Starting Seeds

Starting seeds is a garden rite of spring (and other seasons), but you might not know where to start.

Do your seeds need to be soaked? Stratified? Or, scarified? Let’s find out.

Newly planted seeds (Kate Russell)

Seed basics

Most seeds are surrounded by a hard hull or seed coat. The seed coat protects the embryonic seedling and its food supply (endosperm) from moisture, pests, and disease. Rising temperatures and spring rains soften the seed coat, allowing moisture to enter and triggering the new plant into reaching for the sun. Before they do that, many seeds need to go through a period of winter rest before they can successfully sprout in spring. Some seeds, such as lettuce and dandelions, have evolved to be blown on the wind, landing lightly where they fall, while others need to be buried deeply in cold, damp soil – think acorns and squirrels.

The inside of a Ginkgo seed, showing healthy embryo, endosperm, and seed coat (Curtis Clark) CC BY-SA 2.5

If you plant a seed before it gets warm enough outside, odds are pretty high that the seed will either rot in the ground, or it will never really thrive. Understanding each plant’s unique ideal sprouting and growing conditions will help you start seeds more successfully.

Most vegetables

Most garden seeds will germinate when temperatures reach 60°F to 70°F if they are planted in loose, moist soil at the proper depth. The general rule of thumb for seed planting depth is to use twice the seed width or diameter. This means a seed that is ¼” wide should be planted ½” deep. Too often, seed packets rely on a standard planting depth, which is not always in a seed’s best interest. If you will be planting a lot of seeds, you may want a dibble.

Heat lovers

Okra, pumpkin, and squash seeds need a lot of heat (85°F to 95°F) to have a good start. This group is followed closely by beans, eggplants, and watermelons (75°F to 85F). [You can email me for a free chart of ideal temperatures for germination.]

Okra (elouis73) Pixabay

​Light likers

This group needs to be covered with soil, but only a little. It includes broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, cucumbers, eggplant, kale, kohlrabi, leeks, melons, peppers, squash, and tomatoes.​

Light lovers

Some seeds need light to germinate. If they are hidden away under the soil, they will sit there until they rot. This group includes chamomile, lemon balm, lettuce, and savory. To plant light lovers successfully, moisten the soil thoroughly first. Then press the seeds into the soil and use a mister to keep them moist until they germinate. Your watering can or hose will flood these tiny seeds into a corner where they will cluster and get moldy.

Cold, wet winter types

Romaines and other lettuces (Kate Russell)

​Seeds to soak

Some seeds are more likely to germinate and grow well if they are soaked overnight before plantingOther seeds need periods of cold, wet stratification. It is called stratification because, traditionally, these seeds were soaked for 24 hours and then layered in a cold, moist growing medium until they germinated.

​These are your cool-season crops that germinate best when temperatures are in the 45°F to 50°F range. This group includes members of the cabbage family, carrots, collards, Echinacea, leeks, lettuce, onions, parsley, parsnips, peas, spinach, salsify, and turnips. While most herbs prefer warmer temperatures borage, chamomile, chervil, cilantro, dill, marjoram, and thyme will germinate better at these cooler temperatures.

Hawthorn seeds stratified in sand (Gmihail) CC BY-SA 3.0

This group includes asparagus, beans, beets, carrots, corn, okra, parsley, peas, pumpkins, squash, and Swiss chard. Do not soak seeds for more than 24 hours or they will rot.

Seeds to scratch

Some seeds have evolved for a more rugged life. Often, these are seeds that, in nature, end up going through someone’s digestive tract before being deposited on the ground with a convenient pile of fertilizer. If you scratch or nick the surface of your bean, melon, and squash seeds, and then soak them overnight, you can significantly increase germination rates. Just be sure that you do not puncture the seed coat as this can kill the embryonic plant. Just rough it up a little. This is called scarification.

Mechanical scarification of acacia seeds using a rasp (Gmihail) CC BY-SA 3.0 Serbia

Transplant trauma

Once your seeds germinate and start to outgrow their first home, you will need to transplant them. Transplanting is extremely stressful. Root hairs get torn away, everything starts drying out, and getting reestablished takes time. Some plants really hate being transplanted. This group should be planted directly where you want them to grow, if at all possible, and it includes anise, arugula, borage, carrots, chervil, cilantro, dill, fennel, mustard, parsley, parsnips, peas, radish, rutabaga, spinach, Swiss chard, and turnips.

Other plants, such as beans, corn, cucumbers, melons, and squash, grow so quickly that it’s just easier to plant them where you want them.

If you start your seeds indoors or in an otherwise protected area, you will need to harden off seedlings. Hardening off refers to gradual exposure to the sun, wind, and various temperatures. Plants don’t take kindly to shocks.

Use these tips to get the most out of your seed planting efforts:

• wait until temperatures are warm enough
• choose varieties suited to your microclimate
• start with certified disease-free seeds and clean containers
• read the seed packet label
• plant seeds at the proper depth in sterile, loose, fine-textured soil
• label the pots – seriously, you’ll thank me later
• cover the seeds and soil lightly with vermiculite (unless it’s a light lover)
• keep the soil moist but not soggy until seeds germinate
• once germination occurs, allow the soil to dry out between waterings

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What seeds are you starting?