Starting Seeds Indoors

starting seeds indoors

Starting seeds indoors

When starting seeds indoors, consider varieties such as tomatoes, peppers, onions, perennials, and some annual flowers. These crops can really benefit from an early start indoors, especially if you live in an area that has short warm seasons.  Starting seeds indoors is particularly helpful for individuals that are starting their gardens in Southern California, or in other areas of high elevations or in zones outside of nine and ten. 

Here are our tips if you are going to start your seeds indoors.


Providing adequate light is the most important step in growing healthy seedlings. Long, tall, skinny seedlings that tend to fall over are usually the result of not enough light. To help the seedlings get enough light, you can use fluorescent light(s), preferably a 4-tube ballast. The lights must be placed 1” – 2’ above the seedlings, and can be hung on chains, and hooked into ceiling hooks for easy adjustment as seedlings grow. Seedlings should receive at least 16 hours of light per day.

Seed Starting Soil

Purchase a high-quality seed starting mix that holds moisture and that has good drainage. As a result of using an appropriate seed starting mix, you will substantially increase your success rate.


Soil must be kept moist, but not soggy. If the soil becomes completely dry, the seedling(s) will likely die. On the other hand, if the seedlings become too soggy, it could result in disease problems for the seeds or seedlings. When seeds become too soggy, it is common to notice mold forming on the soil, which can be detrimental to the plant. 

What to plant in

Seed starting trays and larger pots for transplanting seedlings are available. However, almost any container can easily be used to start seeds, such as milk or egg cartons. First, find the container that works best for you. Second, punch holes in the bottoms, to ensure adequate drainage. After that, be sure to keep the soil moist, until seed germinates. A good way to  do this is to cover the container(s) with a clear lid or clear plastic wrap. Once you start to see the seedlings start to emerge, you will need to remove the cover.

If your containers are very small, and it’s not yet time to plant your seedling outside, you may need to transfer them to larger containers to allow for proper growth. First, choose a container twice the size of the original one. Next, fill it part-way with moistened potting soil. After that, carefully transplant the seedlings, handling them by the root ball or by the base of the stern. Then, add the soil to fill. Lastly, water gently.

Why you should harden off your seedlings

When starting seeds indoors, it may take some time for them to adjust to the new conditions of outdoor living. This is why it is important to harden off the seedlings. It is best to harden off the seedling for about a week. To do this, take the containers outside and place them in a filtered sun/shade location away from harsh winds during the day. Gradually increase time outdoors. This process is very important for the plant to acclimate from the conditions inside to the new outside conditions. Most importantly, do not place your seedling in a high wind area, or on hot concrete. Be sure to check your seedlings often.

When to sow seeds

San Diego Seed Company packets indicate the optimum sowing time based on the average last spring frost date. As for Zones 9 and 10, you can look for information on what season to grow your plants in. Warm-season (May-Oct) and cool season (Nov-April).


Generally, tomatoes are sown indoors 6-8 weeks before the average last frost, peppers 8-10 weeks, onions 8-12 weeks. Flower seed sowing time can vary from 4-12 weeks before the average last frost depending on the variety.  


Warm-season crops such as beans, cucumbers, melons, pumpkins, squash, and watermelons are frost-sensitive and should be sown after the average last day of frost in your region. Cool-season crops such as carrots, lettuce, peas, radish, chard, and many leafy greens can be sown as early as 6 weeks before the average last frost for spring harvest, and in late summer for a fall crop. Most annual flower seeds are sown around the average last frost date even though some can be earlier. Perennial flower seeds can be sown almost any time – early spring through late summer. Even a late fall sowing works – seeds remain dormant in the ground until conditions in early spring permit the seeds to germinate.

When is your average last frost?

Knowing the average last day of frost in your region is crucial when planting a garden, and being an expert grower. Find out your last day of frost, by calling your county Cooperative Extension Service. Similarly, you can consult websites like:

Perennial vs. annual

A perennial is a variety that regrows from the root system every year.  In contrast, annuals do not regrow from their roots every year. However, there is a possibility that annuals produce seed that will germinate and grow the following year.

The advantage of perennial is that it doesn’t need to be replanted every year; a disadvantage is that perennials have a shorter bloom period than most annuals. When choosing perennials for your garden, mix varieties with different bloom periods so that you have color in your garden over a longer period of time. 

Annuals usually bloom for a longer time period than perennials – in many cases, they bloom most of the growing season (spring to late fall).

Common Challenges when Starting Seeds Indoors- and our Solutions

Getting the best seed germination

Occasionally, seeds may fail to germinate. Common reasons include:

 – Sowing the seeds too early. For example, when the soil temperatures haven’t warmed up enough.

–  Not sowing the seeds at the recommended depths. For instance, sowing them too deep or too sallow.

– Seeds are not kept consistently moist. As a result, the seeds dry out. 

– Unusually cool or wet weather occurs. 

Build better garden soil

Adding organic matter, such as compost or manure, to your garden soil will help create healthy soil. Don’t over-fertilize your vegetable garden. But do make sure you feed your vegetables. Refer to the fertilizer instructions to avoid over fertilization.

Space your plants correctly!

Spacing between plants is important for proper development. Proper spacing allows for adequate sunlight, air circulation and room for roots to grow without competition.

Monitor for diseases

Many plant diseases can be prevented by starting with high-quality fresh seeds and good gardening practices. This includes good garden hygiene like removing diseased plant material from the garden.

Prevent and monitor for pests

Pest information can be found on the UC IPM website in great detail.

Give adequate sunlight

Most vegetable plants need at least 8 hours of direct sunlight. Some root crops (carrots, beets) and leaf crops (lettuce, kale) can manage with 6 hours of direct sun. If plants are not grown in optimal conditions, it is likely they will have pest and disease issues. 

Control weeds

Weeds compete with seedlings and other desirable plants for water, light, and nutrients.  In addition, they can harbor harmful insects and diseases. Keep flower and vegetable beds weeded all season, particularly during initial seedling emergence. 

Retain Moisture

Mulch is a layer of almost anything – grass clippings, leaves, bark, newspaper – placed on the surface of the soil in order to maintain even soil moisture and prevent weeds from coming up. Mulching is critical in dry regions, particularly in zones 9 and 10. When using mulch it is recommended to be applied thickly, several inches if possible. As a result of a thick layer of mulch, weed seedlings will be less likely to emerge. When using leaves and wood mulch, these items break down and improve the soil over time while keeping moisture in the soil. 

Once you have mastered a few of the basic steps of seed gardening you will realize the potential you have to create a beautiful and bountiful garden with local, organic seeds!

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