Growing Petunias Indoors: Tips for Getting Petunias to Thrive As Houseplants

In the spring, many of us buy those tried-and-true annuals that provide floral interest all summer long.

Think geraniums, violets, marigolds, and of course, petunias. A trip to the nursery in the spring would not be complete without a hanging basket or three full of bright flowers.

When we take those hanging baskets down and throw their contents into the trash or compost bin, we know for sure that winter is coming.

What many gardeners don’t realize is that petunias are technically perennials. They’re just extremely tender, and can’t handle even the slightest suggestion of frost.

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People who live in USDA Hardiness Zones 9 and below have to dig them up when the first frost hits the garden to keep them alive.

However, you don’t have to throw away these perfectly good plants! If you keep them alive over the winter, you’ll have even bigger, stronger plants in the summer after.

If you’ve never overwintered an “annual” flower like this before, don’t feel overwhelmed. We’ll walk you through the whole process. Here’s what you can expect coming up:

A lot of people love petunias, but what they don’t know is that you can keep them from one year to the next so they bloom and do well again. Let’s figure out how!.

A Bit About Petunias

Petunias (Petunia spp. These are very common South American plants that you can find in most nurseries and home supply stores in North America.

From biggest to smallest, they are grouped into grandiflora, multiflora, and milliflora. They also come in a huge range of colors and patterns, like black, polka dot, and more.

They can have an upright growth habit, or they may be vining or spreading types. We delve more into the different types of petunias here.

There are hybrids and cultivars that do better in pots than others. Some grow big enough to fill out a garden bed, though.

They need lots of sun, well-draining soil, and moderate amounts of water. And, as we’ve mentioned, they can’t survive in cold weather. A hard freeze will kill them.

But if you live somewhere colder and still want to try growing them as perennials, you have a few options.

Propagation Is Also Worth a Shot

Before we jump in to tackle the topic of winter care in more detail, I’ll level with you:

Petunias aren’t the best plants for overwintering.

They’re shocked by the move indoors, and they will likely drop their leaves. We’re talking a real plant bloodbath with lots of foliar carnage.

In this case, it is important to keep the roots alive during the winter so the plant can come back to life, grow new leaves, and bloom again the following year.

If you love a petunia and want to make sure it makes it through the winter, you should definitely take a cutting, or maybe a few.

Cuttings are a great way to spread these plants, and you’ll be less likely to lose an important plant this way.

Cut off a stem that is at least six inches long and take off the leaves from the bottom half to make a cutting. Put the cutting in a seed-starting medium in a well-draining container.

It needs to be in a window that gets at least six hours of sun every day. The soil should be damp but not wet.

After spending the winter inside, you can plant it in the garden again in the spring. It will grow roots.

But you can also give winterizing the entire parent plant a go as well. Let’s take a look at the available methods.

You have two options when it comes to winterizing a petunia plant.

The first way is to put the plant somewhere out of the way of frost, like in a garage, and let it sleep. The second way is to keep the petunia alive inside in a sunny spot as a houseplant.

Remember that most petunias are annuals that only live for about three years.

This is the easiest way to keep petunias alive. There are some plants that do well as houseplants inside, like geraniums and fuchsias. But petunias can be hard to grow inside.

Part of the reason for this is that these plants naturally stop growing when the days get shorter, but you’re making them grow indoors against their will.

When you know a freeze is coming or when the temperature regularly drops below 40°F, you should go outside and cut back your petunias. The plant shouldn’t have any more flowers, and the stems should be cut back at least a third.

If your petunia isn’t already in a pot, you should dig it up and remove all the soil from around the roots by shaking or washing it.

Examine the plant closely for any signs of disease or pests. Pests often hide or leave plants when they are disturbed, so you might not see them. Instead, look for droppings, eggs, or webs.

You should not bring these pests or diseases into your home, where they could infect other plants you have stored there.

Transplant into a container that will accommodate the root ball. It should be filled with fresh potting soil and have good drainage.

Now, you want to ease your plant into dormancy.

Place it in the sunniest spot inside that you can provide. The plant does best in full sun, but if you need to, you can add grow lights to help the natural light reach the plant.

In order to get your plants to experience the same length of daylight as they do outside, slowly decrease the amount of light they are receiving.

At first, you also want to water as you normally would. It’s best to water less each week so that a half-inch more of the soil feels dry between times.

In other words, for the first week, the soil should feel consistently moist. The next week, the top half-inch should be allowed to dry out. The following week, the top inch of soil should feel dry before you water again, and so on.

All of the leaves of the plant will fall off within about a month or two. The plant is still alive, even though it doesn’t look good. It has just gone dormant, putting its energy into its roots instead of its leaves or flowers.

After that, stop watering, get rid of any leaves that are still on the pot, and put it somewhere dark, like your garage or basement.

You don’t want it to be too hot or too cold for your petunia; the best temperature is between 40°F and 50°F.

Now, it’s time to let your plant rest. You don’t need to water or care for your plants any differently during dormancy. Just make sure they have the right temperature and low light where they are temporarily living.

About six weeks before the last expected frost date in your area, do the opposite by slowly adding more water and moving the pot indoors to a spot that gets more sunlight.

In the same way that you slowly turned down the light to match the decreasing daylight outside, you want to expose the plant to progressively more daylight each day.

In other words, you need to put it somewhere that it will get some indirect light and one or two hours of direct sunlight (or extra light). Gradually increase this over a few weeks until it can sit in full daylight.

If it’s not going to freeze, harden off the petunia for a week after the last average frost date of the year. Only then should you put it back outside full-time.

By this time, the plant should have new foliage and should start growing again.

For hardening off, you need to leave the plant outside for an hour in a safe place with indirect sunlight and then bring it inside. The next day, give it an extra hour outside.

Every day after the third, add another hour. Keep doing this until it can handle a full day in the sun. Then it’s ready to go back to the great outdoors.

From now on, you can water, fertilize, and give the plant sunlight just like you would any other petunia.

You can put it in the ground or repot it into a larger container. We were able to put the plant in a small pot while it was dormant, but it will need more space to grow now that it’s awake.

There are lots of great tips in our growing petunias guide that will help you make sure your plant is happy in the garden.

The nice thing about this method is that you get to go on enjoying your petunias year-round. But the challenge is that your plant is going to want to go dormant. Petunias need a lot of sun to grow actively.

Bring your plant inside as described in the section above, but don’t prune it. Just remove any blossoms and dead leaves.

Place the pot in a window that gets a lot of sun and add a grow light to help the plants get extra light during the winter when the days are shorter.

For your petunia to stay alive, it needs at least 10 hours of light a day. If it doesn’t get that much in the winter, you’ll need to use the grow light for some of the day.

Keep the soil moist, with a texture that feels like a well wrung-out sponge.

Fertilize every six weeks with an all-purpose product suitable for container-grown plants.

This should keep your petunia growing all winter, though it probably won’t have any flowers. If it does lose its leaves, though, treat it like it has gone dormant, as we talked about above.

Once the spring arrives, you can harden the plant off and put it back outside.

✅ How to Grow Petunias from Seed – Start to Finish.