(Image credit: Konoplytska)

Annuals are typically tropical or other warm-weather plants that don’t survive the winter in many gardens. Knowing when to plant annuals outside for the growing season essential to their survival. Check the average last frost date for your region to time it right. 

When Can Annuals Be Planted Outside? 

If you started annuals from seeds, they’re ready for transplanting once you see the first true set of leaves. The two little leaves that appear first on a seedling are not true leaves. They are called cotyledons. 

Of course, you also need to consider the weather. The seedlings might be ready, but the weather must cooperate, or they will die outside in the cold. Check with your local extension office to find out your area’s average last frost date. This is the average day on which you get the final frost of the spring season. Of course, it varies each year, but the average is a useful guide. 

The best time to plant annuals is generally after the average last frost date. Pay attention to the forecasts to determine if you need to wait longer. If transplanting to containers, you can plant them earlier and bring the pots indoors if there is a risk of frost. 

How to Plant Annuals

When it comes to annual planting, flowers benefit from some hardening off before going full time outdoors. They have been enjoying the gentle indoor climate of your home or the garden center and can suffer damage if shocked by cold, wind, and sun. 

Place them outside in the shade for a few hours a day, then in the sun for a few hours. After a week, they’re ready to go. When it’s time to transplant, do it on a cloudy day or in the evening to ease the plants into a new environment. 

Turn the soil where you’ll be planting the annuals and add some organic material. Follow depth and spacing instructions for each type of annual. Generally, you want the plants to be situated to a depth similar to how they sat in their starter containers. Water the plants in their cell packs in advance of placing them in the ground and let them drain. 

Water your new transplants regularly as they get started growing. Generally, annuals need about an inch (2.5 cm.) of water per week, but more in the beginning helps them grow strong roots. Add a fertilizer or bloom booster about two weeks after transplanting. 

Start pruning early as well to prevent your plants from getting spindly and leggy. Pinching off new growth early promotes fuller growth and a healthier plant throughout the season. 

Mary Ellen Ellis

Mary Ellen Ellis has been gardening for over 20 years. With degrees in Chemistry and Biology, Mary Ellen's specialties are flowers, native plants, and herbs.