Our collections feature over 21,000 plants and plant groupings.
And beyond their astounding beauty, they help to serve these important functions:
Biological diversity of the plant kingdom directly impacts all of Earth’s living things—especially humans’ quality of life.
Plant communities face challenges, like extinction and degradation, that can be addressed through research. Our findings are integral to the health of our ecosystem and the world at large.
The enjoyment of all
We take pride in connecting people with the wonder, beauty, and value of trees and plants. We display sustainable plants for northeast Ohio landscapes, and inspire action for healthy communities.
Our signature collections:
Our impact by the numbers
Total number of student and adult participants in onsite nature-based school lessons, offsite programming, adult classes and online learning across multiple departments (education, conservation and research) in 2020. Virtual classes reached participants in 9 states other than Ohio and 2 countries.
Horticulture & Collections
In our living collection (excluding our natural areas), the Holden Arboretum has 10,217 accessions* and the Cleveland Botanical Garden has 3,089 accessions.
* An accession is a particular type of plant received from a particular source at a given point in time in a particular manner (for example: seed, seedling, cutting, grafted plant, or tissue cultured plant).
Research & Conservation
Research staff published 17 peer reviewed papers during 2020 in journals such as Forest Pathology, Frontiers in Ecology and Evolution, and the American Journal of Botany, Diversity, and New Phytologist.
Trees and Plants FAQ
Let’s get to the root of our most commonly-asked questions.
Yes! Please provide images of the plant, including a close-up or two of leaves and flowers (or fruit if present), and let us know where it’s growing. We will get back to you—preferably via email, or by phone if necessary.
Perhaps, but diagnosing a plant malady can be tricky. Please include images and a description of the problem. If you’re stopping by the garden or the arboretum, you may leave a sample with a completed questionnaire.
The Ohio State University has many online resources that we refer to. We will answer via email or by phone.
You should smother it. We have used cardboard and mulch over the top, but old carpet or other materials can also be successful. Manually pulling, digging, and hoeing can help, but you may not be able to get it all in one or two years.
If you resort to herbicides, read and understand the label. Check the MSDS sheet online to get a better idea of what a particular herbicide’s hazards are. There’s no such thing as a “safe” pesticide operator without the proper information, protective equipment, and training.
Please use the scientific name if possible. We’re not aware of a list that compiles every garden center’s inventory in our region, but the Andersen Horticultural Library of the University of Minnesota has a helpful Plant Search Online.
If the plant you seek is a native or a wildflower, we may offer it at our Plant Sale. Check our website for dates and times as we only offer plants on occasion, and they go quickly. Lake County Soil and Water Conservation District also offers native trees in quantities of 5, 10, or 25 every year.
We appreciate your kindness, but we currently don’t take houseplants. On occasion, and with thorough consideration, we have accepted donated plants of collectors’ quality.
You may contact Rockefeller Park Greenhouse or the Miller Nature Preserve Conservatory of the Lorain County Metro Parks to see if they can use it.
After a storm, it’s important to evaluate and assess the damage, because every tree is different. The tree assessment will determine whether damage is superficial, treatable or beyond repair.
In some cases, the damage is so severe that after pruning and repairing the crown, the remaining tree might not survive or add much aesthetic value to the landscape.
Sometimes trees tip in storms, but are in otherwise good condition. If of a manageable size, they can be saved. First, the tree must be righted and supported with at least two wire cables tied to the trunk at about 2/3 of the height from the ground. These should be tied securely, but not too tightly, to prevent girdling. The wires should be placed to pull in the opposite direction of the tip or fall, and must be set at angles from each other.
If you have an uprooted tree, keep the roots moist and set it upright as soon as possible. If the roots dry out, the tree will die. After resetting the tree, fill in any gaps between the roots and surrounding soil with more soil. Finish by mulching to a maximum depth of 2 – 3”. It’ll need additional watering any week when less than one inch of rain falls.
For larger trees, consult an arborist for the best course of action. Tree work can be dangerous without the necessary knowledge and skills, potentially leading to damage or injury to life and property. Locate a certified arborist on the International Society of Arboriculture (ISA) website.
For many trees, shrubs, and even perennials, fall is a great time to plant—September into mid-October is ideal. Although many woody plants can be planted in the fall with excellent results, over the years nurserymen have observed that a few species often don’t thrive if planted in the fall.
These plants are more reliably planted in spring:
- Carpinus ssp. (hornbeams)
- Cupressus nootkatensis (Nootka cypress)
- Koelreuteria paniculata (golden raintree)
- Liriodendron tulipifera (tuliptree)
- Magnolia spp. (magnolias)
- Nyssa sylvatica (black gum)
- Populus spp. (poplars)
- Quercus spp. (oaks)
- Zelkova serrata (Japanese zelkova)
- Thuja plicata (giant arborvitae)
- Lilacs (Syringa) bloom early to mid-May. Many lilacs can be found throughout the Display Garden at Holden.
- Rhododendrons are for the most part spring bloomers but vary depending on variety. Below are some of our most prominent groups:
- Small-leaved rhododendrons bloom April to mid-May.
- Large-leaved rhododendrons bloom May to early June.
- Evergreen azaleas bloom late April to mid-May.
- Deciduous azaleas bloom throughout May and June and some into July.
- Many of our native wildflowers bloom from early April through mid-May.
- Flowering crabapples (Malus) bloom mid-April to mid-May. With crabapples, showy, floriferous blooms one year may be followed up by a less pronounced bloom the following year.
- Magnolias (Magnolia) bloom in April and May. Earlier blooming varieties are more susceptible to spring frosts. Some years, Magnolia varieties begin blooming as early as late March.
There are many factors that affect the timing and intensity of fall foliage and it varies from year to year, species to species, and even individual to individual. With that said, peak fall color at Holden Arboretum campus occurs mid- to late October. At the Cleveland Botanical Garden campus, peak color occurs late October to early November, although frost events can truncate the fall foliage later in the season.