Starting from Scratch: The Miracle of Seeds

Feb 9, 2024

Starting from Scratch: The Miracle of Seeds

Feb 9, 2024

Growing your own plants from seed has a lot of advantages: more variety, less cost and getting a head start on the growing season are just a few. Practicality aside, it's just plain miraculous to grow plants from seeds. The process of putting hard, dry, seemingly lifeless bits into soil and seeing the transformation to a living plant is fun, fascinating, and forms an amazing connection to the natural world.  Some seeds can be sown directly into the ground, but others benefit from a gentler, more controlled beginning and February is the perfect time to get started. If the rows of colorful seed packets are enticing but the idea of growing anything from seed seems daunting, fear not. If previous attempts have been disappointing, fear not. Here's what you need to know to get growing:

 How Seeds Work

It can be as big as a coconut or as small as a speck of dust, but every seed is a plant waiting to happen. On the outside is a protective covering known as a “coat.” On the inside is the “germ,” a tiny embryonic plant with a root, stem and one or more leaves. Surrounding the germ is nutritive tissue or “endosperm,” which sustains the incipient plant.

When soil temperature is right and sufficient moisture is available, the seed coat allows water and air to infiltrate, and the germination process can begin. 

A tiny stem stretches upward, the Cotyledons unfold, turn green and disappear once the plant develops true leaves.

 What Seeds Need

Three things are needed for germination: the right temperature, abundant moisture and sufficient oxygen. Too much or too little of any one of these factors will not lead to success.

Choices, choices

Unlike commercially grown seedlings, which are usually available in only one or two varieties, growing from seed gives you a much wider selection of varieties and allows you to select plants for conditions in your location.  When selecting tomatoes and other seasonal crops, pay close attention to “Days to Maturity,” the term for the number of days it will take to produce fully ripened or mature produce.  Varieties with fewer days to maturity are best for cooler, foggier areas. Be sure to use seeds from a reputable supplier and check the expiration date before purchase.

Plan Ahead

Decide the number of plants you want to end up with when your seedlings are ready to transplant. Factor in that some seeds will fail to germinate and that some seedlings will not be sufficiently robust to “graduate” to the garden.

In general, seeds should be started 6-8 weeks before the date you want to transfer to the garden. Starting too early can easily lead to your seedlings becoming root-bound so if in doubt, wait a week or two. Please refer to UC Master Gardener Planting Calendar:

For ornamentals, pollinators and other non-edibles that can be started from seed indoors, refer to the seed packet for timing.

Seed Starting Basics


Use a blend specifically formulated for starting seeds. It should be light and uniform in texture, sterile and nutrient rich. Never use “native” garden soil and avoid regular potting soil. Make sure soil is evenly moist prior to seeding.


Just about any kind of container will work if it is clean and has drainage holes. “Clam shell” food containers, yogurt cups and other plastic packaging can be re-purposed along with nursery “six packs” and 4-inch pots. Wash, rinse and sterilize by spraying with a solution of 1 part chlorine bleach to 9 parts water and air dry before using. You can avoid containers altogether by using soil blocks. (See below for more information.) 


Fill your containers about 2/3 full of soil and follow seed packet directions for planting depth and spacing. Seeds that are started closer together will require “up-potting” and/or thinning at a later stage. Note: some plants, such as squash, don't like that kind of disruption and should stay in individual containers until transplanting time.


Moisture is essential for germination and watering is best done from the bottom to avoid dislodging newly planted seeds. Place seeded containers in a solid tray that will hold water. (Concrete and mortar mixing trays are ideal.) Add water to the bottom of the tray to a depth of approximately ½ inch. Seed containers should be checked frequently to make sure the soil is evenly moist but not wet or soggy. Adjust the amount of water added to the tray to maintain adequate moisture while avoiding standing water for more than a few hours. Clear plastic covers help to retain moisture as does a light topping of vermiculite.

Provide light and warmth

Find a spot with bright, indirect light such as a sunny window and where temperature is between 65 and 70 degrees during the daytime and 55-60 at night. If the perfect spot is not to be found, consider using grow lights and specially designed heating mats for plant propagation. Both are inexpensive and energy efficient.


Maintain proper moisture, light and warmth and in 6 to 21 days, seedlings will start to emerge. First to appear are the tiny green cotyledons that have burst forth from the seed. As soon as the true leaves appear, seedlings can be “up-potted” to larger containers.

“Hardening Off”

Young plants that have been grown indoors require gradual exposure to outdoor conditions. About two weeks before transplanting and when night time temperature has reached 50°, start the process by moving plants outside to a shaded location during the day and bringing them inside at night. After that, gradually increase the amount of sun exposure during the day and allow plants to remain outside at night.


When plants have been hardened off, it's time to plant! Prepare beds well ahead of time, then dig holes the size and depth of the seedling pot (deeper for tomatoes). Allow adequate spacing for the size of the mature plant. Invert the pot, allowing the seedling to pass through your fingers and gently grasp the root ball. Invert and set the plant into the hole. Gently tamp down, adding more soil if necessary. Water carefully and finish by adding a layer of mulch.

It's no wonder that seeds and the act of planting are the basis of so many sayings and inspirational words. Whatever seeds you decide to sow, you will be part of an amazing, eternal process of renewal.

Any questions?  Contact the Master Gardener Helpline:

For more on soil blocking:

For more on soil preparation:

Maggie Mah is a UC Master Gardener who is fascinated by seeds.

UC Master Gardeners of San Mateo-San Francisco County are volunteers who are trained under the auspices of the University of California to provide science-based information on plants, horticulture, soil and pest management at no charge to the public. For more information and to find out about classes and events in your area, visit our website where you can also sign up for our newsletter:

By Maggie Mah

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