Starting seeds indoors offers a cost-effective way to grow a variety of vegetables and ornamental plants. This method allows gardeners to cultivate seedlings that can be transplanted outdoors, following a general process adapted to each plant’s particular needs for seed depth, growing medium, water, and light. Key steps include selecting a suitable container, ensuring adequate light for seed germination, maintaining proper moisture levels, and hardening off seedlings before transplanting them outside. By mastering this process, you’ll soon enjoy a thriving garden filled with home-grown fruits, vegetables, and flowers.

When to Start Seeds Indoors

Seed packets often indicate if a plant should be started indoors, with instructions like “start indoors eight weeks before the last frost date.” A simple internet search will tell you the date of the expected last frost in your area. Count backward to, for example, eight weeks before that, and that’s the date you should start your seeds.

Not all plants should be started by seed indoors because they are better grown by sowing seeds directly in the garden. Root vegetables, like radishes and beets, and row crops, like beans and corn, simply don’t transplant well. Other crops—like cucumbers and zucchini or flowers like zinnias and sunflowers—germinate so quickly that starting by seed early has no real advantage. To direct sow seeds, follow the seed packet’s instructions, which provide a planting date range based on the last frost dates in each USDA hardiness zone and recommended soil temperatures.

Reading a Seed Packet

The printed instructions on the back of a seed package will give you a lot of information on how (and if) you should start the seeds indoors. These elements are among the most important information to look for:

• Planting time: Most seed packets will tell you quite clearly if the seeds can or should be started indoors. For some species (tomatoes, for example), it is virtually mandatory to start seeds indoors in cold-weather climates. For other species it may be optional, and for other fast-growing species, there may be no indoor starting information at all—these plants are best planted directly in the outdoor garden.
• Days to maturity: This will tell you how long the plants take to produce edible fruit or ornamental flowers. Some tomato plants take as much as 100 days to reach fruit-producing maturity. If you want tomatoes in July, this means the seeds need to be started in early April.
• Light and water needs: The seed package will tell you if the seeds need lots of light. If so, starting them indoors may require a fluorescent grow light—or you may need to reserve your sunniest window for seed-starting.
• Soil needs: Some seeds can be started in ordinary potting soil, while others require a porous, fine-grained seed-starting mix. The package may also suggest an optimal soil temperature for seeds to germinate. Seeds that require 70-degree soil to germinate will clearly need to be started indoors in cold-weather climates since the soil does not get adequately warm until late into May.

The seed package will also give a wealth of other information, such as days to germination, fertilizing needs, planting depth, and transplanting techniques.

Before Getting Started

There are many good commercial potting mixes available that are suitable for starting seeds. Although they may be called “potting soil,” they actually contain no garden soil at all. Instead, they are soilless mixes containing materials such as peat moss, perlite, vermiculite, compost, and more. This ordinary potting mix is fine for starting many seeds.

Some seeds—especially those that are small—may do better in what is known as a seed-starting mix. Seed-starting mix is a special form of soilless potting mix that is especially porous and fine-grained. It omits the organic materials found in standard potting soil. This is because seeds do not require the nutrients provided by organic material to germinate and sprout.

For many plants, a seed-starting mix is the best choice, because the organic material in a standard potting mix can lead to fungal problems. Avoid starting your seeds in outdoor garden soil, which can become compacted. And outdoor soil often contains weed seeds and disease pathogens that interfere with seeds germinating and sprouting.