Hort Notes 2026 Vol. 37:3

A monthly e-newsletter from UMass Extension for landscapers, arborists, and other Green Industry professionals, including monthly tips for home gardeners.

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Announcements

Pollinator Steward Certification Program: Summer Cohort

Registration for UMass Extension's Pollinator Steward Certification program summer cohort is now open through May 31 or until full. 

This fully online, asynchronous, self-paced course provides essential foundations in pollinator ecology and habitat provisioning.

Learn More & Register

UMass Labs Updates

Soil Lab in the News 

Check out the WCVB Channel 5 segment on how to collect a soil sample.

Plant Diagnostic Lab Achieves Significant Accreditation

Early this year, the UMass Extension Plant Diagnostic Lab achieved Core Accreditation from the National Plant Diagnostic Network (NPDN), one of just ten land-grant university-run labs across the United States to attain the designation.

The accreditation recognizes the lab’s commitment to high standards of diagnostic accuracy, scientific rigor, and quality assurance, and affirms its ability to provide reliable, research-based diagnoses and management recommendations that support land care professionals and agricultural producers across Massachusetts and beyond.

Visit the lab on the web for a list of services, sample submission instructions, and contact information.

Hot Topic

Spring Plants for Pollinators

The first blooms in Massachusetts each spring offer more than just a welcome sign of spring’s arrival: native pollinators depend on the early-season pollen resources to survive. While temperatures still fluctuate greatly in April and early May, dozens of bee species take the first opportunity to provision their offspring.

These early spring fliers include a group of bees who forage pollen exclusively from willows (Salix spp.). All seven willow specialist bees in Massachusetts belong to the genus Andrena, also known as mining bees. Females emerge in April, concurrent with the bloom of the floral hosts they depend on. As each female visits willow trees, she packs pollen onto her hind legs to transport back to the nest she’s excavated underground. These solitary bees don’t have the cooperation of a hive, so it is the job of each female to build, protect, and forage for her offspring. The success of her offspring depends on her ability to source adequate quantities of willow pollen for them to feed on in their larval stage.

Many bee species consume virtually all of their protein in the larval stage, which supports the development of adult structures like antennae and wings as they pupate. Specialist bees develop solely on the pollen of their floral host. Beyond willows, there are many other plant families which act as floral hosts for bee species in New England. Dogwoods (Swida spp.) are another spring-blooming resource for four documented mining bee species in Massachusetts, alongside the plant family Ericaceae.

It’s not just specialists that rely on pollen in April and early May. New queen bumblebees emerge alongside some of our solitary specialists, foraging on available resource-rich plants to build their fat stores after a long and cold winter. She uses this energy not only to activate her ovaries, but also to fuel nest-searching flights. Bumblebees often nest in abandoned rodent holes underground, but their preferences can vary among species and locations. Once a queen lays her first brood of workers, she remains in the colony for the rest of her life and allows her daughters to do the foraging for her.

Willows, dogwoods, and herbaceous perennials, like wood betony, provide so-called “shoulder season” support for pollinators. While summer hosts the peak in insect abundance and visibility in the landscape, spring and fall are critical for the reproductive success and ultimate survival of many species. This spring, keep your eyes and ears open for bees buzzing on May blooms!

Nicole Bell, Pollinator Specialist, UMass Extension 

Trouble Maker of the Month

Yellow Pot Mushrooms

Small, spongy, yellow mushrooms are sometimes observed growing in bags of potting soil or in potted plants. These mushrooms are most often Leucocoprinus birnbaumii (Lepiota lutea), commonly known as the yellow pot mushroom or yellow parasol. In the U.K. they are called “plant pot dapperlings.” They usually pop up in moist, warm potting medium that is high in organic matter. They may also appear in warm, wet weather on lawns or in garden beds, often in the vicinity of old tree stumps. This fungus is harmless to plants and feeds only on decaying organic matter.

Yellow pot mushrooms may appear singly or in clusters. They have bright yellow caps when young, but fade to white as they mature. Caps are textured on top, and the gills on the underside are free (i.e. unattached at the stem). There is a ring around the stipe (stalk) below the cap. The caps produce abundant white spores, which may be visualized by leaving the cap overnight on a dark surface.

Despite the fact that they look just like mushroom-shaped Peeps^TM candy, yellow pot mushrooms are inedible. Although it is generally held that ingestion may only cause “mild gastrointestinal distress,” their exact level of toxicity is unknown, and they should not be eaten.

If these mushrooms are a concern in the home or garden, they may simply be removed (no need to wear gloves) and discarded off site or in the trash. Potted plants may be placed outdoors or in areas inaccessible to small children and pets.

To discourage yellow pot mushrooms, avoid overwatering. Potting medium may be replaced. Wash pots thoroughly and disinfect with a 10% bleach solution prior to reusing. Outdoors, increase air circulation and sun exposure to decrease relative humidity. These mushrooms are typically not a persistent issue, but once the fungus is established it may be difficult to eradicate.

Angie Madeiras, Extension Educator & Diagnostician, UMass Extension Plant Diagnostic Lab

Q&A 

*Have a question for our experts? Email them to extlandscape[at]umass[dot]edu (extlandscape[at]umass[dot]edu) with the title Hort Notes Q&A. We will feature reader questions in future issues!

Q. I noticed that my distributor is selling the product Arkon. Is this a different option than Vexis?

A. Arkon and Vexis have the same active ingredient, pyrimisulfan. Pyrimisulfan is an ALS inhibitor, and controls weeds by preventing the synthesis of the acetolactate synthase (ALS) enzyme, which is critical for the biosynthesis of branched-chain amino acids (leucine, isoleucine, and valine). Halosulfuron (SedgeHammer^TM and ProSedge^TM) have the same herbicide mode of action.

Vexis is a 0.025% granular, formulation of pyrimisulfan that is packaged in a 2-pound shaker container and a 15-pound bag that is meant to refill the shaker container as it is used.

Arkon is a 0.103 pound per gallon, liquid formulation of pyrimisulfan. In 2025, Arkon was introduced by PBI Gordon as another formulation of pyrimisulfan. As a liquid formulation, its rates are aligned better with other herbicide products, both preemergence and postemergence, labelled for and commonly used in turf. This makes the target rate easier to achieve compared to the granular, shaker formulation of Vexis. Arkon as a sprayable formulation provides better control of yellow nutsedge and kyllinga.

Q. I happen to be very allergic to poison ivy. What is the best way to prevent having a “less than great time” when working around poison ivy? 

A. In the April 2026 (Vole 37:2) edition of Hort Notes, extensive information was provided about poison ivy characteristics and best management practices.

Q. I have heard that Miscanthus sinensis is now on the invasive plant list in Massachusetts. Is this correct?

A. Yes, that is correct. Miscanthus sinensis, (Chinese silver grass, eulalia, or maiden grass) is now considered to be invasive in Massachusetts. On December 8, 2025, the import and propagation of this species became prohibited in Massachusetts, and all sales will become prohibited on December 31, 2026. Information on deadlines for importation, propagation, and sale of Miscanthus sinensis and other recently listed species can be found at the Massachusetts Department of Agricultural Resources’ Massachusetts Massachusetts Prohibited Plant List.

Randall Prostak, Weed Specialist, UMass Extension 

Garden Clippings: Tips of the Month

May is the month to . . . 

• Deadhead the flowers of spring bulbs but leave the foliage in place until it starts to turn yellow. The leaves continue to produce and store nutrients that are essential for next year’s bulb and flower growth. It is also a good time to work a balanced fertilizer, such as 5-10-5, into the soil. Each plant should receive a teaspoon to help build energy for next year’s blooms.
• Plant roses in areas that receive at least 6-8 hours of direct sunlight each day. Miniature varieties are suited for rock gardens or for growing in containers on patios, decks, or front steps.
• Avoid applying insecticides to fruit trees, as they bloom, to be mindful of pollinating insects.
• Plant grape vines in well-drained soil, spacing plants about 8 feet apart against a trellis. When selecting grapevines, choose one year old plants. After planting, prune each vine back so only two buds remain to favor root growth over fruiting.
• Install stakes for some perennials and young trees. Stake tall perennials early while they are small. Only stake newly planted trees if they are top heavy or exposed to strong winds to encourage thicker trunks and more extensive root systems.
• Mow the lawn as growth dictates but aim to remove no more than 1/3 of the total shoot height with each mowing (the Rule of Thirds). Maintain a height of at least 3 inches to improve rooting and drought resistance.
• Work well-decomposed compost into flower and vegetable beds. It improves soil quality and helps the soil hold moisture through the summer heat.
• Stay on top of spring weeding to nip nuisance plants in the bud before they become a problem later in the season. Lay carboard or mulch paper in beds, between plants, to discourage weeds.
• Consider green mulches, like leaf litter, to promote pollinator nesting habitat. Thick layers of wood chips, for example, can obstruct soil nest entrances and exits for pollinators.
• Maintain clean water in bird baths. Dirty water in birdbaths can harbor mosquito larvae, so refreshing them regularly is prudent. Attract birds to the garden with bird feeders (while taking note of bear activity and relevant local guidance, however!); in turn they will also eat many unwanted insects.
• Purchase flower and vegetable starts from greenhouses. Inspect plants thoroughly and do not purchase plants that are showing signs or symptoms of insect or disease problems. Avoid plants with yellowing or mottled leaves or that are growing in overly wet or dry soil. 

Lina Ye and Harmonie O'Loughlin, Commercial Horticulture, UMass Extension  

Growing in High Organic Matter Soils

Sometimes it is necessary to construct soil for landscaping. Raised beds, new developments, and contaminated sites all often require new topsoil to support healthy plant growth. With proper construction and management these soils can be highly productive, but material availability often means that constructed soils are higher in organic matter than the natural soils of Massachusetts. These soils need to be treated a little differently from natural soils.

Before focusing on managing constructed soils, it’s important to talk about how soil should be constructed. Constructed soils should be made to mimic natural mineral soil and amended with moderate amounts of compost. The best practice is to use natural topsoil that was removed for construction, but this isn’t always possible. By dry weight, most mineral soil in Massachusetts is at least 90% minerals with only - at most - 10% organic matter. Because organic matter is much lighter than mineral particles, this weight ratio translates to about 25% organic matter by volume. Thus, if natural topsoil is unavailable or too expensive, new topsoil can be constructed by mixing 2” of compost into the top 6” of subsoil. Newly constructed soils are often slow to settle in. During this time, it’s important to pay close attention to the soil chemical characteristics like pH and nutrients to get good plant growth while the soil develops.

Unfortunately, landscapers are often brought in after soil construction, and soil is often constructed based on material availability rather than long-term plant productivity. Issues like low fertility, low pH, or low organic matter can be corrected using soil amendments. However, when soil is built with too much organic matter it is often not practical or economically feasible to change the soil profile. This is more common in urban areas when municipal compost is available at much lower cost than topsoil.

When soil has a lot of organic matter (more than 20% by dry weight), it may start to behave like muck soil. Muck soils occur naturally in wetlands and are significant across the Great Lakes region of the US and Canada but are uncommon in New England. This has led to some complication when looking at routine soil tests in New England since the nutrient recommendations used across New England were developed using natural mineral soils rather than organic soils. Sometimes this has resulted in disappointing plant performance. With this in mind, soil scientists across the Northeast are currently working to develop regional nutrient recommendations for high organic matter soils. While regional recommendations are developed and validated, there are lessons from the management of organic soils in the Great Lakes which appear relevant to high organic matter soil management in constructed soils.

For organic soils (greater than 20% organic matter by dry weight):

1) Keep pH around 5.5 for organic soil. This applies when you would maintain pH around 6.5 for plants which do best in slightly acidic soils. While this may seem surprising, nutrient availability functions differently in organic soil and phosphorus, manganese, boron, and zinc can become unavailable at 6.5 in organic soils.

2) Make sure not to include mulch in soil samples. Do not include surface mulch, like wood mulch or straw, in a soil sample. This can overestimate the organic matter content and bias the nutrient profile because the mulch layer isn’t as biologically active as soil organic matter.

3) Assess nutrient availability using off-season routine soil testing and in-season saturated media extract testing to guide sidedress and foliar fertilization. Routine soil tests are meant to approximate full season nutrient availability in mineral soils. Unfortunately, they can overestimate nutrient availability in high organic matter soils. Saturated media extract (SME) tests show nutrients currently dissolved in the soil and should be used to adjust in-season fertility management. See paired routine soil, SME, and tissue tests showing differences in nutrient results below.

4) Pay attention to micronutrients (esp. Mn). Micronutrient deficiencies are rarely seen in mineral soils in Massachusetts, but this may not be the case with high organic matter soils. Routine soil tests can overestimate manganese (Mn) availability in high organic matter soils, and in some cases saturated media and tissue tests show low Mn despite good levels on the soil test (see below). Foliar feeding may be useful if a Mn deficiency exists in a high organic matter soil.

Routine Soil Test

Saturated Media Extract

Plant Tissue Test

Some useful resources for thinking about the high organic matter issue are:

• Soil for Raised Beds from Rutgers covers the best practices for constructing soils at small scales.
• The Guide to Vegetable Production in Ontario has a lot of information about working with organic soils. While it’s only focused on vegetables, it’s a useful resource for getting a sense of how organic soils function.

Artie Siller, Soil Health Educator, UMass Extension and Sam Glaze-Corcoran, Soil and Plant Nutrient Testing Lab Manager, UMass Extension

Additional Resources

• Sign up for our newsletters!
• For detailed reports on growing conditions and pest activity – Check out the Landscape Message
• For professional turf managers - Check out our Turf Management Updates
• For commercial growers of greenhouse crops and flowers - Check out the New England Greenhouse Update website
• For pollinator interests - Check out the Pollinator Buzz and follow us on Instagram.
• For home gardeners and garden retailers - Check out our home lawn and garden resources
• TickTalk webinars - Recordings of past webinars in this series are available. 

Diagnostic Services

• Landscape and Turf Problem Diagnostics - The UMass Plant Diagnostic Lab is accepting plant disease, insect pest and invasive plant/weed samples. By mail is preferred, but clients who would like to hand-deliver samples may do so by leaving them in the bin marked "Diagnostic Lab Samples" near the back door of French Hall. The lab serves commercial landscape contractors, turf managers, arborists, nurseries and other green industry professionals. It provides woody plant and turf disease analysis, woody plant and turf insect identification, turfgrass identification, weed identification, and provides a report that includes pest management strategies that are research based, economically sound and environmentally appropriate for the situation. Accurate diagnosis for a turf or landscape problem can often eliminate or reduce the need for pesticide use. See our website for instructions for sample submission, submission forms, and payment options.
• Soil and Plant Nutrient Testing - The lab is accepting orders for Routine Soil Analysis (including optional Organic Matter, Soluble Salts, and Nitrate testing), Particle Size Analysis, Pre-Sidedress Nitrate (PSNT), Total Sorbed Metals, Total Carbon, Total Nitrogen, and Soilless Media. The lab is also accepting samples for Plant Tissue analysis, including macro and micronutrients, total carbon, and total nitrogen. Testing services are available to all. The lab provides test results and recommendations that lead to the wise and economical use of soils and soil amendments. Visit the UMass Soil and Plant Nutrient Testing Laboratory website for updates and order forms.
• Tick Testing - The UMass Center for Agriculture, Food, and the Environment provides a list of potential tick identification and testing options.