So you’ve decided to start seeds indoors for outdoor planting. Although starting seeds indoors takes more effort than buying transplants, your diligence will be rewarded with an abundance of healthy plants at a fraction of the price of nursery seedlings. The trick in starting seeds indoors is to produce healthy seedlings that reach 2 to 4 inches tall at the right time to plant outdoors. If started too early, the seedlings become leggy and unhealthy from an extended period indoors. If started too late, the seedlings won’t be mature enough to plant and your harvest may be delayed.
Many gardeners wonder when to plant seeds for outdoor growing, and the answer depends on several factors. First, seeds vary in their average germination and growth times. Annual flowers, such as geraniums, impatiens, pansies and lobelia, germinate and grow slowly, needing between 12 and 15 weeks indoors before transplanting. Start petunias, vinca, black eyed Susan, sweet alyssum and verbena 9 to 11 weeks before planting outdoors. Baby’s breath, nasturtium, marigold and bachelor buttons are the sprinters of the plant world, growing in five to six weeks.
Vegetables take between 5 and 10 weeks from seed sowing to transplanting. Broccoli, cabbage and head lettuce need around 10 weeks, while tomatoes need only five. Keep in mind that some vegetables, such as corn, beans and pumpkins, don’t like to be transplanted and are better off sown directly in the garden once soil temperatures warm in early summer.
In planning when to start seeds, it’s crucial that you understand the proper time to plant them outdoors. Many hardy annuals, such as pansies, bachelor buttons and sweet peas, tolerate and even prefer cool outdoor temperatures, and can safely be planted outdoors in early spring. Other annuals and most vegetables need warm, frost-free weather to thrive. Check PlantMaps.com if you are unsure of your area’s last average frost date.
Check out this handy chart from Johnny’s Selected Seeds where you can input your last frost date and it calculates the dates for when to start the seeds and when to set the plants outside.
You can increase your chances of success by keeping the germination conditions optimal. Most vegetables germinate best when soil temperatures are between 65 and 85 degrees Fahrenheit. Keep your seeds in a warm spot and make sure the soil is adequately moist to hasten germination. Once the seeds germinate, move them to a cooler location that receives at least eight hours of sunlight per day.
If you are growing many different plants, make some field notes on each season’s germination rates and best outdoor planting times. Keep track of your notes from year to year and you’ll soon have a well-organized system for starting seeds indoors.
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