| Written By Lara Wadsworth |
Thousands of people every year flock to garden centers nationwide to buy young seedling plugs. While it is incredibly convenient to buy seedlings ready to be planted in the garden, starting seeds at home has some significant advantages. Firstly, it is much cheaper in the long run. Even if you have to buy all the seed starting supplies along with the seeds, over just a couple of years, you will save money versus purchasing prestarted seedlings each year.
Secondly, it lets you be particular about the varieties you are growing. If you go to a garden center, they might have a couple of varieties of each plant but often skip plant groups altogether or leave out delicious, hardy varieties that would do well in your garden. On sites like True Leaf Market, you can browse thousands of seed varieties and even take a quiz to find the perfect ones for your growing location. However, many people are intimidated by starting seeds at home. I’m here to remind you that it all comes down to a simple formula. So, let’s talk about it!
This really comes down to the weather outside and what the seeds need. For simplicity’s sake, I will generally divide all garden seeds into two categories: cold start and warm start seeds. Cold-start seeds are the ones that can handle or even prefer cool temperatures in germination. Warm-start seeds are annuals that need warm, tropical-like conditions and will die at any hint of frost. If you live in zones 9-11, you don’t need to start seeds indoors because you have a long enough warm growing season for the plants to do well outdoors. However, you may still choose to do so for the benefits of a controlled environment. For zones eight or lower, the following is an uncomprehensive list:
Seeds to start inside ahead of time: tomatoes, peppers, melons, most flowers, warm-season vegetables.
Seeds to start outside when the weather has warmed enough: carrots, wildflowers, corn, cover crops, onions, kale, spinach, cool-season, and spring vegetables.
The perfect environment for starting seeds comes down to five factors: growing medium, heat, moisture, time, and light. If you can get these factors right and you get your seeds from a high-quality source, there is no reason why they won’t germinate.
The growing medium, in my opinion, has the most flexibility out of all of these factors. What you need to know is that the medium needs to be able to retain a good amount of water and be clean (sterile if possible). If you use outdoor soil (not clean) or pure sand (can’t retain water), you will have a hard time germinating and growing seedlings. Using a second-hand growing medium dramatically increases the likelihood of your seeds rotting or your young seedlings getting various diseases such as phytophthora. My favorite is pure coconut coir, but fine-grain potting soil or blends containing perlite or vermiculite are also great choices.
Most seeds prefer to germinate somewhere between 60 and 80 degrees Fahrenheit, including the air and the soil. Certain wildflower seeds and early-season crops prefer a cooler temperature, but you should be directly sowing those types outdoors in early spring anyway. So, when crafting an indoor seed-starting environment, aim to keep the temperature within that range. I always recommend a heating mat to ensure warm soil. Cold soil will result in little to no germination and even rot and fungus.
Water is a critical catalyst in the seed germinating process. Without water, a seed will not germinate. Period. I think this one is fairly self-explanatory. You want to have plenty of water in the beginning stages of seed and seedling development. Keep the growing medium constantly and consistently moist.
Of course, seeds need time to germinate. Become aware of how long each seed you are planting is expected to take. Some germinate in 2 days, while others take 2 weeks or more. Patience is key for those longer types. Keep the soil moist throughout the germination period.
Some seeds need light to germinate. Lettuce, begonia, and petunias, for example, are some common seeds that will not germinate unless they are exposed to some light. The main reason I include light in this list is that immediately following germination, it is critical for seedlings to be exposed to 6-12 hours of bright light. Sometimes, a windowsill can accomplish this, but most often, a grow light is needed to be successful. Even if you jump the germination hurdle, the seeds will quickly die without proper lighting.
Right off the bat, let me remind you that most typical garden seeds do not need any kind of treatment. This means you can take them straight from the packet and plant them in the soil, and they will germinate. However, some seeds need stratification in the form of cold or manually breaking the seed coat before they can germinate. Some seeds also benefit from soaking in water before planting in the soil. While some seeds need these treatments, others are unphased by them.
The short answer is probably not. Cold treatment, also known as cold stratification or vernalization, is often used as a signal for the seeds to know that winter has passed, spring is here, and it is safe to germinate. The most common group of plants that need cold treatment are wildflowers native to cold climates, such as coneflower, lupine, and some types of milkweed. However, even then, they will often germinate without it. When it comes to a vegetable garden, you don’t need to worry about it. The seed growing instructions should say if your seeds need cold treatment.
Again, the short answer is probably not. Scarification is the process of manually breaking the seed coating by roughing it up with sandpaper or acid or using a knife to nick the side in order to increase germination rates. Some seeds that have a hard, thick seed coating may need to be scarified somehow. However, scarification is most commonly required by tree and shrub seeds. If your seeds need scarification, the seed packet instructions should say so.
Seed soaking is quite the debate these days. In short, it might speed up germination if you want to try it. The first step in the germination process for a seed is called imbibition, where the seed absorbs as much water as possible. Typically, seeds do this with water in the soil or growing medium. However, soaking the seeds in straight water makes it easier for the seed to absorb more water quickly, reducing germination time in the soil.
We typically recommend soaking large or hard seeds, such as sunflowers, peas, grains, and many of the seeds used for microgreens. However, remember that you should never soak coated, pelleted, or treated seeds. If you do so, the coating will come off, making it even more difficult to plant and germinate them. Generally speaking, very small seeds don’t need soaking.
1. Why are my seeds taking so long to sprout?
First, review the five factors listed above and make sure you have them all right. The answer might be to just keep waiting. Some seeds that are similar may take drastically longer times to germinate. Even within the same variety of seed, some seeds can take a few days different. Did you make sure to plant more than one seed per hole? If you need the seeds to germinate faster, you could soak them before planting in the future. If they continue to not sprout, see the next FAQ.
2. What if my seeds didn’t germinate?
Go through the five factors listed above and make sure you have all the factors right. Do they need more time? Was the soil the right temperature? Did they remain consistently moist? Did you plant 2-4 seeds per cell or hole? Did you use a sterile growing medium? If you did all of these things right, it could be because the seeds were old or stored improperly. If you know that isn’t true, then contact your local extension office and let them know exactly what you did and what you observed. They may be able to help guide you through alterations to your seed-starting process or help you better understand the needs of your specific seed.
3. What if some of my seeds germinated but others didn’t?
This is called the germination rate. Firstly, they may just need more time. Some seeds (even of the same variety and batch) can germinate at wildly different intervals. Some pepper seeds only take 5 days, while others take 12 days. Patience could be the answer. Also, sometimes seeds are just duds. Even the best seed producers have a small percentage of seeds that simply will not germinate despite having optimal conditions. This is why when you read instructions for seed starting, most companies suggest you plant 2-4 seeds per hole and then thin them to only 1 after germination takes place. This ensures you get at least one good seedling right off the bat.
4. My seed germinated, but the seed shell is still attached to the cotyledon. Should I remove it?
No! Just leave it. The seedling will eventually shed it on its own and then it may even be stronger for it.
5. Should I use the paper towel method to germinate seeds?
I only recommend the towel method if you are concerned about germination rates. There is really no other reason to do it. The paper towel method involves soaking paper towels in water, laying the seeds on the towel, covering it with another wet paper towel, and letting the seeds sprout. This method allows you to clearly see which seeds germinated and which didn’t. Generally, I wouldn’t bother with it because it’s just an extra step.
6. How deep should I plant seeds?
Every seed has a different requirement, but the general rule of thumb is to plant the seed twice as deep as it is big. So, pumpkin seeds can go about an inch deep, while tiny carrot seeds should be barely covered by soil. Just be aware of whether a seed needs light to germinate or not. See above for more details on that. Always plant multiple seeds per cell or hole.
7. Should I cover my seeds with a dome of plastic wrap for germination?
In my experience, this is beneficial, but it isn’t critical. Placing a plastic dome or wrap over a tray of seeds helps retain moisture and heat, which helps the seeds germinate faster. Without it, you just have to be extra careful that the soil doesn’t dry out and that the tray stays warm. If you choose to use a covering, be sure to take the lid off immediately after you see the seed sprout through the soil surface; otherwise, it will block light and make the seeds leggy.
8. How far in advance should I start my seeds?
This entirely depends on the seed. Each seed typically comes with a recommendation for indoor starting, which can be anywhere between 2 and 12 weeks before the last spring frost in your area. True Leaf Market has some fantastic starter guides for everything from vegetables to flowers to cover crops. Those booklets and guides should have the information you’re looking for.
9. Why did my seeds stop growing?
Firstly, take a moment to check the variety you are growing and see how long they usually take to grow. The first time I grew peppers from seed, I asked this question. It turns out that they just take a long time. If you are sure they have seriously stopped growing, go through the five factors above again. Do they have the perfect environment, including enough light, heat, and water? Additionally, improper watering can lead to growth problems. Overwatering can cause root rot, while underwatering may prevent the seedlings from getting the moisture they need to continue developing. Once these needs are met, consider feeding with a water-soluble fertilizer to stimulate foliage development.
10. Why did my seedlings collapse or wilt even though they are green?
If you see this and you know the seedlings have enough light and water, you are likely seeding a fungal disease called damping off. Damping off is a very common disease that affects new seedlings. To prevent this disease, use sterile soil, avoid overwatering, and ensure proper air circulation. Providing good drainage, allowing the soil to dry between waterings, and avoiding overcrowding can also reduce the risk of damping off. Unfortunately, once they have been affected, they will not recover, and you will need to start over.
11. Why are the stems so long and/or white?
The number one cause of this is insufficient light. When seedlings don’t receive enough light, they stretch upwards in search of it, resulting in tall, spindly growth. Using a grow light positioned a few inches above the seedlings for about 12-16 hours a day can prevent this. Depending on how long they have been without insufficient light, you might have to start over. Seedlings that are affected often appear healthy at first but then develop weak, water-soaked, or mushy stems at the soil line. Eventually, they collapse and wilt, even if the leaves still appear green.
Another possible cause is starting the seeds too close together, which leads to light competition. High temperatures can also contribute to leggy growth, as seedlings develop faster in warm conditions, but without adequate light, they become weak and elongated.
12. Is it bad if I have green algae growing on the soil surface?
Green algae on the soil surface isn’t necessarily harmful to seedlings, but it indicates overwatering and poor air circulation. While algae itself doesn’t harm plants, it can compete for nutrients and block light from reaching the soil, potentially stunting seedling growth. Algae thrive in consistently moist conditions, so allowing the soil surface to dry out slightly between watering can help. Improving ventilation and reducing humidity can also prevent algae growth. Using a fan to circulate air and ensuring trays have proper drainage are helpful steps in managing this issue.
13. How long can I store seeds and still germinate them?
If seeds are stored in a cool, dark, dry, and pest-free environment, they can last about 5 years. The key to remember here is that the seeds will very gradually lose viability. So, the first year you have a seed packet, you should get the highest percentage germination rate (if they’re from a trusted company like True Leaf Market), but after 6 years of proper storage, some of them may still germinate, but the percentage may be lower. Always plant multiple seeds per cell or hole to accommodate for this natural decline.
For example, my grandmother had a #10 can of seeds that were completely sealed in her emergency prep supplies for over 20 years. She decided to get them out and see if they were viable. She planted a lot of tomato seeds, thinking that, hopefully, a few of them would germinate. Long story short, by the end of the summer, she had tomatoes coming out of her ears. However, someone in the same situation might only get a couple of viable seedlings. It is impossible to tell sometimes.
14. What are all the materials I need to start seeds indoors at home?
Every gardener has their own special mix, but these are the essentials:
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