I love petunias and have grown them in pots, hanging baskets, and garden borders in two different climates (one with a mild Winter and one with a cold Winter).
Therefore, I have personally encountered many of the common problems with petunias that I talk about in this article, and I share with you the steps I took to save them. There’s even a mini experiment included in there!
I think the first thing we need to consider is that petunias are tender perennial flowering plants that do not tolerate frost or cold temperatures and die back in Winter.
Dying and wilting petunias are usually caused by fungal diseases such as root rot, which are caused by excess moisture around the roots. Petunias require thorough watering once a week and do not tolerate boggy soil from overwatering, which causes petunias’ leaves and flowers to wilt and results in dying petunias.
Yellow leaves are a symptom of root rot, not enough sun, or a lack of nutrients.
To prevent petunias from dying, we have to get the balance of watering and soil moisture right to avoid root rot or drought stress.
Keep reading to learn the best practices of care to prevent petunias from dying and how to revive your petunias so that they recover and display flowers…
Petunias Dying From Root Rot (Leaves Turning Yellow and Drooping)
The most common reason for dying petunias is because of the diseases root rot and Botrytis, which are caused by overwatering, slow-draining soils, and pots without drainage.
I find it is always helpful if we know where a plant comes from so that we can understand its preferred conditions and replicate those conditions to help it revive…
Petunias are native to South America where they thrive in full sun and moist, yet well-draining soil with good air circulation and low humidity.
If the soil around the roots of the petunia is too damp or even boggy, then this promotes the conditions for fungal diseases such as root rot and Botrytis which thrive in damp, slow draining soils that stay saturated for too long after watering or rainfall.
Even if the petunia does not have root rot, too much water around the roots excludes oxygen from the soil which is required for root respiration.
If the roots cannot breathe in the soil due to lack of oxygen, then this interferes with the roots ability to transport moisture and nutrients around the plant and causes the leaves of the petunia to turn yellow and die back.
The leaves also tend to look wilted and shrivelled as well as yellow due to root rot.
Your petunias thrive when the soil is watered generously, around once per week, which maintains the optimal balance of soil moisture without creating the damp conditions that cause root rot.
(Read my article, how to water petunias to learn how to establish the optimal watering schedule for petunias, according to your climate and conditions).
As you can imagine, petunias are relatively hardy to somewhat dryer conditions due to their South American origins and can even tolerate drought once they have established.
From my experience, I learned that the schedule of watering generously once per week and allowing the soil not to become too boggy emulates the typical watering cycle of the petunia’s native environment.
It is important to note that overwatering your petunias is not the only cause of excess moisture around the roots, causing the leaves to turn yellow:
- Pots and containers without drainage holes in the base. I have seen petunias planted in decorative pots that do not have drainage holes in the base, or the holes become blocked with compacted soil, preventing water from draining effectively.
- Trays underneath, pots or containers. Petunias grow exceptionally well in pots due to their favorable drainage conditions. However, another common problem I have seen is when trays are placed under the pot (to prevent water from spilling), which then collects the excess water after a bout of watering or rainfall and causes the boggy soil that causes root rot.
- Petunias dying in hanging baskets. Petunias are a favorite flower for hanging baskets due to their ability to resist drought-like conditions. However, I once saw a customer have a problem as the hanging basket was lined with plastic impermeable sheeting or other material, which can help retain moisture but, in this case, prevent water from escaping from the bottom of the basket. This caused the boggy soil to turn petunia leaves yellow and have a drooping appearance.
- Watering too often. If you water petunias every day, I can assure you that you are watering far too often. You need to scale back the watering to once a week and only increase the frequency during heat waves if the soil is drying out too quickly.
If your petunias have been in boggy soil for a long time and are suffering from a fungal disease, then it can be difficult to save.
However, your petunia may just be showing signs of stress if the excess moisture is preventing root respiration and it can recover if you ensure better drainage conditions and water less often.
My Steps for Reviving Petunias With Yellow Leaves…
- If your petunias are turning yellow in a hanging basket, I would check to see if there is a plastic membrane (and remove it) that may be preventing water from draining efficiently to help improve drainage, or you can just create some holes in the bottom like I do as I think this achieves a good balance of retaining some moisture (which is important in heat waves) and allowing the soil to drain properly.
- Ensure potted petunias are in pots with drainage holes in the base, and remove any compacted soil at the bottom of the pot. Ideally, you should re-pot the petunias with new potting soil and apply a 1-inch layer of gravel on the bottom of the pot to help ensure good drainage and prevent any blockages to the drainage holes.
- What I like to do is place your potted petunia on little feet or stands so that the pot is elevated an inch off the ground. If the pot is on the ground, then water may drain from the base of the pot, but it can be trapped underneath the pot and cause boggy soil conditions. Elevating the pot allows excess water to drain freely from the base of the pot and prevents the soil from being saturated. Ever since I’ve done this, I have not had any problems with root rot in any of my pot plants.
- Locate your potted petunias in an open area of full sun with good air circulation to replicate the conditions of their native environment. I like to put them at the front of my house as it is south-facing and gets lots of sunlight, meaning there are many more flowers!
- Always plant your petunia in multi-purpose compost as compost can stay moist (so that the petunia does not wilt due to drought) yet also has a porous free draining structure so that the roots are not sat in boggy conditions.
- If your petunias are planted in garden boarders, what I have done is to amend the planting area with lots of compost to create well-draining soil conditions in which petunias thrive. If your soil is naturally boggy then transfer your petunias to pots.
- Avoid planting petunias in clay soils as clay retains too much moisture for petunias to tolerate and the structure of clay soils is often too dense for petunias roots to establish properly.
- Scale back your watering schedule to once per week. Petunias are tough and fairly drought-tolerant thanks to their South American origins. If you are watering petunias every day then you are overwatering petunias and this is the reason they are turning yellow.
When I followed the best practices of care for petunias (full sun, good drainage, and watering once per week), then the soil had a chance to dry out, and my petunias recovered.
However, it is important to emphasize petunias that have been in saturated soil for a long time often die back and cannot be revived.
Lack of Fertilizer can Cause Yellowing Petunia Leaves
Petunias are not necessarily heavy feeders and often flower more in soils with medium to low fertility, as too much nitrogen can reduce flowering (from my research, this is an adaptation to the arid, sandy environment where they grow in the wild).
However, if your variety of petunia is a particularly vigorous grower, and they are in a relatively small pot (smaller pots have less capacity for soil and therefore less nutrients) or perhaps in a garden border and competing for nutrients with nearby plants then they may require fertilizer to help green the leaves and stimulate growth.
Personally, I would recommend a general, well-balanced liquid fertilizer such as miracle-gro, which contains all the nutrients at the right concentration for petunias to thrive.
Always follow the manufacturer’s instructions diligently and note that using more fertilizer than recommended does not yield better results and could reduce flowering, so always apply the recommended amount.
When I applied this fertilizer, my petunias started to recover in the next 2 weeks!
Why are My Petunias Wilting and Dying?
The most common cause of petunias dying is overwatering and damp soil, causing root rot. If root rot is the cause the leaves of your petunia are likely to turn yellow as well.
However, petunias can wilt and die back due to underwatering, heavy compacted soils, and heat stress, particularly after planting. Generally, after planting, I often see the leaves and flowers wilt slightly as the roots begin to establish.
So, how do we fix this?
Petunias require a balance of soil moisture, which is achieved by planting them in multi-purpose compost and water with a generous soak once per week.
However, there are certain factors that we need to be aware of that increase the risk of our petunias wilting due to drought stress:
- Planting petunias in small shallow pots. This is a common mistake that I see a lot! My own petunias grow well even when crowded in pots producing a display of mass flowering. However, we need to remember that really shallow pots have less capacity for soil and therefore less capacity for moisture and dry out a lot quicker.
- Compacted soils. In dense, heavy, compacted soils, the petunia’s developing root system can struggle to establish and access moisture. As we discussed, petunias require aerated compost with a porous structure that allows the roots to grow down and access water deeper in the soil, which helps them to tolerate drought. If the roots cannot grow due to heavy soil, (think about how tough clay soil is) then they stay nearer the surface of the soil, which dries out much quicker, causing the petunias to wilt.
- The use of peat compost. This is a problem I have identified from personal experience. Petunias like to grow in full sun and typically prefer being watered around once per week. The sun can cause the surface of the compost to dry out between bouts of watering. If the compost has a high content of peat, then it can bake hard and become hydrophobic, which means it repels water off the surface. Water then runs off the surface of the soil and down the side of the pot, hanging basket, or garden border without infiltrating the soil properly and reaching the roots. The lack of available moisture causes the petunias to wilt and die back.
- Intense heat and excess air flow can dry out hanging baskets in particular. I had this problem last summer due to the heat wave. Petunias prefer full sun as this promotes flowering, however, they can of course wilt due to heat waves and windy conditions sapping moisture from the leaves and soil. Petunias can resist drought and sometimes wilt temporarily to reduce the surface area of their leaves and minimize water loss before perking back up again in cooler temperatures. (Mine perk back up in the evenings after a good soak).
- Transplant shock causes wilting. It can take time for the petunias root system to become established after planting which can leave them vulnerable to drought. Also, the sudden contrast in growing conditions when they are cultivated in a greenhouse before purchase (or perhaps grown from seed yourself in a greenhouse) and the conditions of your garden can cause petunias to wilt temporarily as a sign of transplant shock. (Don’t worry as much about this one as I find it usually resolves itself).
- Watering petunias too lightly causes wilting. Whilst petunias do not typically require watering as often as other plants, they should always be watered thoroughly. If you water too lightly then only the surface of the soil is moistened. This encourages the roots to grow near the surface to access the water which causes them to be more vulnerable to drought.
My Tips for Saving Wilting Petunias
- We need to always plant our petunias in pots that are at least 12 inches across with the same proportional depth (particularly if you live in a hot climate like me). You can often get away with planting petunias in much smaller pots in cooler climates with higher levels of rainfall and more overcast days. However, larger pots are more suited to hotter climates as they can contain more soil and, therefore, retain more moisture to prevent your petunias from wilting.
- Amend the soil with lots of compost before planting petunias. Compost has a more aerated texture and retains moisture which allows the petunias roots to establish much easier after planting. If your petunias are in heavy, dense soils, what I would do is transfer them to pots and containers and replant them in compost. This allows the petunia’s roots to access moisture to prevent the leaves and flowers from wilting and dying.
- Avoid planting petunias in compost that contains any peat. I always choose peat-free compost where possible as peat compost is not only bad for the environment but also deflects water off the surface when it dries out and prevents water from reaching the petunia’s roots, causing drought stress (I found this out the hard way!). Now, I always look at the bag of any commercial compost to check it is peat-free before buying, but really, I prefer using garden compost to plant your petunias, which retains a porous structure that allows water to infiltrate and reach the roots even when the surface is dry.
- Water more frequently during heat waves and try to buffer strong winds to prevent wilting. Typically, petunias require watering once per week to maintain the optimal balance of moisture and prevent wilting. However, during heat waves, increase watering to once every 2 or 3 days to prevent wilting. Petunias prefer some airflow, but keep in mind that excessive winds can sap moisture for the leaves and cause wilting so if possible, move pots of petunias to a more sheltered location if it is particularly windy and water well so that they can recover from wilting.
- I have found through trial and error that transplant shock after planting is mitigated with good potting soil or compost, which retains moisture so that the roots can draw up water more easily as they adjust to the new soil conditions. I recommend watering once every few days after planting with a generous soak to promote good root development so that the petunia is more resistant to drought and less likely to wilt as it matures. Locate your petunias in the sun, and with careful watering, the petunias should recover from transplant shock and revive from a wilted appearance.
- Always water petunias thoroughly, rather than a light watering. A really generous soak, so that water trickles from the base of pots ensures that the moisture has reached the roots and promotes good root development, which increases the petunia’s resilience in hotter and dryer conditions and prevents the petunia from wilting.
As I mentioned earlier, my own petunias recovered (during a heat wave) from mild wilting when I gave them a good soak in the evening after the temperature cooled down.
Whilst I typically recommend watering in the morning, from my mini experiment, I found that watering wilting petunias in the evening was actually more effective at relieving them from their wilted appearance.
I think this is because when it is scorching hot during the day, the moisture can evaporate quite quickly when you water in the morning, whereas when I watered in the evening, with the lack of scorching sun and high temperatures, the water had more of a chance to soak into the soil and the roots had more time to draw up the moisture without being stressed by heat!
Typically, I find that my petunias make a full recovery from wilting after a week. This is in part due to me improving their conditions but also the pentunias had a chance to acclimate to their conditions.
Your Petunias Could be Dying Due to Cold Temperatures
Petunias are native to the warmer climate of South America and often die back due to unexpected frost or a significant fluctuation in temperature (hardy in USDA zones 9-11)
Therefore, petunias are tender and often regarded as annual flowering plants for pots, hanging baskets, and garden boarders in cooler climates.
When I lived in Southern California, in my hot climate my pentunias would last all year but When I moved to New York, I had to treat them as annuals.
My petunias died back as the temperature cools in Fall or Winter and sometimes die in Spring due to late Spring frosts.
Pro tip: Now that I live in a cold climate where there is a threat of frost then I grow petunias in pots or hanging baskets and I move them into my garage, (a heated heated greenhouse works well too), until the threat of frost has alleviated. Always place them in some light if you can.
Of course, you can also try horticultural fleece, which can also help protect cold-sensitive petunias from cold nights and occasional frost, which can help if they are planted in garden borders and cannot be easily moved indoors for protection from the cold.
Remember that our Petunias Require Full Sun!
If your petunia has poor, leggy growth with few flowers and a dying appearance, then it requires more sun.
We must consider that petunias are adapted to growing in open areas, in warmer climates of South America, and prefer at least 6 hours of sun to display the best flowers.
To ensure your petunias are as healthy as possible and display flowers, it is important to plant them in the sunniest area of your garden.
More hours of sun also help mitigate the risk of root rot and mold by creating a dyer environment for your petunias to thrive.
Honestly, in my experience, most petunia can be saved by moving them into full sun and getting the watering right.
Move petunias in pots, containers, or hanging baskets to an area of full sun and help revive your petunias and new healthy growth with more flowers should emerge over the next few weeks.
Why is My Petunias Turning White?
The reason petunias turn white is because of mold or powdery mildew, which is caused by high humidity, watering late at night rather than morning, and a lack of air circulation.
This one happened to me, and I had to do a mini-experiment to find the cause. I had several pots of petunias around my garden (as well as lots of other potted plants). Typically, I watered half of my garden in the morning and the other half in the evening because there were so many pots!
It was the potted petunias that I watered in the evening that suffered from the powdery mildew, as you might expect!
So, the solution?
Always water your petunia in the morning as this charges them with moisture before the sunny day ahead and gives any moisture a chance to dry out in the sun before the cooler evening.
If you water too late at night, then the petunia has to sit in damp and humid conditions for longer, which encourages powdery mildew, which has a white appearance on the leaves.
Of course I would put the cavet on this as I discussed earlier in this article that in the specific cirmcumstance of heat waves, I actually found it more beneficial to water in the evening to give the water a good chance to soak in.
Any time outside of a heat wave I water my petnuias in the morning.
I think this just shows you how reactively we have to be to our environment to look after our petunias!
Petunias are also acclimated to growing in open areas with good airflow from occasional breezes. If they are in a closed location, particularly with high humidity then they are more at risk from turning white due to powdery mildew.
I must caution against using any fertilizer if your petunia leaves are turning white, as powdery mildew tends to affect lush green growth more than established leaves.
Powdery mildew does not necessarily harm petunias to any great extent, and petunias often flower relatively unaffected. Read this article to learn more about treating powdery mildew.
Petunias in full sun, with good airflow, and watered before a hot day so that water on the leaves can evaporate tend to cope better with powdery mildew than unhealthy plants that are not in optimal conditions for growing petunias.
Key Takeaways:
- The reason for dying petunias is usually root rot caused by excess moisture around the roots from overwatering. Petunias should be grown in well-draining compost and watered once per week to avoid dying of root rot. In boggy soils, petunias wilt and turn yellow with a dying appearance.
- Overwatering, not enough sun, and a lack of nutrients can all cause petunia leaves to turn yellow and die back. Petunias require at least 6 hours of sun to flower and prevent yellowing leaves. Petunias in small pots can turn yellow due to small pots containing less soil and, therefore, fewer nutrients. Use a fertilizer to prevent the leaves from turning yellow. Only water petunias once a week and ensure well-draining conditions to prevent yellowing leaves from root rot.
- Petunias can also wilt because of drought stress. In hotter climates, petunias often wilt if they are planted in shallow pots or hanging baskets as they have less capacity for soil and, therefore, retain less moisture, which causes the petunia to wilt as a sign of drought stress.
- To revive a dying petunias, ensure that the soil is moist but drains efficiently. This is achieved by watering petunias thoroughly once a week and planting in well draining compost. Locate petunias in full sun with good airflow to help them revive.