Green Garden Dreams

The Joy of San Diego Vegetable Gardening

Starting Vegetables From Seed


Starting vegetables, or any plant, from seed is a joy and a wonder. Watching plants grow from seed is amazing and fun. To take this tiny dry little bit of matter (and every kind of seed is a different shape and color), give it water and soil, and watch new green life emerge from it, is truly a beautiful thing (click to enlarge)*:

Beans Emerging in Morning Sun 07/24/'11
Royalty Purple Pod Beans Emerging in Morning Sun 07/24/'11

You can also save a lot of money by starting your own plants from seed.

What Every Plant Needs

Most people know that plants need light, water, nutrients and air. But many people don’t know that roots breathe, and need lots of air (oxygen, carbon dioxide, nitrogen) to live and grow. This is also true for seeds and seedlings – perhaps more so.

This fact became very clear to me when I grew vegetables and herbs hydroponically (“soilless gardening”) in a very loose volcanic rock, and saw how quickly and vigorously plants grew. I was also using a “fill and drain” method which pulls air down into the root zone as the nutrient solution drains out of the bed.

Professional growers and advanced hobbyist growers sometime use a propagation method for cuttings called aeroponics, that is specifically designed to provide high levels of oxygen to the root zone. (Also see “How does Aeroponics Work and How to Set Up a Aeroponic System” at Happy DIY Home)

What Kinds of Vegetables are Good to Start from Seed (in Pots or Indoors) and Transplant to the Garden?

The short answer is, types that have small seeds and take a longer time to get started, or need an early start. You can grow them in small pots like peat pots or 6-packs and set them out. It’s useful to plant them in pots such as peat pots (which can be put directly in the ground) if you want an early start on the season or want to baby them to maximum health (the right amounts of water, light, temperature, etc.)
Examples include tomatoes, peppers, broccoli, and herbs.

What Kinds of Vegetables are Not Good to Start from Seed and Transplant?

The short answer is, types that are sensitive to being transplanted, or have large seeds and grow quickly.
Examples of root-sensitive vegetable plants are radishes and corn. Radishes have very long and delicate root hairs that are easily damaged. Root hairs are the super fine, single cell roots that grow from the main root, and that absorb water and nutrients from the soil. If they are disturbed or damaged, the plant cannot absorb water and nutrients and will suffer or die.

Root Hairs of a Radish Sprout
Root Hairs of a Radish Sprout


It’s best that a vegetable plant be allowed to grow quickly and continuously, without any major “stops” to it’s growth.

Vegetables with large seeds like beans and squash are better planted directly in the garden where they can grow without stops to their growth. There’s usually no reason to start them early indoors in Southern California. They can be grown in pots before being transplanted, but they need to be large seed-starting pots to give the large vigorous roots room to expand. However it’s better to plant them directly in the ground, unless they need a head start (because of the season).
Beans are of tropical origin and need the soil to be warm, or the seed will rot in the soil (it’s happened to me), especially if it’s soil with a lot of clay. Clay holds a lot of water and has extremely small particle size, so does now allow the soil to “breathe” as well as a coarser soil.

What Containers To Plant Seeds In

Clean containers and sterile soil. Fungus is the enemy of seeds and sprouts. Peat pots are an excellent choice because they can be planted directly in the ground and minimize transplant shock (it’s still best to use some B1 though, and there will probably be roots sticking out from the sides and bottom of the pot). Make sure they are new peat pots, or sterilize old ones with boiling water.

How Deep to Plant Seeds?

About 3 times the width of the seed is a general guideline that you will hear a lot. So very fine herb seeds for instance, need to be quite close to the surface. If you were to plant mint seeds for instance, which are extremely small, you would merely sprinkle them on the surface of the soil, then sprinkle some sterile, sifted seed starting mix over them, or perlite & vermiculite -just enough to barely cover them.

If a large seed is too close to the surface, the roots will not be able to get a purchase within the soil, be too exposed, and the young stem and seed head will not get established deep enough. A seed planted too deep will either not be able to reach the surface, or expend too much energy getting there.

Seed packets will tell you on the back how deep to plant the seeds, and how far apart to plants them, as well as how far apart they should be thinned to once they start growing. You can also find guides online, like here.


Keep seeds damp, but be careful not to wash them away or disturb the soil. One way to do this is to water from the bottom, so the water is wicked up. You can also use a fine spray or small stream of water, or water from the side. Seeds and sprouts (and all plants for that matter) need air as well as water in the root zone, or they can’t breathe. Also, fungi are more prone to grow on a seed if it’s wet but without enough air. Therefore be careful not to overwater, and use soil that is loose, such as with lots of organic matter, perlite,¬† (in the case of potting soil), and not compacted. Of course, you definitely do not want them to dry out – that would be the end of your delicate sprouts – so it’s a balance between air, water, soil, temperature, and light (radiation) intensity.

Light and Temperature

It’s very important that seedlings have enough light, and the right kind of light, so they are strong, and don’t get spindly (technically known as etiolated). Put them in a South-facing window (careful if they are under a plastic dome or wrap as they can overheat) or under lights if they are indoors. Use fluorescent, not incandescent. Fluorescent lights and LED plant lights have the proper light frequencies. Incandescent lights have too much red and infrared light and plants will get spindly. They need to be close to the fluorescent lights, roughly between 8 and 16 inches. But not too close or they will get burned.

Seeds need some warmth to sprout. Different seeds have different temperature requirements. Plants of more tropical origin like more warmth. Some examples are tomatoes, peppers and beans. You can use an electric seed warming mat if the temperature of your room or greenhouse is too cold. Sometimes the mat can make it too warm so you might want to use a book or stack of newspapers between the warming mat and the bottom of your seedling tray for insulation.


Use very dilute fertilizer after the first true leaves appear. The seeds leaves (or seed, in the case of such plants as corn and Scarlet Runner Beans) have stored food in them.


The important things to remember about transplanting are to lessen the shock for the plant, and increase it’s chance for a large and healthy spurt of growth into full vegetable-hood. When you move a plant from where it was growing, several things can potentially change: the light conditions (strength and color), the humidity, the temperature, the daylength, and possibly the chemistry of the soil and watering conditions.

For example, if you move a plant from growing indoors under fluorescent lights, to outdoors under full sunlight, that is a major change for the little plant-ling. You might want to give it a little shade, like some shade cloth or screen, or whatever you have, until it adjusts.

In some parts of the country, plants are started indoors until the weather warms up, to get a jump on the growing season. Once they are put out into the garden, they can be given help to adjust. Almost anything that allows light and air in but gives the plant some insulation at night will work. Examples include a 5-gallon water bottle with the bottom cut off

To help the roots adapt to their new soil environment, and lessen “transplant shock”, many people recommend using vitamin B1 (the kind for plants, gotten from nurseries).


Although it may seem obvious, sometimes the obvious needs to be stated. Plants need to room to grow, and if the roots and leaves are too crowded, too close to other plants, the plant “knows” this. It’s important to the plant because there is limited water and nutrients in a given area of soil, and limited air and sunlight in a given patch of earth.

It’s better to have fewer, healthier plants, than more, crowded plants. Plants that are crowded tend to be less healthy and therefore more prone to pests, and not living up to their genetic potential and will produce smaller fruits, seeds, roots, or whatever you are aiming to harvest. They won’t look¬† as nice too.

Thinning spacing is given on the seed packets. If you don’t have a packet, look it up, or just imagine how large the plants will be as they grow. You can always thin then more later, so don’t overdo it (like a haircut – you can always cut more but it’s hard to put hair back on!). That being said, it’s better to give a plant more space earlier – space to spread it’s wings as it were – than to wait.

* Here’s the same sprouts from the beginning of the article in the evening of the same day:

Beans Emerging Evening 7/24/'11
Royalty Purple Pod Beans Emerging Evening 7/24/'11

Here’s where I planted them – next to the corn so it can grow up the corn, as the corn grows (corn, beans, squash: the “Three Sisters” in Native American Gardening). Can you see the bean seeds in their little hollows in the earth, waiting to be covered with some soil? (I love the colors in the corn leaves in this shot):

Bean Seeds Next to Corn  7/19/'11
Bean Seeds Next to Corn 7/19/'11

Some Links

Starting Seeds Indoors-Is it worth it?

Planting Vegetable Seeds (University of California / Alameda County Master Gardeners)

How does Aeroponics Work and How to Set Up a Aeroponic System

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