If you are overhead-watering (garden beds), try and water in the early morning so the flowers have time to dry out through the day. Mulch helps keep moisture in the soil by inhibiting evaporation. Use mulch on both beds and container-grown petunias to retain as much moisture as possible in the soil.
To test whether or not your petunias are ready to be watered, stick your finger down into the soil to the depth of your first knuckle. If it feels dry, it's time to water. Once you've had some practice, you'll be able to tell by the weight of your planter whether or not the soil is dry.
Regular watering is important and is vital for petunias growing in pots and containers. The compost mustn't be allowed to dry out, but at the other extreme, take care not to over-water, either, as this can cause spindly growth. Petunias growing in the ground also need watering during dry spells.
Petunias are subject to root and crown rot, a result of uneven watering. “Like pansies,” she says, “petunias must never be allowed to wilt, either from under- or overwatering. Once they wilt, it's all over.” She advises providing good soil conditions, including preparation with organic materials and ample mulching.
Morning watering is actually preferable to evening watering as the plant has time to dry before the sun goes down. At night, water tends to rest in the soil, around the roots, and on the foliage, which encourages rot, fungal growth, and insects.
Water your plants in the morning as early as possible. This allows the soil and your plants to absorb more water because in the heat of the day there is more evaporation occurring at the soil surface. Drip irrigation is ideal because it deposits water directly at the soil surface and can be targeted.
The best time to water plants is in the morning or evening.
More importantly, watering at these times actually helps the plant retain water. If you water in the afternoon, especially during summer, the heat and sun are at their peak and the plant's water will evaporate instead of absorbing into the soil and roots.
Although Petunias are very easy to grow and have few maintenance challenges, there are some common pests that plague these sun lovers. All types of aphids (whitefly, greenfly, and blackfly), tobacco budworm, rose slugs, western flower thrip, and cyclamen leafminer can affect the appearance and growth of Petunias.
Hanging baskets dry out quickly, so it's important to check them frequently. If the soil feels dry 1-2 inches down, then it's time to water. During hotter weather, this may mean watering once or twice a day. In cooler weather, reduce the amount of water and don't allow soil to remain soggy.
Miracle-Gro Water Soluble All Purpose Plant Food, Plant Fertilizer for Indoor or Outdoor Plants, Roses, Flowers, Houseplants, Vegetables and Trees, 10 lb. Miracle grow is the best for petunias.
Using Epsom salt on petunias is popular. Some think adding it to garden soils and potted plants helps promote growth and improve the overall production of flowers.
Spotting the Signs of Overwatered Petunias
Yellow, swollen leaves are the red flags of overwatering. If the soil feels like a swamp, you've gone overboard with the watering can. Root rot and a general look of despair in your Petunias are also telltale signs.
The secret to growing good petunias is to feed, feed, feed. You'll get even better results if you use a specialist fertiliser. T&M's high quality petunia fertiliser granules release a constant, controlled supply of nutrients without wastage or leaching.
Petunias are adaptable plants that can thrive in the ground or planters. Their relatively easy care requirements and abundant flowers make Petunias a very popular choice for containers and hanging baskets.
You may need to trim the plants back to within an inch or two of the base. Water your petunias thoroughly and keep the soil evenly moist. A flush of new growth will soon appear and produce new blooms. Within a few weeks your petunias will return to their previous vigor, as long as you keep them watered well.
Except for "spreading" types, which require frequent watering, thorough watering once a week should be sufficient in all but the worst weather. Leave sprinklers on long enough to soak the soil to a depth of 6 to 8 inches every time you water.
Deadheading Tips
The dying flowers of summer bedding plants such as marigolds and petunias, can be simply pinched off between finger and thumb, just below the base of the flower. Alternatively, use scissors or florists' snips.
The spicy sweet petunia petals are very appealing and quite edible. Most likely squirrels are eating them. The bad news is that while you can apply a number of things to discourage them from eating them, nothing stops a squirrel for long.
Vinegar as a disease control: What a great idea! Spray something that kills plants onto your prized petunias to control disease! OK, when you use vinegar as a plant disease control you do use a lower concentration which shouldn't hurt the plant.
Tobacco budworm feeds on the buds and petals of many commonly grown flowers, including geranium, petunia and nicotiana. Damage tends to be worst following mild winters when soil does not freeze deeply.
Try not to water at night. Night-time watering is not ideal because your plants' leaves may not be able to dry off as quickly as other times of day. Wet leaves are more susceptible to diseases. That said, water your plants the moment you notice they look wilted.
Answer: Early morning (5:00 to 9:00 am) is the best time to water the garden when using a sprinkler, garden hose, or any other device that wets the plant foliage. When watering is completed, the plant foliage dries quickly. The rapid drying of plant foliage helps guard against the development of fungal diseases.
Don't Water at Mid-Day in the Sun. "Don't Water Your Plants in the Middle of the Day!" How many times have you heard that? "Only water your plants in the early mornings or late evenings." THE CHALLENGE: That's easy to say, but not always easy to do.