Avoid These 12 Common Seed-Starting Mistakes
Although seed starting is not difficult, there are a few ways it can go wrong, impacting germination or killing your seedlings before you get a chance to transplant. Gardening expert Madison Moulton shares 12 common seed-starting mistakes you should avoid this season.
Contents
After a long winter, your green thumbs are probably twitching with excitement to get gardening. And one of the tasks we generally look forward to the most is seed starting. Despite how many years I’ve seen it happen, nursing a tiny seed into a mature and productive plant still seems like magic.
Unfortunately, there are often stumbling blocks on the way, especially if you’re sowing seeds for the first time. To ensure your garden thrives this season, avoid these 12 common seed-starting mistakes. We’ve all made them, but hopefully, these reminders will help you avoid them this time around.
Starting Seeds Too Early
When you’ve been cooped up all winter without much to do in the garden, seed starting seems like the light at the end of the tunnel. But don’t let your excitement get the better of you by starting seeds too early.
If you direct sow long before your last frost date, you may struggle to keep young seedlings alive in fluctuating temperatures. Even if you’re sowing indoors, early planting can leave your seedlings leggy and rootbound before it’s safe to transplant.
We can’t control the weather, and unfortunately, your seedlings are at its mercy. To avoid this seed-starting mistake, always plan according to the typical frost dates in your region. Rather than rushing, channel your enthusiasm into ordering seeds and gathering supplies for when the time is right. If you need a guide to how and when to sow indoors, we’ve got one here.
Starting Seeds Too Late
Although it’s not as detrimental as starting early, starting seeds too late can also be problematic. The reasons will depend on what you’re growing.
Some crops (spinach, for example) bolt quickly in the heat and can’t be sown too late in the season. Others need enough time to mature and fruit before temperatures drop again and kill them off in fall. Plant tomatoes too late, and you might only see green fruits before the first frost.
Pay close attention to the timing instructions on your seed packets. Count from your average last frost date (or first frost date, depending on what you’re growing) and time your sowing accordingly.
Not Reading Seed Packets
Seed packets aren’t just there to be ripped open immediately to reach the seeds they hold. On them, you’ll find details that tell you everything you need to know about sowing: the best time to plant, planting depth, days to maturity, and importantly, if your seeds need any special treatment (like stratification or scarification).
Ignoring these guidelines can leave you with much lower germination rates, weak plants, or the worst outcome, no plants at all. They’re added for a reason—follow them to give your seeds the strongest possible start.
Using the Wrong Soil
Soil should always be a consideration when gardening and that also applies to starting seeds. Some seeds can handle less-than-ideal soil, but many need that perfect environment to develop strong roots.
Chunky mixes with large particles (like some potting mixes) impact how much moisture seeds come into contact with and can stop small and fragile roots from anchoring into the soil. Dense clay-like soils prevent seedlings from pushing through the surface and can retain too much moisture, leading to rot. Using any soil from the garden can transfer weed seeds or soil-borne diseases to your new plants. In other words, this seed-starting mistake can have a lot of negative consequences.
Our recommended mixture is one part coconut coir, one part pumice or perlite, and one part compost. If you have worm castings on hand, mix them in up to half of the compost’s volume. You can also add a sprinkling of azomite for trace minerals. This fine-textured mixture helps seeds germinate quickly and grow as strong as possible.
Planting at the Wrong Depth
Pay attention to packet instructions for seed planting depth. Ignoring this can cause problems for young seedlings or inhibit germination completely.
If you bury seeds too deeply, they may not have enough energy to make it to the surface and reach the light source to continue growing. Plant them too shallow and they might dry out, get knocked around by water droplets, or be eaten by birds.
The general guideline is to plant seeds at about twice their largest dimension. But always double-check the seed packet or online for information. Small seeds typically need light to germinate and should be sprinkled on top of the soil or covered very lightly. Larger seeds can handle deeper planting, but be careful not to compress the soil too firmly on top.
Ignoring Light Requirements
The difference between scrawny seedlings and healthy ones is often the quality and duration of light they receive.
If you’re relying on a dim windowsill to grow strong seedlings in the middle of winter, you may be disappointed. Without sufficient light, seedling stems grow leggy and weak as they stretch toward whatever light they can find. This ultimately leads to floppy, vulnerable plants that struggle after transplanting or don’t even make it that far.
Grow lights are a must-have if you struggle with this seed-starting mistake. Set them up above your trays and they will provide strong overhead light to encourage the seedlings to grow upright.
Ignoring Temperature Requirements
Along with light, seeds also need the right temperatures to germinate, and even minor variations can make or break success. Soil temperature is the most important. For example, tomatoes, peppers, and other heat-lovers germinate best in soil kept around 70°F or higher. Others can manage in lower temperatures, but they still need some change in soil temperature to trigger growth.
If you’re sowing indoors, keep trays in a warm area of your home or use a seed-starting heat mat. If you’re winter sowing, you don’t have to worry as the seeds will germinate when the soil warms naturally. Either way, keep in mind that seeds won’t cooperate in cold soil, no matter how often you water them.
Overwatering
We seem to go on about overwatering, but that’s because it really is a common seed-starting mistake and one of the most damaging. Excess water can suffocate seeds and seedlings, leading to rot, fungal issues, or damping off.
It’s a common mistake, usually driven by worry that your seeds might dry out. But seeds need a balance of air and moisture to germinate. You may be killing them out of worry and love, but they end up the same way, no matter the intention.
When watering seeds, water gently or from the bottom, checking the soil before each watering session. If the top layer is still moist, they don’t need more watering.
Underwatering
The opposite mistake can be just as damaging. Seeds that dry out mid-germination often fail to recover, stopping growth entirely. If the seedling has already sprouted, inconsistent moisture leads to weak development and higher susceptibility to disease. No matter which stage you’re at, watering is the most important maintenance task to keep track of.
Check on your trays daily. If you notice the soil surface is dry or has pulled away from the edges, it’s time to water. The soil should be lightly moist, not soggy, but not too dry either.
Overcrowding
Sowing many seeds in a small area is another common seed-starting mistake, especially when direct sowing outdoors. You may be trying to maximize limited space, or boost your germination rates to make sure the bed is filled with no gaps.
This doesn’t look like a problem when it’s just seeds below the soil line. But once they start to grow, overcrowding quickly becomes an issue, leading to competition for light, nutrients, and space. Lack of airflow also creates the ideal conditions for fungal disease to settle in.
Follow spacing recommendations on the seed packet, or sow only a couple of seeds per cell if you’re using trays. Overcrowding might look lush initially, but it results in leggy growth and weaker plants overall.
Not Thinning
When sowing in trays, we generally recommend sowing more than one seed per cell to increase the germination rate. But many forget one crucial step down the line: thinning. If all seeds germinate, you’ll have a crowded tray that chokes out any further root development. Overcrowded seedlings may also tangle their roots, complicating the transplanting process.
Once the seedlings are a few inches tall, remove the weaker of the two per cell, leaving only the healthiest. It may be hard to pick them out, but thinning ensures the remaining plants have the best possible start.
Not Hardening Off
After all your effort to grow healthy seedlings indoors, tossing them directly outside to face the elements is a surefire way to shock them. They’ve known only controlled temperatures, low wind, and consistent lighting, so they need time to adjust to adjust to outdoor environments before transplanting. This process is called hardening off, and skipping it is a damaging seed-starting mistake you don’t want to make.
A week or two before you plan to transplant, place your trays outside in a sheltered spot for just a couple of hours a day, gradually increasing the time. By the end, your seedlings will handle full outdoor exposure much more effectively after they go in the ground.
