Maine Plant Hardiness Zones Map And Gardening Guide

Summary

Maine has many plant hardiness zones within its state lines, ranging from 3b to 7a. Its average minimum extreme temperatures range from -35°F (-37.2°C) to 5°F (-15°C). It has a cooler climate overall and is considered a humid continental climate. The state is split into three main growing regions: the north, the southern interior, and the coastal maritime climate. Each area experiences different types of weather based on wind direction and location relative to the coast.^1-5,7

Maine has a shorter growing season, ranging from 134 to 157 frost-free days per year. This state experiences cold, long winters, and if you are an avid gardener, a heated greenhouse is a good option to extend the growing season.^5-6

Maine experiences nor’easters and flooding brought on by its proximity to the Atlantic Ocean. In some areas like the southern interior, Maine has been experiencing a higher percentage of prolonged dry seasons, bringing on extreme drought and wildfires. It is said that the state, among many others, will continue to warm over the next decade.^6-9

In general, Maine’s soil conditions are on the acidic side, making it important to have a grasp on what plants do better in this type of soil and how to amend it to get a more neutral soil base.⁹

Plant suggestions include but are not limited to the following:^10-20

Shagbark Hickory
Rhododendron Rhodora
Red Columbine
Radish
Thyme
Basil
Blueberry
Sedum

Maine’s Plant Hardiness Zones

USDA Hardiness Zone	Average Minimum Extreme Winter Temperature Range Fahrenheit (°F) Celsius (°C)	Average Last Frost Date Range In Spring (Beginning Of The Growing Season)	Average First Frost Date Range In Autumn (End Of The Growing Season)
3b	-35°F to -30°F -37.2°C to -34.4°C	Mid to late May	Mid to late September
4a	-30°F to -25°F -34.4°C to -31.7°C	Mid to late May	Mid to late September
4b	-25°F to -20°F -31.7°C to -28.9°C	Mid to late May	Mid to late September
5a	-20°F to -15°F -28.9°C to -26.1°C	Early to mid-May	Late September to early October
5b	-15°F to -10°F -26.1°C to – 23.3°C	Early to mid-May	Late September to early October
6a	-10°F to -5°F -23.3°C to 20.6°C	Late April to early May	Early to mid-October
6b	-5°F to 0°F -20.6°C to 17.8°C	Late April to early May	Early to mid-October
7a	0°F to 5°F -17.8°C to -15°C	Late April to early May	Early to mid-October

Frost Date Sources: 1, 21-29

Maine’s Growing Conditions

General Climate^1-5,7

Map showing Koppen climate types in Maine. — Credit to Wikipedia

Maine has a humid continental climate and three climate zones: The northern portion, the southern interior, and the coastal climate. Each section experiences different types of weather based on wind direction and location relative to the coast.

The northern portion of the state is affected by wind coming from the west and north. This brings in cold, long winters with lots of snow. The summers are generally mild, and don’t often see extreme heat.

The southern interior experiences hot summers and is influenced by the south and west winds. As the climate warms, Maine experiences longer and longer dry seasons. This extreme weather has been causing forest fires in the state, seeing 900 in 2020.

The coastal region in Maine has a maritime climate. This portion of the state is affected by the Atlantic Ocean and moderates the extremes of the summers and winters in Maine.

The entire state of Maine experiences long, cold winters. The western and northern parts of the state see the most snowfall, receiving up to 100 inches of snow annually. The rest of the state sees between 40 and 80 inches of snow a year, depending on your proximity to the coast.

Microclimates

USDA plant hardiness zones are an important starting point for your garden, but you’ll also need to consider microclimates.

Microclimates are areas where specific conditions create a climate different from the climate they’re situated in.

Buildings, fences, paved areas, or short hills and valleys can create these microclimates.

They can be as small as a space in your backyard or as large as a city.

In other words, learn about your local conditions from local experts to see if your garden falls into a microclimate.

Extreme Weather^6-9

Extreme Drought

Due to the warming climate, Maine has been experiencing longer and more frequent periods of drought (most commonly in the southern Interior). Prolonged dry periods and extreme heat can negatively affect the garden if not prepared for. Watering will have to remain at a minimum, depending on the severity of the drought.

Xeriscaping is a water conservation method when designing a garden. This form of gardening includes smart watering techniques like mulching, adding organic matter to the soil, and more. This method also involves choosing hardy, drought-tolerant plants that can withstand the heat.

Nor’easters

Nor’easters are common in Maine from fall through into spring. They are defined as cold coastal storms that bring in lots of snow, sleet, and freezing rain. They can have tremendous winds and can cause flooding and major damage to your property and garden. They affect the coastal areas of Maine and can be really nasty!

Having a heated greenhouse is a splendid way to beat the cold, harsh winds of the Nor’easter storm fronts. A heated greenhouse provides growing opportunities all year round. These are especially good if you’re an avid grower.

Flooding

Climate warming affects Maine in more ways than heat. Due to its location within the higher mid-latitudes, the amount of annual precipitation from winter through spring is projected to increase in this state. The rate of extreme weather events is also said to increase, creating a risk of flash floods.

Flash floods cause runoff, which can bring pollutants into water sources. This can be detrimental to the health and quality of the water. Planting veggies, herbs, and flowers in raised wooden boxes can help with drainage and keep the plant roots dry.

Growing Season^5-6

Maine experiences long, cold winters, shortening the growing season, which lasts between 134 and 157 days a year. The season typically begins around April to May and ends anytime from September to October. Depending on your location, the growing season can be mild.

Plant cold-hardy veggies that don’t love too much heat for areas that deal with a prolonged winter. Examples include radish, lettuce, and kale. The southern interior should look towards heat-loving veggies during this short but hot growing season, with the anticipation for hotter, dryer summers. This includes plants like tomatoes, eggplant, and cucumbers.

Maine Gardening Tips^8-9

A white fence with colorful flowers all around it.

Do Off-Season Projects

Because Maine experiences long, cold winters, gardens are dormant for a large portion of the year. Just because the weather outside isn’t hands-in-the-dirt permitted, it doesn’t mean there aren’t valuable garden-related activities you can’t do this time of year.

Prepare your garden for spring by using the winter months to clean and sharpen tools, take inventory of your seeds, order more if needed, and plan and map out your growing area. By taking the necessary steps in the off-season, you can get a head start once the weather starts to warm.

Understand Acidic Soils

The majority of Maine’s soil profile is slightly on the acidic side. The soil type is called Spodosols and is typically found in the eastern Gulf states. This can affect growing as some plants don’t do well in higher acidity. Knowing what plants prefer this type of soil and the companion plants to help them thrive is an advantageous way to grow in Maine.

Some examples of plants that prefer more acidic soil and grow well together are blueberries, lilac, thyme, parsley, and basil. Rhododendrons and azaleas also prefer slightly acidic soils. For veggies, try radishes, sweet potatoes, and broccoli.

Consult With Local Professionals

Consulting with local gardening professionals allows you to benefit from their experience with your area’s conditions, the plants that do well there, and overall best practices.

Maine Plant Suggestions^10-20

Trees

Shagbark Hickory (Carya ovata)
Sassafras (Sassafras albidum)
Striped Maple (Acer pensylvamicum)

Shrubs

Northern Spicebush (Lindera benzoin)
Rhododendron Rhodora (Rhododendron canadense)
Arrowwood Viburnum ( Viburnum dentatum)

Flowers

Red columbine (Aquilegia canadensis)
Violet (Violaceae)
Blue Wood Aster (Symphyotrichum cordifolium)

Vegetables

Beauregard Sweet Potato (Ipomoea batatas)
Radish (Raphanus sativus)
Broccoli (Brassica oleracea var. italica)

Herbs

Thyme (Thymus vulgaris L.)
Sage (Salvia officinalis)
Lavender (Lavandula)

Spices

Wild Chervil (Cryptotaenia canadensis)
Parsley (Petroselinum crispum)
Basil (Ocimum basilicum)

Fruits

Blueberry Northern Highbush (Vaccinium corymbosum)
Beach Plum (Prunus maritimus)
Wild Strawberry (Fragaria virginiana)

Succulents

Eastern Prickly Pear (Opuntia humifusa)
Hens and Chicks (Sempervivum spp.)
Sedum (Sedum acre)

Disclaimer

Any of the above can change and is not exhaustive.

Treat anything above like a good starter guide. Then use that as a foundation as you consult with local gardeners, professionals, forecasts, guides, and organizations.

Sources

“Plant Hardiness”. US Department of Agriculture. Accessed March April 15, 2024.
Runkle, J., K.E. Kunkel. “Maine”. NOAA. 2022. Accessed April 18, 2024.
“Maine Planting Zones”. Gilmour. Accessed April 18, 2024.
“Humid continental climate”. Britannica. January 18, 2023. Accessed April 20, 2024.
Whitman, Andrew. “The three climate zones in Maine”. Research Gate. Accessed April 20, 2024.
“Maine-vegetable-planting-calendar”. Urban Farmer. Accessed April 17, 2024
“Drought Tolerant Landscaping”. Gilmour. Accessed April 18, 2024.
“Winterize Your Garden”. Gilmour. Accessed April 18, 2024.
“Growing and Harvesting in Maine”. Urban Farmer. Accessed April 17, 2024
“Native Plant Profiles”. Wild Seed Project. Accessed April 20, 2024.
“Vaccinium corymbosum”.Wikipedia. October 5, 2023. Accessed April 20, 2024.
“Petroselinum crispum“. Missouri Botanical Gardens. Accessed April 20, 2024.
“Basil”. Wikipedia. April 11, 2024. Accessed April 20, 2024.
Ferguson, Mary. “Pokey, Spikey Plants in Louisiana”. LSU College of Agriculture. November 30, 2023. Accessed April 16, 2024.
“Thyme”. Wikipedia. April 8, 2024. Accessed April 20, 2024.
“Sage, Salvia officinalis “. University of Wisconsin. Accessed April 20, 2024.
“Lavandula”.Wikipedia. April 1, 2024. Accessed April 20, 2024.
“Raphanus”. Wikipedia. October 26, 2023. Accessed April 20, 2024.
“PlantFinder”. Missouri Botanical Gardens. Accessed April 20, 2024.
“Succulents”. Pleasant Hill Property Service. Accessed April 20, 2024.
“Frost Dates for Caribou, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Presque Isle, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Bangor, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Greenville, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Augusta, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Lewiston, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Portland, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Brunswick, ME”. Almanac. Accessed April 21, 2024.
“Frost Dates for Eastport, ME”. Almanac. Accessed April 21, 2024.