Seed Starting Mistakes to Avoid

Estimated reading time: 8 minutes

Starting plants from seeds indoors is a great way to save money and extend your growing season. It also is a fun and gratifying project the whole family can enjoy.

However, each type of plant has its own particular needs for seed-starting. By not meeting these needs or making some other common mistakes, you can derail the whole process. Fortunately, most of these errors can be avoided with a bit of preparation and know-how.

Your first step is to read and carefully follow your seed packets’ instructions. You’ll find a wealth of information, including planting depth, spacing, light, moisture, soil, and optimal timing for sowing. These details typically are the ones that make the difference between a healthy plant and one that never gets off to a good start.

This article offers an overview of nine seed-starting mistakes to avoid.

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1. Bad timing

Whether you’re starting seeds indoors or outdoors, timing is everything. If you start seeds indoors too early, you may have seedlings that are ready for planting when it is too cold outside. Yet, if you start too late, you may not be prepared for optimal spring planting time.

For correct timing, check the last average frost date for your area here, or you can ask your local cooperative extension service. Then, check the seed packet. For example, it may say, “Start seeds six to eight weeks before the last frost date.” Use that information to calculate your optimal seed starting time.

Most plants are ready to move outdoors in four to six weeks, weather permitting. But you’ll also want to consult the USDA Hardiness Zone Map for more information. 

2. Wrong planting depth

Another common mistake is planting your seeds at the wrong depth. Some seeds need complete darkness (more depth) in order to germinate, while others need some light (less depth).

Once again, you can check the back of your seed packet for this important information and other growing tips.

3. Less-than-ideal soil

Planting seeds in the wrong soil can affect germination. For example, if you use your garden soil, you could introduce pests or disease to the seed-starting process. On the other hand, some commercially-sold potting soil is too dense for tender seeds.

Your best bet is to use light, fluffy soil (like this one) that is intended for seed-starting. However, keep in mind that this type of soil will not continue to provide the nutrients your seedlings will need after transplanting. (Read on for more on fertilizing.)

4. Not enough warmth

For this tip, we’re talking about soil temperature, not air temperature. Most seeds require a soil temperature of 70 to 80°F in order to sprout. Exceptions are onions, lettuce, and peas, which prefer a 50 to 60°F range.

 You can help keep seeds warm by covering the containers. Another option is to use a seedling heat mat.

5. Lack of light

Most healthy seedlings require 14 to 16 hours of light – much more light than even a sunny windowsill can provide on short winter days. When seedlings don’t get enough light, they typically grow tall and lanky – or leggy. These seedlings tend to be weak and top-heavy.

The answer to this problem is to provide stronger and longer supplemental light. Many options are available online (like this one) and in your local garden center. 

6. Too much or too little water

Most seeds like things moist but not too wet. Maintaining that balance can be challenging. 

Here are some tips:

• Moisten the potting soil before adding it to your containers.
• Before the seeds sprout, cover the tray with a humidity dome or other plastic lid.
• Mist the top of the soil with a spray bottle.
• After the seeds sprout, add water to the tray from below rather than pouring or spraying water from above. This process encourages root growth.
• Develop a consistent watering schedule, choosing to err on the lighter side when in doubt.

Another potential problem with watering your seedlings is the water itself. If you notice a hard crust on the surface of your soil, you may have hard water in your home.

“Hard” water has a high concentration of dissolved calcium and magnesium. This mix results in soil with a high pH and high alkalinity. Rainwater tends to balance out the effect of hard water outdoors, but you may need to switch to distilled water for the health of your indoor seedlings.

Here is more information on watering seedlings. 

7. Fertilizing problems

The seed itself contains all the nutrients a seedling needs for a few weeks after it sprouts. Adding fertilizer at this point is not only unnecessary, but it could be harmful. However, after a few weeks, young seedlings will need more nutrients than their potting medium can provide.

After seedlings have their first set of true leaves and are about two inches in height, consider adding a fertilizer that contains an even balance of nitrogen, phosphorous, and potassium. Here’s more information on how and when to fertilize seedlings.

8. Crowding issues

The more, the merrier is not true for seedlings. When not thinned, new sprouts compete with each other for water, light, root space, and soil nutrients. Crowded seedlings are more susceptible to disease and stunted growth.

Some gardeners simply like to pluck out excess sprouts. Others trim excess sprouts with pruning snips to help determine the healthiest and most vigorous plants. You also can gently remove a cluster of sprouts and replant them in another container.

9. Not hardening off seedlings

Seedlings started in a sheltered environment must be prepared for spending time outdoors. The process of gradually introducing them to outdoor conditions is called “hardening off.”

You begin the process by bringing the containers outside on a mild day for a few hours in a shady spot. Slowly increase the amount of sun exposure and the time outside each day over a week’s time. Here is a guide for hardening off seedlings.

If you have specific questions on seed starting in your area, we recommend you consult your local Master Gardeners or extension service. An excellent resource for beginners is The New Seed-Starters Handbook by Nancy Bubel and Jean Nick.

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