5 Seed Starting Mistakes to Avoid for a Thriving Spring Garden

Gardener making mistake of overwatering seed trays during seeding season

Before you start throwing seeds into the soil, it’s vital to understand what it takes to nourish a tiny seed into a strong plant. Your garden’s success heavily depends on the initial spring sowings that set the stage for crop health and vigor.

Mistakes in the seeding process can cost you significant amounts of money and time due to poor germination, weak seedling growth, and even crop failure.

After sowing millions of seeds during my 8-year organic farming career, I’ve gathered some industry-tested seeding tricks that will maximize your germination and help you grow stronger plants. Set yourself up for a thriving garden season by avoiding these common seed-starting mistakes and learning what to do instead!

Common Seed Starting Mistakes

Gardener making mistake of overwatering seed trays during seeding season
There are a number of seed starting mistakes gardeners unknowingly make each season.

If you’re tired of sick baby plants or seeds that never come up from the soil, it may be time to level up your seeding techniques.

Whether you are starting seeds indoors or sowing directly in the garden, many vegetable seeds fail because of issues with seed depth, irrigation, timing, and soil type. Use these science-backed tips to get the most out of your seed packets every time. 

Mistake #1: Planting Seeds Too Deep

Gardener planting seeds on top of a small garden carton. She is planting into an egg carton and pulling soil seed mix from a bowl. Nearby is another small set of containers with tabs used for marking each seed.
Planting seeds too deeply can impact germination rates.

When you sow a seed too deep in the soil, the seed does not have enough energy to grow upwards to the light. As a result, many deeply-sown seedlings end up dying or rotting in the darkness of the soil before they can germinate. From the gardener’s perspective, this looks like empty seed-starting trays or barren beds. 

This mistake is most common with small-seeded vegetable crops, such as:

  • Celery
  • Lettuce
  • Basil
  • Tomato
  • Arugula
  • Brassicas (cabbage, broccoli, kale, etc.)
  • Fennel
  • Oregano
  • Thyme

Seeds must be buried at a specific depth based on the size of the seed. With hundreds of different seed shapes and sizes, not all seeds are created equal. A big bean seed can tolerate up to an inch of soil over it, while a tiny lettuce seed needs to be sown just below the soil surface.

How to Avoid It

Before you shovel loads of soil over your seeds, make sure you know what depth the seed needs to be planted at for optimal germination. Remember this seeding rule of thumb, and you will never make a seed depth mistake again: 

Seeds should be planted twice as deep as their largest dimension.

In other words, you should never plant a seed any deeper than twice its diameter. The sowing depth is directly proportionate to the size of the seed. Fortunately, you do not need a magnifying glass and a tiny ruler to figure this out. A “guestimate” will do as long as you make your seeding hole shallow enough that the backfill soil won’t bury the seed. 

A seed only has so much energy stored inside of it. This energy is designed to fuel the seed through the germination process until it reaches the soil surface, grows, leaves, and can start photosynthesizing for itself. 

The endosperm is the part of a seed where starchy food reserves are held. A large seed like a pumpkin or cucumber seed has a lot of endosperms, which is why the seed is so big.

These big seeds can be planted up to 1” deep because they have a lot of food to nourish the seedling on its journey up to the soil surface. However, a tiny basil seed needs to be sown shallowly (about ¼” deep) because it doesn’t have much food (endosperm) to support it before it starts photosynthesizing. 

Seed depth is not rocket science, but it may require a little practice. Experiment with different sowing depths in the same seed-starting tray or garden plot, and keep notes in your garden journal.

If you notice that your basil seedlings are much stronger when they are barely dusted with a layer of vermiculite, take note of that discovery and use it every time you seed basil!

Mistake #2: Underwatering or Overwatering 

Gardener watering a seed tray with a spray bottle. The seed tray is a turquoise color, and sits in a plastic container.
Too much or too little water will impact germination rates.

Seeds are like helpless babies that need a constant supply of moisture until they grow mature roots. If you let your seed trays or garden soil dry out, it could halt your entire garden season for that crop.

Too little water can quickly kill a newly germinated seedling because a lack of moisture halts the baby plant’s growth.

On the other hand, overwatering can drown a seed, leading to rotten seeds or seedling diseases like damping off. Saturated, soggy soil creates what’s called a “hypoxic” root zone. This means there isn’t enough oxygen for the seedling roots to breathe properly. 

Both underwatering and overwatering are major mistakes that can leave you frustrated and confused. Instead of relying on inconsistent rainfall or automated watering systems, we recommend checking your seeds every day and recognizing signs of improper soil moisture.

Underwatered SeedlingPerfectly Watered SeedlingOverwatered Seedling
Soil appears cracked, dusty, or pale Soil appears loamy, rich, crumbly, and darkSoil looks soggy, mushy, and may have a green algae growth on the surface
Wilted seedlings, often with brown leavesUpright, strong plant with fleshy bright green leavesWilted or droopy seedlings, often with yellow leaves
Poor germination (seed never emerges) or weak growthRobust, disease-free growth with plenty of airflow above and below-groundWeak stems prone to damping off disease (a fungal disease that creates a shoestring stem and/or fluffy mold at the seedling base)

Finding the perfect balance of water for your seedlings will revolutionize your seed-starting efforts by improving germination rates and preventing diseases.

How to Avoid It

Check on your baby seeds at least once per day! And always check the soil moisture before watering seedlings! You can use these three cues to ensure that you know whether it’s time to water or wait:

Seedling Appearance

Wilted seedlings with yellowing leaves are a bit confusing because they could signal underwatering or overwatering.

If your baby plants look droopy, inspect them closer. An underwatered seedling may look shriveled or slightly brown, while an overwatered seedling tends to look weighed down by the water and may have soaked blister spots on the leaves. 

Soil Feel

Get your hands dirty! You should always touch the soil before you water. For large containers or garden beds, stick your finger an inch or two deep into the soil. For small cell trays, touch or scratch the soil surface to avoid dislodging the seedling.

If your skin comes out completely clean, the soil is probably too dry. If some soil sticks to your skin and feels moist, you may not need to water. If the soil sticks to your skin like brownie batter, it is likely too wet.

Soil Appearance

Overly dry soil usually appears cracked and brittle. Depending on your soil mix, it may have a dusty, dull, and/or gray appearance. Perfectly moist soil looks rich, brown, and fluffy. Overly wet soil tends to look super dark in color and may have green algae growing on the surface.

When growing in cell trays or containers, it always helps to lift the pot up and check the drainage hole as well. Sometimes the soil surface can look wet, but water hasn’t actually penetrated the lower soil layers. Watch for the following signs.

Dusty Grey SoilIf the soil looks dusty and grey or is falling out of the hole, you probably need to do a deeper watering until moisture pours out of the drainage hole.
Roots Climbing Outside Seed TrayIf roots are climbing out of the hole, the plant may be scavenging for water. This could also be a sign that your seedling is rootbound (overgrowing its container) and needs to be up-potted.
Water Dripping From DrainageIf water is dripping out of the drainage hole or the bottom of the container has a stinky smell, you are likely overwatering, and the seedling needs to dry out.

Once you’ve determined that a seed needs water, ensure you are watering properly:

  • Use a fan-shaped hose nozzle to distribute water lightly and evenly.
  • Never blast water in one specific location.
  • Heavy spurts of water can dislodge seedings.
  • Keep the hose moving to avoid drowning one area of soil.
  • Irrigate seedling containers until water pours out from the drainage hole, then stop.

Naturally, there is no “one size fits all” approach to watering garden seeds. You will have to adjust your watering regimen based on the soil type, crop type, seedling age, humidity level, and temperature.

Observation and experimentation are key!  Bottom watering can help your seeds if you are struggling with too much moisture.

Mistake #3: Seeding at the Wrong Time

Gardener making seed starting mistakes with seeds in garden
Seeding at the right time for your climate is critical.

When it comes to the seeding, timing is everything! Some gardeners get overly eager in the spring and sow their seeds too early. 

Seeding too early can cause:

  • Premature plant death: Direct sowing too early in the spring can cause some major disappointments if the weather doesn’t cooperate and a late spring frost wipes out your tender plants.
  • Leggy, rootbound seedlings: If you sow seeds indoors too early in the spring, they may outgrow their containers before it’s time to transplant. This can delay the plant’s establishment in the garden and lead to weak vigor or stunting.

Other gardeners may forget to seed until later in the season. They could potentially miss their opportunity to establish strong crops before summer.

Seeding too late can lead to:

  • Insufficient frost-free days: Warm-weather crops like peppers, tomatoes, and eggplants need a certain day length to properly flower and fruit. Late plantings are especially problematic in northern zones where the summer weather only lasts for a brief window.
  • Improper weather conditions: For example, peas and spinach love the chill of spring. If you plant them too late, they may bolt before you can get an adequate harvest.
  • A short harvest window: For example, late-planted tomatoes may have little to no yield before fall frosts approach. Even worse, late-sown winter squash may need to mature properly and cure in time for cold, wet autumns.

How to Avoid It

Time your seedings based on the days to maturity listed with the seed variety. Pay close attention to growing guides or packet instructions, and always plan your seeding on a calendar ahead of time! Mark every seeding with a popsicle stick that lists the sowing date and crop variety.

Keep track of your seeding dates in a garden journal so you know what works and what doesn’t work. If you seeded your tomatoes on March 1 last year and they were leggy or overgrowing their containers by the time you transplanted in early May, this information can be incredibly useful for proper timing this year. 

Seeding too early is easily remedied by sowing another succession. Succession planting of some crops every 2-4 weeks acts as a buffer against seeding failures. For example, if one planting of “teenager” lettuce fails, you have another one lined up. 

However, late seeding usually means you should purchase established plants from your local nursery or garden store. Cut your losses and get strong seedlings in the ground rather than waiting for another round of seeds. This is especially important for long-season crops like peppers, tomatoes, onions, melons, and winter squash.

Generally, crops like tomatoes and squash are best sown 4-6 weeks before the expected last frost date. Seeding them too early can lead to leggy, rootbound starts in your nursery, or frost-damaged plants out in the garden. 

Mistake #4: Seeding Too Densely 

Gardener seeding seeds in small plastic tray. There are several different small seed containers with seeds resting atop the dense soil. All of the small seed containers are contained in one larger plastic tray.
Sowing seeds too densely can lead to stunted growth.

Just like people crammed together on an overcrowded subway, plants will become upset by insufficient spacing! It’s normal for beginner gardeners to think that extra seeds mean extra yields. However, dense seeding can actually reduce your harvest size!

For example, if you plant 20 broccoli seeds with just 4” of space between them, you may end up with just one or two tiny broccoli heads. Because the plants are practically growing on top of each other, no single plant has enough resources to reach its full potential.

On the other hand, you could sow just 5 broccoli seeds 12” apart; you could harvest four to five big, healthy broccoli heads. Generally, fewer seeds that are properly spaced are more successful than lots of seeds planted too close together. 

Other signs of overseeding include:

  • Huge clumps of seedlings in one small space
  • Leggy, weak stem growth as seedlings try to reach up and beat out their neighbors
  • Competition for water and sunlight
  • Damping off or powdery mildew (fungal diseases) due to insufficient airflow between plants

How to Avoid It

Check the seed spacing before sowing seeds. Generally, you should only plant 1-2 seeds per cell in indoor trays. Use a hand seed sower to help single out smaller seeds and tap them into place.

Seeding at the proper spacing will save you seeds and time, but if you accidentally drop too many seeds in the soil, no worries! As long as you thin them, your seedlings can still thrive. The best time to thin is when seedlings have started growing their first true leaves. 

When thinning, remember to:

  • Keep the strongest plants and remove the rest.
  • Use needle-nose shears or scissors to cut the weaker seedlings at the base. 
  • Avoid pulling or yanking unwanted seedlings out because this can disrupt the roots of the remaining plants.

Mistake #5: Using the Wrong Seed Starting Mix

Seed starting mix indoor garden with seeds atop the container. Small cherry tomato seeds are fresh plantings in a cardboard seed starting tray with moist, dark soil.
Ensuring you have a proper seed starting mix will help facilitate proper germination.

A seed is only as strong as its environment! It’s difficult to thrive in a setting that makes it hard to breathe or drink water. Many gardeners neglect to consider the seed-starting medium. A spinach seed tossed into a heavy clay soil will have a much harder life than one planted in a loamy, rich seedling blend.

While some robust garden plants, grasses, and wildflowers can tolerate being tossed into any soil (we see you, dandelions!), vegetables and fruits tend to be more finicky about their preferences. No matter what seeds you are starting, take the time to research and prepare the optimal soil environment before you plant! 

How to Avoid It

If you are starting seeds indoors, the most important thing to invest in is the seed starter mix. Always select a high-quality, well-drained soil blend that is specifically labeled for seed-starting. Don’t use potting soil, garden soil, clay, or dirt from outdoors. You can also make your own seed starting mix if you can’t find one that fits your needs.

Look for ingredients that ensure proper drainage and nutritional support for your seedlings, including:

  • Perlite
  • Vermiculite
  • Compost
  • Vermicast
  • Peat moss
  • Coco coir

If you are direct sowing, be sure to properly prepare your seed bed based on the crop’s needs. For most vegetables, this sequence of garden bed preparation will set you up for success:

  1. Weed the bed
  2. Use a shovel or garden fork to mix in high-quality compost
  3. Broadfork or loosen the lower soil layers (especially if it is heavy clay)
  4. Rake the surface flat before seeding

If you are struggling to put together all the materials you need for a hospitable growing environment, you can also look for pre-planned seed starting kits with everything you need to get started.

Final Thoughts

It’s normal to make mistakes as a beginner gardener. Those mistakes are what help you learn and improve your growing methods every season! 

Fortunately, starting seeds doesn’t need to be a gamble. Ensure greater chances of seed success by narrowing down these five simple factors:

  1. Depth: Sow seeds twice as deep as their largest dimension.
  2. Moisture: Avoid underwatering or overwatering.
  3. Timing: Plant your seeds based on days to maturity and frost dates.
  4. Spacing: Don’t plant seeds densely and thin seedlings.
  5. Soil: Prepare the seed-starting environment with well-drained soil.
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