The brightly-coloured large blooms of petunias are often found in flower pots, gardens or decorating the edges of walls or fences throughout the summer. Although petunias are relatively easy to care for, they are not without their share of issues. Fungus, deficiencies and problems with the soil can all take your petunias from thriving to failing. Saving your petunias from certain death is a matter of determining the problem, then treating it.
Spray a fungicide on the petunias, if you suspect fungus is causing the issues. Leaves that turn black or brown are a common sign of a fungal problem. Fungicides are often sprayed directly onto the plant; however, read the directions for best results. When watering, only make contact with the soil, not the plant.
Test your soil's salt content, if your petunias have white spots. Collect a sample of the soil and take it to your local extension for testing. Add sphagnum peat moss to your soil to dilute the salt content, if it is indeed too high. Replace about half of the soil with the peat moss.
Give your petunia fertiliser, if the outsides of its leaves are turning yellow. This colour change often enters the main stem, as well. Use liquid or granulated fertilisers made for petunias. Many are added into the water or placed in the soil; however, read the directions on your product's label for best results, as they can vary by brand.
Reduce the amount of water you give your petunia if its leaves go limp or curl. Petunias that experience such issues are typically watered too much and often have fungal problems. Insert your finger into the soil down to the second knuckle. Pull it out and take a look. Water your petunias if your finger comes out clean. Skip watering if soil remains on your finger. Applying a fungicide to the petunia will also likely help.
Always plant your petunias in sterile or pasteurised soil. If planting your petunias in pots, use those that have drainage holes. Additionally, always look at the plant's label for information on sun requirements and follow them. Doing so can help you to grow a happy and healthy petunia.