Petunias are tender annual flowering plants that do not tolerate frost or cold temperatures and die back in Winter.
Dying and wilting petunias are usually because of fungal diseases such as root rot, caused by excess moisture around the roots. Petunias require a 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 it is important 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 dying and how to revive your petunias so that they recover and displays 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 over watering, slow draining soils and pots without drainage.
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 disease such as root rot and Botrytis which thrive in damp, slow draing 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
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).
Petunias are relatively hardy to somewhat dryer conditions and can even tolerate drought once they have established.
The schedule of watering generously once per week and allowing the soil to not become too boggy emulates the typical watering cycle of the petunias 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. Some decorative pots do not have drainage holes in the base or the holes become blocked with compacted soil and prevent water draining effectively.
- Trays underneath, pots or containers. Petunias grow exceptionally well in pots due to their favorable drainage conditions. However if you place the pot on a tray to prevent water spilling then this 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, some hanging baskets are line with a plastic impermeable sheeting or other material which can help retain moisture, but could be preventing water escaping from the bottom of the basket. This can cause the boggy soil which turns petunia leaves yellow with a drooping appearance.
- Watering too often. If you are watering petunias everyday then you are watering far too often. Scale back the watering to once a week and only increase watering 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 is suffering with 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.
How to Revive Petunias With Yellow Leaves
- If your petunias are turning yellow in a hanging basket, check to see if there is a plastic membrane (and remove it) that may be preventing water from draining efficiently to help improve drainage.
- 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 repot 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 to prevent any blockages to the drainage holes.
- 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.
- Locate your potted petunias in an open area of full sun with good air circulation to replicate the conditions of their native environment.
- Always plant your petunia in multi purpose compost as compost is able to 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, always 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 root 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 your are overwatering petunias and this is the reason they are turning yellow.
If you follow the best practices of care for petunias (full sun, good drainage and watering once per week) then the soil should have a chance to dry out and the petunias can recover.
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.
However if your variety of petunia is a particularly vigorous grower, and they in a relatively small pot (smaller pots have less capacity for soil and therefore less nutrients) or perhaps in a garden boarder 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 manufactures institutions diligently and note that using more fertilizer then recommended does not yield better results and could reduce flowering so always apply the recommended amount.
With some well balanced fertilizer, your yellow petunias leaves should show signs of recovery in the following weeks.
Petunias Wilting and Dying
The most common cause of petunias dying is because of overwatering and damp soil causing root rot.
However petunias can wilt and die back due to underwatering, heavy compacted soils and heat stress, particularly after planting.
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 which increase the risk of your petunias wilting due to drought stress:
- Planting petunias in small shallow pots. Petunias can grow well even when crowded in pots producing a display of mass flowering. However in 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 petunias developing root system can struggle to establish and access moisture. 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 then they stay nearer the surface of the soil which dries out much quicker, causing the petunias to wilt.
- The use of peat compost. 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 boarder 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. 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.
- Transplant shock cause 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 green house prior to purchase (or perhaps grown from seed yourself in a green house) and the conditions of your garden can cause petunias to wilt temporarily as a sign of transplant shock.
- 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.
How to Revive Wilting Petunias
- Plant your petunias in a pot that is at least 12 inches across with the same proportional depth if you live in a hot climate. 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 a larger pot is more suited to hotter climates as it 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, the best thing to do is to 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. Choose peat free compost where possible as peat compost is not only bad for the environment but it also deflects water off the surface when it dries out and prevents water from reaching the petunias roots causing drought stress. Look at the bag of any commercial compost to check it is peat free before buying or use 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 air flow, 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.
- Transplant shock after planting is mitigated with good potting soil or compost which retains moisture so that the roots can draw up water easier as they adjust to the new soil conditions. Water once every few days after planting with a generous soak which promotes 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 petunia should recover from transplant shock and revive from a wilted appearance.
- Always water petunias thoroughly, rather then 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 petunias resilience in hotter and dryer conditions and prevents the petunia from wilting.
A dying petunia with wilting leaves should recover from drought within a week as long once you create the right conditions with good moisture retaining compost and watering thoroughly at least once per week to promote stronger roots for more drought resistant petunias.
Petunias Dying in Cold Temperatures
Petunias are native to the warmer climate of South America and often die back due to unexpected frost of a significant fluctuation in temperature (hardy in USDA zones 9-11)
Therefore petunias are tender and often regarded as an annual flowering plant for pots, hanging baskets and garden boarders in cooler climates. Petunias die back as the temperature cools in Fall or Winter and sometimes dies in Spring due to late Spring frosts.
If you live in a cold climate where there is a threat of frost then grow petunias in pots or hanging baskets so that you can move them into a garage, or heated greenhouse, until the threat of frost has alleviated.
Horticultural fleece can also help to protect the cold sensitive petunias from cold nights and occasional frost which can help if they are planted in garden boarders and cannot be easily moved indoors for protection from cold.
Petunias Require Full Sun
If your petunia has poor, leggy growth with few flowers with a dying appearance then it requires more sun.
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 you petunias are as healthy as possible and display flowers, it is important to plant them in the sunniest area of your garden.
The more hours of sun also helps to mitigate the risk of root rot and mold by creating a dyer environment for your petunias to thrive.
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.
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 then morning and a lack of air circulation.
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 encourages powdery mildew which has a white appearance on the leaves.
Petunias are also acclimated to growing in open areas with good air flow 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.
Avoid using any fertilizer if your petunia leaves are turning white as powdery mildew tends to affect lush green growth more then 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 then unhealthy plants that are not in optimal conditions for growing petunias.
- 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 less nutrients. Use a fertilizer to prevent the leaves 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 retains 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.