Answer: Snapdragons do best in a rich soil that is moist yet well drained (meaning not soggy) and in a full sun location. This would mean about six hours of full sun including the hour of noon as a minimum, so it is possible they are in too much shade and the soil is too damp. It is better to water less often but deeply than to water daily. The longer interval encourages roots to grow deeper where the soil naturally stays moister longer. Finally, as the flowers fade the blooms stems should be trimmed off just below the current flowers. This allows new side shoots of fresh blooms to develop.
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