When Do You Transplant a Seed That Has Sprouted?

Temperature Needs

• Transplanting temperatures vary depending on the type of plant, but most seedlings require transplanting after frost danger has passed in spring and the soil has warmed. Heat-loving seedlings, like peppers (Capsicum annuum) are best transplanted about two weeks after the last frost, or when soil temperatures have warmed to at least 60 degrees Fahrenheit. You can transplant frost-tolerant plants, like broccoli (Brassica oleracea), two to four weeks before the last expected frost. The seed packet lists the best time to transplant most seedlings, but generally waiting until after the last average spring frost date works for most perennials, summer vegetables and annual flowers.

Seedling Maturity

• Seedlings require some time indoors before transplanting to develop healthy roots and sufficient leaves to support the plant. For most plants, four to six weeks of indoor growing after germination provides sufficient time for healthy development. If the seedlings have a strong stem and have produced at least two true leaves, which are the leaves grown in after first set, it's likely mature enough to survive outdoors. Waiting too long results in a rootbound plant as the roots grow too large for the seedling pot.

Hardening Off

• Preparing the seedlings for transplant requires an additional week to 10 days of hardening off, but this increases the plant's chances for survival and minimizes shock after transplanting. To accustom seedlings to the outdoors, set them outside in an area protected from direct sunlight when temperatures are above freezing or in the recommended range for the plant variety. Move the plants into a more exposed area gradually over the hardening period, until the seedlings are fully exposed for the entire day by the end of the week. If frost is expected, bring the seedlings indoors. You can also bring them in at night to protect them from lower temperatures and night-feeding pests.

Transplanting Tips

• After determining your transplant time and hardening off the seedlings, you can plant them in their permanent location. Preparing the garden bed first further helps ensure successful growth. Most plants benefit from the addition of 2 inches of compost mixed into the top 6 inches of soil. You might also need to add fertilizer, depending on the nutrient needs of the plants. Plant most seedlings at the same depth they were growing at in their seedling pots, and space them at the appropriate distance recommended for the plant variety. Water the plants deeply immediately after transplanting so the soil is moist throughout the root zone. This prevents initial drought stress and settles the soil around the roots.