults and feeding on other elm trees. Once introduced, the fungus grows into conductive tissues in the tree. As the tree’s defenses respond, the conductive tissue is clogged, stopping transport of water and nutrients, while the pathogen persists. 

“It is an interesting relationship between insect and fungi, that is somewhat limited by the dispersion rate of beetles, spreading slower than wind-dispersed pathogens like Chestnut Blight,” Pankau explains.

Dutch Elm Disease was introduced near Cleveland in the 1930s, reaching Chicago in the 1960s and the western limits of American elm’s natural range by the 1970s. Although American elm did not have the timber value of chestnut, it had a much more extensive range, extending from the east coast to the Dakotas and down to central Texas.  It was a large component of eastern forests, occupying a wide range of environmental conditions.

“This adaptability made the elm an excellent urban tree that was widely planted, creating a huge impact to urban forests as the disease spread, much like what we are seeing with emerald ash borer today,” Pankau says.

Emerald Ash Borer

Emerald ash borer is fatal to ash trees because the larvae eat the conductive tissue within branches and trunks, often causing death within two to five years of initial infection. The beetle does fly and disperse on its own, but human movement of firewood has rapidly advanced its spread. Ash trees are important timber species, as well as urban trees, comprising up to 50% of the urban forest in some cities. 

“As an arborist, it has been very sad to watch the spread of emerald ash borer as it follows in the footsteps of past introduced outbreaks,” Pankau says. “We need to carefully consider the tree species we choose to replace ash and focus on planting a wide variety of native species to create a diverse and resilient urban forest.”

Inevitably, history will repeat itself and the strength of our urban tree populations will lie in the diversity of species that comprise them.

If you are interested in planting replacements for infected ash trees or selecting a new tree species to plant on your property, it is important to include a diversity of species that are adapted to local conditions.  Illinois Extension’s “Selecting Trees for Your Home” website, go.illinois.edu/treeselection, can help you find the perfect tree to compliment your planting location and add to local tree diversity.

News source/writer: Ryan Pankau, Horticulture Educator, Illinois Extension
Date: May 4, 2020

Pick an All-America for your garden
 yellow cherry tomatoes growing on plant
 The Apple Yellow cherry tomato has a firm and meaty texture and a sweet citrus taste. Each plant has up to 1,000 fruits.

URBANA, Ill. – Thunderstorms, snow, and ice, oh my! To beat the winter blues, one may turn to the 2020 seed and plant catalogs for spring inspiration and warmth.

“Planning your garden is essential to make sure you have plants that can tolerate our cold temperatures and still have blossoms all year long,” says Bruce J. Black, University of Illinois horticulture educator. “After mapping out your existing perennials, think about what new plants could be added to your landscape. A great starting place is the All-America Selections.”

All-America Selections, AAS, is a non-profit organization that releases several trialed plants each year as AAS Winners. AAS tests new varieties every year at their 80 private and public trial sites located around the United States and Canada. Currently, there are five trial locations in Illinois: three northern, one central and one southern. Independent judges, who are professional horticulturists in geographically diverse areas, evaluate trial entries against comparison plants. The results and observations are compiled and winners are chosen. For the best plants suited to the area, Illinois residents should look for Great Lakes winners or national winners on the AAS Winners lists.

Fourteen 2020 AAS Winners have been announced. Six were mentioned in the previous article. The five additional are discussed below which include four vegetables and one flower. They include:

  • Pumpkin, Blue Prince F1 (Cucurbita maxima var. Blue Prince F1):  Blue flattened 7-9 pound pumpkins with orange flesh. Noted for its savory sweetness and scoring high in: early maturing, fruit size, uniformity, color, etc. 90 days to harvest from transplant. National Vegetable Winner.
  • Tomato, Apple Yellow F1 (Solanum lycopersicum var. Apple Yellow F1): Apple-shaped tomato with a firm and meaty texture. Sweet citrus taste with good eating quality. Indeterminate vines with up to 1,000 fruits per plant. 110 days to harvest from transplants. National Vegetable Winner.
  • Tomato, Chef’s Choice Bicolor F1 (Solanum lycopersicum var. Chef’s Choice Bicolor F1): Pink and yellow beefsteak, early maturing and uniformed variety. Producing up to 30+ fruits per plant. 75 days to harvest from transplants. Four disease tolerances noted. Regional (Heartland) Vegetable Winner.
  • Tomato, Galahad F1 (Solanum lycopersicum var. Galahad F1): High-yielding sturdy planted tomato with Late Blight resistance. Sweet and meaty flavored 12-ounce fruits. Compact and determinate. 75 days to harvest from transplants. Regional (Heartland) Vegetable Winner.
  • Coleus, Main Street Beale Street (Solenostemon scutellarioides var. Main Street Beale Street):  Main Street Beale Street is the first-ever coleus AAS winner. Deep red foliage that holds its color through the season. An upright, bushy plant that grows uniformly and flowers very late in the season. Full sun to full shade tolerance. National Winner.

Looking for something else to fill in your landscape and gardens? The All-America Selections website has a list of all past winners since 1933.

For more information about gardening, check out the University of Illinois Extension website Watch Your Garden Grow at web.extension.illinois.edu/veggies or the Illinois Extension Horticulture YouTube channel at go.illinois.edu/UniversityOfIllinoisExtensionHorticulture.

Photo Credit: All-America Selections encourages the use of these images of AAS Winners by the media and garden communicators. Please credit All-America Selections and use the variety name. Variety name: Solanum lycopersicum var. Apple Yellow F1

News source/writer: Bruce J. Black, Horticulture Educator, Illinois Extension
Date: May 4, 2020

Spring landscape cleanup
 Hands pruning dead foliage.
 Be careful when pruning not to damage new growth.

URBANA, Ill. – After the 2019 growing season, there is likely leftover landscape clean up needed besides the usual spring yard work.

“Early cold weather and rain shut down a lot of clean up last fall,” says Richard Hentschel, University of Illinois Extension horticulture educator. If the cold weather and rain were not enough, the unexpected very cold weather surprised many trees, leaving lots of foliage dead, but hanging on, to come down later. 

Leaf cleanup will be a combination of those leaves you intentionally left as mulch to protect tender perennials and newly fall-planted items and late falling leaves.  

“Do not uncover the perennials too early, exposing them to yet cold temperatures and the rabbits,” Hentschel says.

Winter snow loads and spring winds will contribute to the small branches and twigs on the lawn. If you have the chance, pick them up and add them to the outdoor fire pit so they do not interfere when raking the lawn.

Do not overdo that first effort to clean up the lawn. The idea is to get the initial debris off the lawn while not removing any of the tender green grass.  Remember, each grass plant has been pushed up from freezing and thawing and needs time to get those roots firmly back into the soil, Hentschel says. "Nothing mechanical here, just the leaf rake for now."

While waiting on the lawn to dry more, consider some necessary pruning in landscape beds. The warm-season perennial grasses left up for the winter should be pruned down before growth resumes. Use a bungee cord to pull the top growth together to make the cut back easier and not as messy as removing a few grass stalks at a time.

All the matted foliage from daylilies and hosta can be cleaned. "Be gentle with hosta," Hentschel says. "The new buds for this year are going to be just underneath in the center, so use your hands rather than a rake."

While the flowering shrubs are still dormant in the home landscape, pruning out any dead and winter-damaged branches is going to be easier too. “Dead and damaged branches are easy to spot,” Hentschel says. “Color is a giveaway.”

Dead and damaged branches are always going to be a different color than the rest of the healthy branches in the canopy. Other shrubs needing attention are landscape roses that have been damaged over the winter. Prune away damaged canes until you see good green color. It is okay to gently reshape the whole landscape rose so new growth comes out evenly.

“While it might be tempting to do some digging in the dirt, it is better to wait on that until the soils are drier so soil structure is not destroyed and you just end up with lumps and clods of soil later,” Hentschel says.

News source/writer: Richard Hentschel, Horticulture Educator, Illinois Extension
Date: May 4, 2020

Starting seeds indoors
 Growing herbs from seed at home is easy and saves money.
 Growing herbs from seed at home is easy and saves money.

URBANA, Ill. – Herbs are a favorite in most gardens, but transplants can be expensive. As an economical alternative, University of Illinois Extension horticulture educator Nancy Kreith suggests starting seeds indoors in early spring as warmer weather approaches.

Herbs can be started in March and be ready for transplanting into the garden in May depending on your region of Illinois. Kreith recommends referring to the Illinois State Water Survey for your region’s average frost-free dates.

Thymerosemarybasilsagechives, and tarragon are great choices to start indoors. The seeds are very fine and take a fair amount of time to germinate. Oregano started by seed may not be true to the type of seed planted, and flavor will vary.

“Experts recommend propagating strong-flavored plants by root division or cuttings to ensure best flavor,” Kreith says.

To start herb seeds indoors, use a soil-less seed-starting mix that is peat or coir-based along with a 4-inch-deep container that provides drainage. Most brand name soil-less mixes work well for seed starting. Pre-moisten the mix with water until it reaches the consistency of a wrung-out sponge. Fill a container or seed-starting flat with the moist mix leaving about ¼ inch of space at the top.

Prepare the seeding area by sorting various seeds and labeling containers with the herb name and planting date.

Plant at least five seeds – or a pinch – of one herb variety per container or cell and lightly cover it with moist mix. “As a general rule of thumb, plant a seed two times its thickness under the soil,” Kreith suggests.

After planting, keep seeds moist during the germination period. “One technique is to cover the flat or container with a clear plastic bag,” Kreith says. The plastic helps hold in heat and aids in providing consistent moisture. “However, be sure to monitor the growing media for mold growth.”

If you see mold, make a hole or open a corner of the bag or remove it completely to improve air circulation. Supplemental moisture can also be provided by using a spray bottle. Additionally, the bag should be removed once the seeds germinate in 10 to 14 days. Use of a heat mat will speed the germination rate.

As plants become overgrown, seedlings can be thinned out to one plant per pot. Select the strongest and most compact seedlings.

The sown containers or flats need about six hours of sunlight per day.  A window with either a western or southern exposure will work well at the beginning, but over time the herb seedlings will require more direct and intense lighting. Using supplemental grow lights or florescent lighting has proven to work better than natural sunlight.

“If using fluorescent lights, keep them on for a minimum of 10 hours per day and place them as close to the seedlings as possible, adjusting height as seedlings grow taller,” Kreith says.

Monitor the seeds and seedlings daily as the transplants mature. Be on the lookout for insects, rot, and extremely dry soil.

The seeds and seedlings should only need a light sprinkle of water about twice per week, depending on the size of your pot along with temperature and humidity levels. A good practice is to allow the planting media to dry out a little before watering again. Overwatering can lead to diseases such as damping-off, a common soil-borne fungal disease that ultimately kills young seedlings. Constant moisture can also attract fungus gnats.

“As seedlings mature some maintenance will be needed,” Kreith says. If seedlings become overgrown, they can be transplanted into a larger cell or a bigger container. If they become leggy, they may not be getting enough light. “Be sure fluorescent lights are placed close enough to the plants, no more than 4 inches away,” Kreith says. “Lights can also be increased to up to 16 hours per day.”

Once seedlings reach six to eight weeks old, pinch back the top leaves to help the plants become bushier. Most herb seedlings should be ready to transplant outdoors in about 10 weeks.

“Help plants ‘harden off,’ or become acclimated to outside conditions by placing them outdoors on mild days and bringing them back inside every night. Keep plants out direct sunlight initially and continue the process for five to seven days,” Kreith recommends.

Once plants are hardened off they can be transplanted safely into the garden.

While transplanting the seedlings, you may also sow some seeds directly in the ground. Herbs that do well by direct sowing include cilantroarugula, and basil. Direct-seeding cilantro and arugula, both cool-weather herbs, in early spring provides a bountiful leafy harvest from mid-spring to mid-summer. Warm-loving herbs like basil can also be directly sown after the danger of frost has passed.

For best flavor, harvest herbs just before they flower. Visit University of Illinois Extension's herb gardening page to learn more details about specific herbs, their growing requirements, and harvesting and storing methods.

News source/writer: Nancy Kreith, Horticulture Educator, Illinois Extension
Date: May 4, 2020

Through agriculture and natural resources programs, Illinois Extension supports the economic viability and environmental sustainability of natural and managed landscapes and productive lands in Illinois. Horticulture program educators provide research-based information and training about gardening, fruits and vegetables, flowers, insects and diseases, composting, landscaping, and more.


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