How to Keep Your Mums Blooming Longer

You buy a mum covered in flowers, set it on the porch, and two weeks later it looks finished while the one on your neighbor’s step still looks good. Some of that is variety and how far along the plant was when it left the store. A lot of it is what happened after.

Extension sources put a well-cared-for mum at six to eight weeks of color. Most of the ones I see on porches get three. Here is what makes the difference, roughly in order of importance.

This is the big one. A finished mum is a very large plant sitting on a very small amount of soil. By the time it leaves the greenhouse the roots have filled the pot, and the canopy above them is pulling water out of that little root ball all day. On a warm, sunny afternoon in early fall a mum can need water twice in one day.

Do not wait for it to wilt. The plant itself will usually recover from a wilt, but the flowers do not. Open petals that have collapsed once do not come back crisp, and the buds that were about to open may abort. A mum that wilts a few times can burn through its display weeks early, which is exactly the three-week porch mum I described above. Check the soil every morning by pushing a finger an inch in. If it is dry, water until it runs out the bottom, and let the excess drain away rather than leaving the pot standing in it.

Get the hose or watering can under the canopy and onto the soil. Soaking the flowers every morning keeps the petals wet for hours, and that is what gray mold, the fungus Botrytis, is waiting for. It starts as small brown water-soaked spots on the outer petals and spreads inward until the whole flower is a brown mush. Oregon State’s plant disease handbook notes that the spores need a stretch of continuous wetness to infect, and that warm days followed by cool nights, which is every October day in Indiana, encourage condensation on the flowers. Rain is going to happen and you cannot help that. You can help by not adding overhead watering to it.

The most colorful plant on the bench is not the one that will give the longest show. It is the one with a lot of fat, developed buds and just enough open flowers to be sure of the color. You are buying this week’s flowers and next week’s flowers at the same time, and a plant that is fully open has already spent next week. This late in the season there may not be many tight-bud plants left, so look for the ones with the most unopened buds you can find.

Warm, sunny weather makes a mum drink faster and pushes the flowers through their cycle sooner. The mums that go out in early September during a hot stretch are the hardest to keep looking good. October conditions make the same plant much easier. Do not take that as a reason to put it in deep shade, because mums still need sun, ideally six hours or so. But if a long display is the goal, the hottest spot against the south wall of the house is not where it belongs.

While we are growing a mum we feed it hard, because we are building roots, branches and canopy over three months. By the time the buds set, that job is done, and we stop fertilizing a couple of weeks before the plants ship. Penn State’s care guide says the same thing for gardeners: discontinue fertilizing once the flower buds form. More fertilizer at this stage does not make more flowers or longer-lasting ones. If you feel you must, a half-strength dose of an all-purpose liquid feed once is plenty. Water management matters far more now than feeding.

Pull or snip off the flowers that have gone brown. This does not restart the plant, but it makes a surprising difference, because the fresh flowers underneath become visible and the plant stops looking tired. Penn State and NC State extension both note that regular deadheading helps prolong the flowering period.

Many mums get dropped, plastic pot and all, into a ceramic cachepot or a foil sleeve. Water collects in the bottom and the roots sit in it for days, which is the fastest way to rot a mum. Lift the inner pot out after watering and dump whatever is standing underneath, or poke holes in the foil.

The opposite problem is just as common. A peat-based root ball that has dried out completely becomes water-repellent. You pour water on top, it runs down the gap between the root ball and the pot, and the center stays bone dry while the saucer fills up. If a mum has gotten very dry, water it slowly, in two or three passes a few minutes apart, until the pot feels heavy. Virginia Tech’s extension guidance on container watering describes the same approach: add water slowly, let it soak, and repeat until the whole root zone is wet.

Heavy rain beats up open flowers. Wind dries the plant out faster. Heat raises water demand. And eventually a hard freeze will end the display. A mum in a pot has one advantage over everything else on the porch, which is that you can move it. On a night with a hard freeze in the forecast, or ahead of a storm that is going to pound the flowers, slide it into the garage or under the eave and bring it back out in the morning. Do not overdo it, though. Garden mums have real cold tolerance and shrug off a light frost. Covering or moving them only matters when the forecast is unusually severe.

• ✓ Buy it with buds remaining.
• ✓ Do not let it wilt.
• ✓ Water the soil instead of the flowers.
• ✓ Make sure the pot drains.
• ✓ Remove spent blooms.
• ✓ Do not overfeed it.
• ✓ Protect it from unusually severe weather when you can.

Do not treat a mum like a pumpkin just because they are both sitting on the porch in October. The mum is still a living plant in the middle of flowering, and it is working hard. Keep the roots consistently moist and the flowers reasonably dry, and you will get considerably more out of it before fall is over.

Reference: Penn State Extension, Chrysanthemum Care; NC State Extension, Caring for Mums Through the Fall; Pacific Northwest Plant Disease Handbook, Chrysanthemum Gray Mold; University of Kentucky Extension, Mums Make the Fall Garden Pop with Color; WVU Extension, Making the Most of Mums; University of Tennessee Extension, Containerized Fall Garden Mum Production; Virginia Tech Extension, Properly Watering Container Houseplants; Ball Seed, At-Risk Crops: Garden Mums; Schlegel Greenhouse production notes.