ASHS Certified Horticulturist (CH) Examination — Questions and Answers

Question 1: What is the correct location to make a pruning cut when removing a branch from a tree?

Several inches beyond the collar
Flush with the trunk
Just outside the branch collar (Correct answer)
At the branch union midpoint

Correct answer: Just outside the branch collar

Cuts made just outside the branch collar preserve the wound-compartmentalization tissue that the tree uses to seal the wound and prevent decay.

Question 2: Which of the following is a fast-growing tree with compound leaves and invasive potential in many regions?

Tree of Heaven (Ailanthus altissima) (Correct answer)
Sugar Maple (Acer saccharum)
Tree of Heaven (Ailanthus altissima)
Northern Red Oak (Quercus rubra)

Correct answer: Tree of Heaven (Ailanthus altissima)

The Tree of Heaven (Ailanthus altissima) is an extremely fast-growing deciduous tree with large, pinnately compound leaves. It is notorious for its invasive potential in many regions, rapidly colonizing disturbed areas and outcompeting native vegetation. Its aggressive growth and prolific seed production make it a significant ecological threat.

Question 3: Slow-release fertilizers benefit landscape plants primarily because they:

Lower soil pH rapidly
Increase salt index immediately
Reduce leaching and provide sustained nutrition (Correct answer)
Eliminate the need for micronutrients

Correct answer: Reduce leaching and provide sustained nutrition

Slow-release fertilizers break down gradually, reducing nutrient leaching and providing a steady supply of nutrients over weeks or months.

Question 4: Which plant is characterized by its needle-like leaves and is commonly used in drought-tolerant landscaping?

Juniper (Juniperus spp.) (Correct answer)
Lavender (Lavandula spp.)
Blue Spruce (Picea pungens)
Rosemary (Salvia rosmarinus)

Correct answer: Juniper (Juniperus spp.)

Juniper (Juniperus spp.) is a genus of coniferous plants widely recognized for its distinctive needle-like or scale-like leaves. Many juniper species are highly drought-tolerant once established, making them excellent choices for xeriscaping and low-water landscapes. They are also valued for their evergreen foliage and diverse forms, from groundcovers to upright trees.

Question 5: Soil compaction during landscape installation is best prevented by:

Watering soil heavily before equipment use
Adding sand to clay soils
Rototilling compacted areas after installation
Restricting heavy equipment to designated access routes and protecting root zones (Correct answer)

Correct answer: Restricting heavy equipment to designated access routes and protecting root zones

Limiting equipment access to designated lanes and placing matting over root zones prevents compaction of soil pores, preserving aeration and drainage around plants.

Question 6: Which pruning cut removes a branch back to a lateral branch or bud, encouraging outward growth?

Heading cut
Pollarding cut
Deadheading cut
Thinning cut (Correct answer)

Correct answer: Thinning cut

A thinning cut removes a branch to its point of origin at a larger branch or trunk, maintaining natural form and redirecting growth without stimulating dense regrowth.

Question 7: When is the best time to seed cool-season grasses in the northern United States?

Early spring (March–April)
Midwinter (December–January)
Midsummer (June–July)
Late summer to early fall (August–September) (Correct answer)

Correct answer: Late summer to early fall (August–September)

Late summer to early fall provides optimal soil temperatures for cool-season grass germination and allows establishment before the onset of winter.

Question 8: Which practice BEST helps reduce turf compaction in high-traffic areas over time?

Combining core aeration with sand topdressing (Correct answer)
Increasing mowing frequency to keep grass short
Applying a pre-emergent herbicide to prevent weed competition
Reducing irrigation to limit root growth

Correct answer: Combining core aeration with sand topdressing

Core aeration physically removes soil plugs to immediately relieve compaction, and sand topdressing helps maintain open pores and improve long-term soil structure.

Question 9: Which perennial plant is known for its heart-shaped leaves and striking purple flowers?

Columbine (Aquilegia spp.)
Bleeding Heart (Dicentra spectabilis)
Hosta (Hosta spp.)
Violet (Viola spp.) (Correct answer)

Correct answer: Violet (Viola spp.)

Violets (Viola spp.) are well-known perennial plants characterized by their charming heart-shaped leaves and often fragrant, striking purple flowers. They are common in gardens and wild areas, typically blooming in spring. This combination of heart-shaped leaves and purple flowers is a defining characteristic of many violet species.

Question 10: Irrigation scheduling based on soil moisture sensors is preferred over calendar-based scheduling because it:

Is always less expensive to install
Works without any maintenance
Applies water only when plants actually need it, reducing overwatering (Correct answer)
Eliminates the need for a controller

Correct answer: Applies water only when plants actually need it, reducing overwatering

Soil moisture sensors measure actual water content in the root zone, allowing irrigation to trigger only when plants need water rather than on a fixed schedule regardless of conditions.

Question 11: In landscape design, the principle of 'unity' is achieved by:

Mixing all design styles in one space
Repeating compatible elements to create a cohesive, harmonious composition (Correct answer)
Maximizing color contrast throughout the landscape
Using as many different plant species as possible

Correct answer: Repeating compatible elements to create a cohesive, harmonious composition

Unity is created through repetition of plants, colors, textures, or forms that ties the design together into a visually coherent whole.

Question 12: Which of the following is considered a best management practice (BMP) for reducing stormwater runoff pollution?

Overwatering landscapes
Applying synthetic pesticides frequently
Installing rain gardens (Correct answer)
Using impervious pavement

Correct answer: Installing rain gardens

Installing rain gardens is considered a best management practice (BMP) for reducing stormwater runoff pollution. Rain gardens are specially designed depressions planted with native vegetation that collect and absorb stormwater from impervious surfaces. This allows water to infiltrate the soil, filtering out pollutants and reducing the volume and velocity of runoff that enters natural waterways.

Question 13: A landscape design element that provides a transition between tall trees and low ground covers is called a:

Understory layer or shrub layer (Correct answer)
Canopy element
Screen planting
Terminus

Correct answer: Understory layer or shrub layer

The understory or shrub layer bridges the visual and physical gap between tall overstory trees and low ground-level plantings, creating layered depth in a planting design.

Question 14: Which landscape feature is most effective for managing stormwater runoff on residential properties?

Expanded concrete driveways
Rain gardens (bioretention areas) (Correct answer)
Conventional turf with underground drainage
Raised decking over lawn

Correct answer: Rain gardens (bioretention areas)

Rain gardens are shallow, planted depressions that capture and infiltrate stormwater runoff, reducing peak flow, filtering pollutants, and recharging groundwater.

Question 15: What is the primary advantage of sodding over seeding when establishing a new lawn?

Sodding uses exclusively warm-season grasses while seeding uses cool-season types
Sod cannot be used on slopes greater than 3:1
Sodding provides instant, erosion-resistant coverage while seeding takes weeks to months to establish (Correct answer)
Seeding is always more expensive per square foot than sodding

Correct answer: Sodding provides instant, erosion-resistant coverage while seeding takes weeks to months to establish

Sodding provides immediate ground cover and erosion control, while seeding requires significantly more time for germination and establishment.

Question 16: A soil test reports low potassium. Which symptom would you most likely observe on affected plants?

Pale green color of entire plant
Purple discoloration of young leaves
Stunted root growth only
Brown scorching along leaf margins of older leaves (Correct answer)

Correct answer: Brown scorching along leaf margins of older leaves

Potassium deficiency typically causes marginal scorch (brown edges) on older, lower leaves because potassium is mobile and redistributed to younger tissue.

Question 17: Tissue culture (micropropagation) is preferred for propagating some plant species because it:

Produces large numbers of genetically uniform, disease-free plants rapidly (Correct answer)
Only works with seed propagation
Requires no sterile conditions
Is less expensive than cuttings

Correct answer: Produces large numbers of genetically uniform, disease-free plants rapidly

Tissue culture propagates thousands of identical, pathogen-free plantlets from tiny explants in sterile conditions, enabling rapid large-scale production of superior clones.

Question 18: Runners (stolons) are a natural vegetative propagation structure found in which common landscape plant?

Ornamental cabbages
Tulips
Hostas
Strawberries and many lawn grasses (Correct answer)

Correct answer: Strawberries and many lawn grasses

Strawberries and turfgrasses such as bermudagrass and St. Augustinegrass produce stolons — horizontal above-ground stems that root at nodes, naturally propagating the plant.

Question 19: What is a primary cultural practice to reduce the risk of root rot in plants?

Ensuring proper drainage in soil or containers (Correct answer)
Avoiding overhead irrigation
Planting in poorly drained soils
Watering heavily every day

Correct answer: Ensuring proper drainage in soil or containers

Root rot is a destructive plant disease caused by fungi or oomycetes that thrive in waterlogged, oxygen-deprived soil conditions. Ensuring proper drainage in soil or containers is crucial because it prevents excess water from accumulating around the roots. This allows roots to access necessary oxygen and reduces the anaerobic environment favored by root rot pathogens, thereby promoting healthy root development.

Question 20: Which soil amendment is best for increasing drainage in heavy clay soil?

Perlite (Correct answer)
Peat moss
Compost
Vermiculite

Correct answer: Perlite

Perlite is a lightweight, porous volcanic glass commonly used as a soil amendment to improve drainage and aeration, especially in heavy clay soils. Its irregular shape and porous structure create air pockets, preventing compaction and allowing water to move more freely through the soil. This helps mitigate the poor drainage issues often associated with clay.

Question 21: Over-irrigation of landscape plants most commonly leads to which root problem?

Salt burn
Nutrient toxicity
Excessive root hair growth
Anaerobic conditions promoting root rot pathogens (Correct answer)

Correct answer: Anaerobic conditions promoting root rot pathogens

Waterlogged soils become oxygen-depleted (anaerobic), promoting Phytophthora, Pythium, and other water mold pathogens that cause root rot.

Question 22: What mowing height is generally recommended for Kentucky bluegrass during summer stress periods?

2.5–3.5 inches (Correct answer)
1–1.5 inches
0.5–1 inch
4–5 inches

Correct answer: 2.5–3.5 inches

Kentucky bluegrass is typically maintained at 2.5–3.5 inches in summer to promote deeper roots and improve heat and drought stress tolerance.

Question 23: Which irrigation system delivers water directly to the root zone with the greatest water-use efficiency?

Flood irrigation
Overhead sprinkler
Sprinkler oscillation system
Drip/micro-irrigation (Correct answer)

Correct answer: Drip/micro-irrigation

Drip irrigation applies water slowly at or below the soil surface directly to the root zone, minimizing evaporation and runoff compared to overhead methods.

Question 24: Rain sensors on irrigation systems are required by law in some US states because they:

Detect pipe leaks
Automatically override irrigation during and after sufficient rainfall (Correct answer)
Improve water pressure regulation
Monitor controller battery levels

Correct answer: Automatically override irrigation during and after sufficient rainfall

Rain sensors interrupt irrigation cycles during or after adequate rainfall events, preventing wasteful over-irrigation and reducing stormwater runoff, which some states mandate.

Question 25: What is topdressing in turfgrass management?

Spreading a thin, uniform layer of material such as sand or compost over the turf surface (Correct answer)
Applying a post-emergent herbicide to the surface of the turf
Adding granular fertilizer on top of a straw mulch layer
Mowing at a higher height to cover thin or bare spots

Correct answer: Spreading a thin, uniform layer of material such as sand or compost over the turf surface

Topdressing involves spreading a thin, uniform layer of material (sand, compost, or soil mix) to improve surface smoothness, thatch decomposition, and soil physical properties.

Question 26: Pleaching is a tree-training technique that results in:

Trees grafted onto a single rootstock
Trees pruned into cloud shapes
Interwoven branches forming a hedge on stilts or overhead canopy (Correct answer)
Compact, low-growing forms through root pruning

Correct answer: Interwoven branches forming a hedge on stilts or overhead canopy

Pleaching weaves or ties together branches of adjacent trees to form a living fence, overhead canopy, or 'hedge on legs' for formal garden structures.

Question 27: Hardwood cuttings of deciduous shrubs are typically taken and propagated during which season?

Late fall to early winter during dormancy (Correct answer)
Early spring at bud swell
Mid-summer during active growth
Midsummer after bloom

Correct answer: Late fall to early winter during dormancy

Hardwood cuttings are made from fully lignified, dormant wood in late fall or winter, then stored or stuck in media where they slowly root during winter and spring.

Question 28: Air layering is a propagation method best suited for:

Producing seedlings under grow lights
Rooting a stem while still attached to the parent plant (Correct answer)
Propagating fine-rooted annual species
Separating bulb offsets

Correct answer: Rooting a stem while still attached to the parent plant

Air layering wounds a stem on the parent plant, packs the wound with moist sphagnum, and wraps it to encourage roots to form before the new plant is severed.

Question 29: The term 'plant caliper' refers to which tree measurement used in nursery specifications?

Tree height in feet
Crown spread in feet
Root ball diameter
Trunk diameter measured at 6 inches above ground (Correct answer)

Correct answer: Trunk diameter measured at 6 inches above ground

Caliper is the trunk diameter of a nursery tree measured at 6 inches above ground (or 12 inches for trees over 4-inch caliper), used as the standard sizing specification for shade trees.

Question 30: Which of the following is an example of an Integrated Pest Management (IPM) practice?

Eliminating all insects from the environment
Only using organic pesticides
Introducing natural predators to control pests (Correct answer)
Applying chemical pesticides preventively

Correct answer: Introducing natural predators to control pests

Integrated Pest Management (IPM) is a comprehensive approach to pest control that prioritizes long-term prevention and suppression with minimal environmental impact. Introducing natural predators, such as beneficial insects or microorganisms, is a key biological control strategy within IPM. This method targets pests without relying solely on chemical pesticides, aligning with IPM's goal of sustainable pest management.

ASHS Certified Horticulturist (CH) Examination

The ASHS Certified Horticulturist (CH) exam tests competency across seven horticultural domains including landscape design, plant production, propagation, pest management, and business practices. Administered by the American Society for Horticultural Science, it validates professional-level knowledge for practicing horticulturists.

Questions

35 min

Time Limit

70%

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