What to Do With Hardy Geraniums in September – For Healthy Plants and to Keep Them Under Control
Avoid heavily cutting back hardy geraniums this month
Cranesbills or hardy geraniums (not to be mistaken with pelargoniums) have a long blooming period, often lasting into fall until the first frost. In September, they start to slow down, are past their peak display, and begin preparing for fall and winter – but, they do need a little help.
If you have hardy geraniums in your yard, you'll know they can spread fast and bloom profusely, but they're fairly low-maintenance. Come September, it's important to give them a bit of a tidy up. You should remove any damaged and diseased plant matter (with something like these sharp Fiskars bypass pruning shears from Amazon), divide overcrowded plants, and adjust your watering regime according to the seasonal shift.
As a hardy perennial (USDA zones 4-8), fall care is all about prepping these cottage garden staples for winter so they make a reliable return next spring. Here, with the help of garden pros, I talk through three key tasks to do this month.
1. Remove Disease and Damage
The first thing to do is tidy up your geraniums to remove anything damaged or diseased. This will strengthen these plants and ensure no diseases overwinter to re-emerge in spring and potentially spread elsewhere in your garden.
'You want to remove any brown or damaged leaves or any stems that have been damaged. If your geranium still looks healthy and it still has full color, then leave it alone. Cutting it back to encourage fresh growth is usually more useful right after its main flowering period than this late in the season,' says Lindsey Chastain, homesteader and founder at The Waddle and Cluck.
As Lindsey notes, heavy pruning should be avoided. It can encourage soft new growth that is vulnerable to frost damage, so it's best to stick to light pruning this month.
Hot and humid summer conditions can cause a few problems like bacterial leaf spot, powdery mildew. If you spot these, use essential pruning tools like the Felco F2 pruning shears from Lowe's to remove infected plant material.
'Diseased, decaying material needs to go, and when removed, that should not go in your compost because it will just transfer that to your compost. It needs to be bagged and trashed. Healthy foliage and stems just need to be left alone. Some hardy geraniums have a fall bloom, so you want to make sure that you're not doing a full clean-up of your area until they're done,' Lindsey advises.
Lindsey Chastain, a dedicated homesteader and skilled writer, is the driving force behind The Waddle and Cluck, a platform that celebrates sustainable living, gardening, and responsible farming
2. Divide Hardy Geraniums
With hardy geraniums growing so quickly (they're an excellent choice of fast-growing groundcover), they can become overcrowded in time. Every few years, it's a good idea to divide these plants to keep them productive. You'll also end up with new clumps to plant elsewhere in the garden.
'These plants respond well to division in fall (best divided every 3-5 years). Make sure each new division has healthy growth points and some roots, keep the root collar level with the ground, and prepare planting holes matching the root system size,' advises Plantum plant expert Marina Prokaten.
September (before hard fall frosts) is a good time to divide hardy geraniums, as you want the ground to be workable for lifting and replanting.
You can use a garden trowel (like this from Burpee) or a hori hori knife (like this from Amazon) to cleanly cut and separate the clumps.
Marina Prokaten is a resident plant expert for the Plantum app, which helps users identify plant species, diagnose their conditions, and get specific care advice. She has three years of experience consulting on botany-related topics for Plantum.
3. Water During Dry Spells
Hardy geraniums are considered fairly drought-tolerant once established and are susceptible to issues of root rot and oversaturated soil.
'In September, as temperatures drop and evaporation slows, reduce the watering schedule to prevent soggy soil and root rot before the plant enters winter dormancy,' Marina advises.
However, if there are any late-summer heatwaves or prolonged periods of drought in September, give your hardy geraniums a soaking.
Using a soil moisture meter (I like this one from Amazon), check the soil before watering if you're unsure. Ideally, you should allow the top 1-2 inches dry out before watering again.
What to Shop
Before frost, it can be a good idea to lightly mulch your hardy geraniums. There are plenty of fall mulching materials you can use, including fallen leaves, wood chips, and grass clippings. This will provide some insulation during particularly icy periods.
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