Answer: If you cut off the flowering stalk when the flowers fade on your snapdragons, they will send up a new flower stalk before the season ends. The flowers start to fade on the lowest part of the stalk first, so pinch those off before they set seeds but allow the rest of the flowers to open. When they have all opened, you can cut the entire flowering stalk down to just above the foliage and your plant should produce a second, smaller, flowering stalk. To keep petunias flowering all season long, pinch off the spent flowers plus some of the stem. Wherever you pinch petunia stems they will branch out into two new stems. If you do this all summer the plants will remain compact (rather than get leggy) and the will produce lots and lots of flowers.
Best wishes with your garden!
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