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Astilbe is a popular perennial known for its beautiful, feathery flower plumes and lush foliage. Growing healthy astilbe starts with proper care of seedlings, especially during the hardening off process before planting them outdoors. Hardening off helps seedlings adapt to outdoor conditions, reducing transplant shock and promoting vigorous growth.
Understanding Hardening Off
Hardening off is the gradual process of acclimating indoor-grown or greenhouse seedlings to outdoor environments. It involves exposing plants to outdoor conditions for increasing periods over several days. This process strengthens seedlings, making them more resilient to wind, sunlight, temperature fluctuations, and other outdoor stresses.
When to Start Hardening Off Astilbe Seedlings
Begin hardening off astilbe seedlings about one to two weeks before the scheduled planting date. Wait until the outdoor temperatures are consistently above 50°F (10°C) at night and the risk of frost has passed. Early spring or late spring is usually the best time to start this process.
Signs That Your Seedlings Are Ready
- Seedlings are healthy and vigorous indoors.
- Outdoor conditions are suitable and stable.
- No frost or freezing temperatures are forecasted.
Steps for Hardening Off Astilbe Seedlings
Follow these steps to successfully harden off your astilbe seedlings:
- Day 1: Place seedlings outside in a shaded, sheltered spot for 2-3 hours. Protect from direct sunlight and strong winds.
- Day 2-3: Increase exposure to 4-6 hours, gradually introducing morning sun.
- Day 4-5: Extend outdoor time to 8 hours, including some afternoon sun if conditions are stable.
- Day 6-7: Leave seedlings outside overnight if temperatures remain above freezing.
- Beyond Day 7: Gradually expose seedlings to full outdoor conditions, including full sun and wind, for longer periods each day.
Ensure that seedlings are kept well-watered during this process and protected from harsh weather such as heavy rain or strong winds. Bringing them back indoors during extreme weather helps prevent damage.
Additional Tips for Successful Hardening
- Choose a sheltered location, such as near a wall or under a tree, to reduce wind stress.
- Monitor weather forecasts and avoid hardening off during cold snaps or storms.
- Use shade cloth or row covers if outdoor sun is too intense initially.
- Ensure good air circulation around seedlings to prevent fungal diseases.
Transplanting Astilbe Seedlings
Once seedlings are fully hardened off and outdoor conditions are suitable, transplant them into your garden. Choose a location with rich, well-draining soil and partial shade to full sun, depending on your climate. Space plants about 1 to 2 feet apart to allow for growth. Water thoroughly after planting and mulch to retain moisture.
Properly hardened seedlings will establish quickly and flourish, providing vibrant blooms and lush foliage. Regular watering, mulching, and occasional feeding will support healthy growth throughout the growing season.