Deadhead petunias by cutting off dead flowers, trimming the flower to the stem, spacing out the deadheading and pruning the plant in mid-summer. Fertilize the petunia plants after pruning and deadheading them. You need pruning shears or pruning scissors and fertilizer.Continue Reading
Find sharp scissors or pruning shears to use. If the shears are not clean, let them soak in a mixture of water and alcohol for several minutes.
Trim off withered and dead flowers down to the stems. Make sure to remove the seedheads and all parts of the old flowers so that the energy of the plant goes into producing new flowers and not into developing seeds.
Do not deadhead or trim the petunias more than once a week to allow the plant to recover. However, do deadhead the flowers regularly to encourage growth and flowering.
Prune the plant more heavily in the midsummer. Cut it down to half its length. This keeps the flowers from getting too scraggly and encourages growth later on in the growing season.
Immediately after deadheading or pruning the petunia plants, apply a 10-10-10 fertilizer. After fertilizing the plants, water them.