What is a Hardy Plant? A Complete Guide

Hardy plants are a gardener’s best friend. These plants are tough and can survive cold weather, bad weather, and poor soil conditions. But what exactly makes a plant hardy? This guide will explain what hardiness is, how to measure it, what makes plants hardy, and how to choose and care for hardy plants.

What is Plant Hardiness?

In simple terms plant hardiness refers to a plant’s ability to survive cold winter temperatures. The hardier a plant, the lower the temperatures it can withstand.

Hardiness is an important thing to think about when picking plants because it tells you which ones will do well in your area. The US Department of Agriculture (USDA) made a map of plant hardiness zones that shows how the country is split into areas with different average low winter temperatures.

This map serves as a guide to help gardeners understand which plants are most suitable for their zone. For example, if you live in zone 5 where temperatures can drop to -10 to -20°F, you’ll want to choose plants rated hardy to at least zone 5 or lower.

How is Plant Hardiness Measured?

There are a few different systems used to measure plant hardiness

• USDA Hardiness Zones: As mentioned above, this is the most commonly used system in the U.S. It divides the country into 13 zones based on average winter lows. Zone 1 is the coldest at -60°F and below, while zone 13 is the warmest at 60-70°F.

• Sunset Climate Zones: Popular in the western U.S., this system incorporates temperature, humidity, precipitation, and other factors. It uses a scale of 1-24.

• American Horticultural Society (AHS) Heat Zones: Ranging from 1-12, this measures heat tolerance and is used in conjunction with the USDA hardiness zones.

• Royal Horticultural Society (RHS) Ratings: Used in the UK, this system has ratings from H1a to H7, with H7 being the most cold hardy.

What Makes a Plant Hardy?

There are some amazing changes that plants have made that help them survive freezing temperatures. Here are some of the ways they achieve hardiness:

• Supercooling: Some plants can avoid freezing by lowering the temperature at which water inside their cells turns to ice.

• Extra Insulation: Certain plants grow thicker leaves, bark or cell walls to prevent freezing.

• Transferring Water: Plants can move water from cells into intercellular spaces, so it freezes there instead of inside the cells.

• Shedding Leaves: By dropping their leaves, some plants avoid damage from desiccation or wind chill.

• Going Dormant: Many hardy perennials die back to the ground in winter, surviving via hardy roots or crowns safely below the frost line.

Hardy plants also tend to have extensive root systems, thick cuticles to reduce water loss, and the ability to withstand drought, heat, wind, and poor soils. These tough constitutions allow them to thrive in challenging climates.

Tips for Choosing Hardy Plants

• Find out what zone your home is in and choose plants that are rated for that zone or at least one colder.

• Consider microclimates: Sheltered spots may allow you to stretch the zones. Avoid frost pockets.

• Select native plants: Plants native to your region are adapted to local conditions.

• Favor perennials: Hardy perennials are resilient and return each year.

• Look for indicators: Smaller leaves, fuzzy or waxy foliage and compact shape often indicate hardiness.

• Read labels carefully: Terms like “hardy,” “frost hardy,” or zone numbers offer clues.

• Research unknown plants: If needed, look up a plant’s native range and habitat.

Caring for Hardy Plants

While hardy plants are low maintenance, providing a bit of extra care will help them thrive:

• Water thoroughly: Give deep waterings during droughts so roots access moisture.

• Use mulch: A 2-3 inch organic mulch insulates plant roots from temperature extremes.

• Prune judiciously: Most pruning should be done in late winter to avoid cold damage.

• Provide wind barriers: Use fencing, shrubs or burlap to block desiccating winds.

• Improve drainage: Amend soil with compost to prevent waterlogging in winter.

• Allow self-seeding: Many hardy plants naturally self-seed for reliable returns each year.

Hardy plants form the backbone of low-maintenance, resilient gardens. Understanding exactly what hardiness means, how it varies by climate, and what adaptations plants use to survive will help you make informed choices. Consider each plant’s unique needs, provide winter protection where required, and your hardy plants will reward you with years of beauty and abundant returns.