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For growing asters, the soil should be moderately moist with well-drained soil to wet soil, never flooding, for best flower production. Make certain the plants receive water during drought conditions. Try to keep water from the leaves because asters are susceptible to leaf fungus.
No need to fertilize if asters are planted in decent soil that is mulched year round. Too much nitrogen promotes excessive foliage growth and floppy stems. A light sprinkling fertilizer on the soil each spring is sufficient. For more information see file on Choosing Fertilizers.
Spread a 2 to 4 inch layer of some attractive organic material on the soil around the asters to protect their roots. Wood chips, chopped leaves, or shredded bark by themselves or over landscape fabric will discourage weeds and help retain moisture in the soil. A good mulch can reduce the rate of soil moisture loss by as much as 50 percent, depending on the material used. For more information see file on Using Mulch.
May need staking, especially the taller New England aster and most plants if they haven’t been pinched Pinch taller types starting in June or July to reduce need for staking and stimulate blooming. Cut stems back by one-half in June and again in late July to delay bloom for 2 weeks but plants will be more compact. ‘Alma Potschke’ does not need pruning to stimulate lots of blooms.
When asters have finished blooming, cut off the flower heads before the seeds mature and (drop)to the ground. When the growing season is complete, cut aster back to the ground.
Winter Protection for Asters
Spread fresh mulch for winter protection. For more information see file on Winter Protection for Plants.