Geranium macrorrhizum, or big root geranium, is one of my all-time favorite perennials for its ease of cultivation, attractive foliage, pretty summer blooms, and incredible vigor. It’s perfect at the front of a perennial or shrub bed, along a pathway, or as a groundcover under shrubs. Big root geranium spreads and forms a dense carpet of foliage, but it’s not so aggressive that it becomes invasive. In this article you’ll learn all about planting, growing, and caring for this stunning plant.

Get to know Geranium macrorrhizum

Also called big root cranesbill, Geranium macrorrhizum is a perennial plant hardy in USDA zones 3 to 8. In my garden it’s a botanical wonder, tolerant of sun or shade, and flowering from late spring through early summer. The pretty magenta pink flowers are held 4 to 6 inches above the foliage and typically repeat on and off through the summer months. The plants grow a foot tall and offer garden interest from early spring though late fall. In fact the leaves turn an attractive deep burgundy-red in autumn. They’re also fragrant when rubbed or crushed with a pleasing minty scent. It’s this fragrance that helps make big root geranium both deer and rabbit resistant.

Geranium macrorrhizum spreads via thick rhizomes, horizontal underground stems, and forms dense clumps in the garden. It’s my go-to weed resistant ground cover and is also perfect for covering an awkward slope.

Where to grow Geranium macrorrhizum

This perennial is popular in cottage gardens, perennial borders, and as solution for challenging spots like slopes and dry shade. It’s not very fussy about its growing conditions and thrives in average garden soil with low to medium moisture levels. Well-drained soil is important but that doesn’t mean it has to be super dry. It just means that water should drain away after a rain because overly damp spots may cause root rot. Geranium macrorrhizum is considered to be drought tolerant and only needs to be watered after planting when the roots are becoming established. 

As for light, it’s tolerant of shade to full sun. In cool summer areas aim for full sun. In warmer regions, shade to part shade works best. Big root geranium flowers best in part to full sun. 

How to plant Geranium macrorrhizum

This perennial geranium is typically sold in 4 inch, 6 inch, or one gallon pots, but, if you’re lucky, you’ll have a friend with a plant that is ready to be divided and shared. However you source your plants, it’s a good idea to plant them as soon as possible. Before planting make sure the plants are well watered to help them adjust to being transplanted. 

When you’re ready, slip the plant carefully from the pot. If it’s very root bound, loosen the roots with your fingers. Dig the planting hole with a trowel and place the geranium, making sure it’s at the same level it growing was in the pot. Don’t bury it too deeply or too shallow as it may fail to thrive.

Caring for big root geranium

Love low care plants? You’ll adore big root cranesbill as it’s a hands-off perennial. Once established it doesn’t need much in the way of maintenance. Summer care for most types of perennial geraniums includes a shearing back after the bloom. With Geranium macrorrhizum there’s no need to grab your pruning shears because the foliage stays low and tidy so you don’t have to cut the plant back. I do clip off the spent flowers with garden snips as they fade as this extends the flowering period. 

The only other task I do is sprinkle an organic flowering plant fertilizer on the soil surface in spring when the foliage starts to emerge. This provides essential plant nutrients and helps ensure healthy vigorous growth.

Types of big root geranium to grow

Besides the species, there are a couple of options for gardeners. Here are two of my favorites:

• Bevan’s Variety – This is the most widely available cultivar of big root geranium and is a fast-growing perennial with bright green leaves and purple-pink blooms. With its spreading rhizomes, it forms a dense mat of foliage. 
• Biokova – This naturally occurring cross between Geranium dalmaticum and Geranium macrorrhizum is a stunning garden plant that is a smart choice for tough garden situations. ‘Biokova’ was named the 2015 Perennial Plant of the Year from the Perennial Plant Association and boasts low spreading foliage and charming white blooms.

When and how to divide Geranium macrorrhizum

Perennial geraniums are easily propagated through division and this can be done in early to late spring or in autumn. Dividing overcrowded plants gives the plants more space to grow and helps them spread into good-sized clumps. I divide my Geranium macrorrhizum plants every 3 to 4 years. It’s easy to do and gives me plenty of divisions to replant in my garden or share with friends and family. 

Here are the 3 steps to dividing this perennial:

• Step 1 – Using a shovel, dig up the plant or a portion of the plant. Lay it on a piece of cardboard or a tarp to keep the area tidy.
• Step 2 – Using a garden knife or trowel, separate the rootball into smaller pieces. Each section should have a healthy portion of roots and clump of leaves. 
• Step 3 – Plant the divisions in a new spot or pot them up to share. Water well after planting. 

Troubleshooting big root geranium

One of the reasons I love growing Bigroot geranium is that it’s virtually trouble-free. There are few insects that munch the leaves, it’s deer and rabbit-resistant, and the leaves are generally unbothered by plant diseases. The ones to watch for include leaf spot and rust. Dividing the plants every few years so they’re not overcrowded goes a long way to helping reduce issues. 

In very hot and dry weather the leaves may turn red early. If you notice the plant looking stressed, deep water to ensure it has the moisture it needs. 

4 ways to use Geranium macrorrhizum

This hardy plant is truly a workhorse in the garden. Here are some of the best ways to use it in the landscape.

1. Ground covers – As noted above, this is a vigorous, but not aggressive ground-covering plant. It’s a tough-as-nails option for areas you don’t want to mow and the flowers attract bees and other pollinators.
2. Edgings – Whether you’re looking for an edging plant for the front of a garden or along a pathway, big root geranium is up to the job. It forms tidy clumps of foliage and flowers with the interest continuing well into autumn. 
3. Under tall trees – Layering plants in the garden creates a lush landscape and Geranium microrrhizum is a top choice for planting beneath tall trees and shrubs. It even works when planted at the base of hedges. Keep in mind that the plants flower better when given a few hours of light each day. 
4. Slopes – A slope can be a challenge to mow and many gardeners opt to cover a slope with mulch and a few shrubs. That can work, but often weeds settle in and it becomes a lot of work to maintain. My preferred plant for a slope is a dense cover of big root geranium. The plants spread well, crowding out weeds, and offer an attractive solution for slopes. 

For more ideas on great ground covers, be sure to check out these articles:

• Planting a succulent ground cover in the garden
• Evergreen ground cover plants: 20 excellent choices
• The best ground covering plants for shade