How and When to Start Seeds Indoors
Starting your seeds indoors can help put you ahead of the curve in spring. Here are some tips on getting your seeds started indoors in the coming months.
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There are many benefits and drawbacks to starting seeds indoors versus direct sowing them. In colder climates, it gives you a definite advantage. As soon as the weather warms up, you can plant those starts rather than waiting for seeds to germinate. However, some plants have a long tap root, which makes direct sowing far more effective.
We want to grow the strongest, most robust plants possible. Knowing when to start, which seeds are best started indoors, and how to do it are important. Let’s talk about when you should get rolling and how to grow your seedlings indoors best.
Timing is Important, But It’s Not Everything
The question of when doesn’t have a hard and fast answer because not every plant performs the same way. There is also the question of climate: When are you expecting the last frost, and when will the ground thaw?
The best advice I can give you in terms of planting time is to read your seed packets. These will typically tell you whether it’s recommended to start indoors or directly sow seeds outdoors. They will also give an idea of how many weeks ahead you should start and how long to wait before transplanting.
Some seeds are frost-tolerant and don’t mind cold soil. Others, not so much. Some need the soil to warm to a certain temperature, or they will die back or underperform. Because of this, it’s always a good idea to follow instructions for your specific seeds.
You won’t typically start all seeds indoors and transplant them all at the same time. Depending on the species, you should start spring seeds between 4 and 12 weeks ahead of your last anticipated frost date. That’s why it’s important to follow those guidelines on your seed packets. Please see our charts above for recommendations for many seeds.
The average last day of frost (32°F/0°C or less) is defined as the first day in spring on which there is less than a 50% chance a frost will occur. This information is crucial when planting a garden. To find out your average last day of frost, you can use the National Gardening Association’s frost date calculator. Call your local independent garden center, or contact your local Cooperative Extension office. Also inquire about the average date of the first fall frost for late season planting.
I want to briefly touch on fall planting, as there are many plants you’ll want to start in late summer and plant in early fall. For these, you may want to do a bit of extra research. We are here for you on that front as well and have lots of information on which plants grow best in the fall, which in the spring, and which you can plant in both seasons.
Do Some Digging
When I say do some digging, I’m not talking about soil. I’m talking about research. One of the most beneficial things you can do before starting seeds is to learn about that plant’s specific needs. As I mentioned earlier, most seed packets will provide much of the information you need.
Some questions to answer when selecting which plants to grow include:
- What zone do you live in, and what plants grow there?
- What plants don’t thrive in your climate and environment?
- What temperature do your seedlings need in order to transplant them?
- When is your last anticipated frost date?
- Will your seedlings be frost-tolerant?
- What seeds are better to sow directly in the garden?
Select seeds that you know will thrive in your environment, and then you can think about varieties.
Select Your Seeds
The most exciting part of this process is selecting the varieties. Do I want purple tomatoes this year or classic red? What type of okra is spineless and better for pickling? For most plants, the sky is the limit.
It’s also important to purchase your seeds from a reliable source. I’m not suggesting that you shouldn’t take a chance on those heirloom seeds your friend shared with you, but it’s a good idea to buy from a trusted source.
Collect Your Supplies
Before you get started, determine which supplies you already have and which you need to purchase. Consider what items around the home and garden you can repurpose for other functions.
There is a wide range of starting cells and trays at different price points. The difference in their longevity typically corresponds with the investment. Thin plastic trays will last one, maybe two seasons, if you take good care of them. Peat pots are great for the environment, but they are single-use. Stronger, reusable cells are a good investment for any veteran gardener who knows they will be growing for many years.
Plastic bags can help maintain a moist greenhouse environment for your seedlings, a great reuse of a household product. However, you may want a reusable product that will serve this purpose for years to come. In that case, I recommend plastic covers designed to fit your seed trays.
Some other products that may come in handy depending on your space and environment are a heating mat and grow lights. If you’re starting any that need warm soil to germinate, a heating mat is a good investment. They are inexpensive and speed up the process significantly.
Grow lights are a must if you don’t have a greenhouse or brightly lit indoor space where your seedlings won’t get in the way for the months they are indoors. Grow lights enable you to set up in the garage, a closet, or any out-of-the-way space. A timer is helpful when using grow lights. These make it possible to avoid forgetting to turn your lights on and off, as most plants need cycles of light and darkness.
Prepare Your Potting Media
Potting media is an important factor in starting healthy seeds indoors. Fine roots grow best in a loose potting mix. Commercial starter mixes are great for this purpose. Most are soil-free mixtures of peat, fertilizer, vermiculite, and perlite. These loose materials help avoid root rot and stunted growth from compacted soil-based media.
These materials are a good place to start if you prefer to make your own mixes. If you intend to do a lot of planting, it can be more economical to purchase larger quantities of peat, perlite, vermiculite, and fertilizer. If you’re starting small, those things can take up a lot of space, so a good starting mix will be perfectly fine.
Consider Depth and Soil Temperature
Another factor to consider before you get going is the depth at which you should plant each type of seed. This usually comes down to whether or not they need exposure to light in order to germinate. Some need it, while others germinate in the dark.
Those that germinate in the dark typically need to go a certain depth beneath the soil. These seeds are usually larger in size. You’ll hold off on using your grow lights until after they sprout. For others that need light to sprout, you’ll want to sow those on the surface and use those grow lights from the very beginning. These seeds are typically very tiny.
This information will commonly show up on those packets, as well. If not, this is an important factor in germination, and you should do the research to make the determination. Most need some light, and you’ll either surface sow them or just slightly cover them with soil. Those that need darkness to germinate are less common.
Soil temperature is another important factor in germinating your seeds. Look for this also on your seed packages. If it’s not noted there, check the company’s website for further information. This factors into whether certain seeds are best planted in the fall when the soil is warm and the air is cool. That will mainly apply to cool-weather crops and perennials, though.
This is a major benefit of starting seeds indoors. If you sow these plants outside, you have to wait longer for warmer soil. By starting them indoors, you have more control and can get them growing long before you can transplant them outdoors. For many spring plants, cool but not cold soil is fine. But, for some, like tomatoes, basil, and peppers, 65°F (18°C) is the minimum at which they will germinate. That’s where that heating mat comes in handy.
Identify the Right Spot for Your Seeds to Germinate
It’s time to choose a location to set your trays and wait for the magic to happen. This goes back to whether they need light or darkness to sprout. Most need bright but indirect light. Young, tender leaves will burn more easily than more established ones. Even for plants that require full sun, indirect light is best at this stage.
If you’re using a grow light, this is less of a concern as they are less intense than the sun can be at certain times of day and from certain directions. For those that need darkness, this is only true until they break the surface and then move into the light.
Keep your trays out of drafty spaces and those where the temperature fluctuates sharply. You want to maintain an environment that is as consistent as possible, which minimizes stress on young plants.
Maintain the Correct Moisture Level
Moisture is an important factor in preserving the seeds and roots of your seedlings. Keep in mind that moisture comes in two forms. It’s not just about the soil. Humidity is important for some young plants, while others rot more easily.
Let’s start with soil moisture, though, as this is the first concern you’ll encounter. Some seeds take in moisture quickly, sprouting fast as a result. These are typically those with thinner or more flexible outer coatings. You’ll typically not need to soak these to aid in germination, and they will pop up faster. These rot more easily, so it’s important to avoid wet potting media.
Others, however, require more moisture to germinate. These are usually the ones with ticker, harder outer coatings. Think about sunflower seeds or corn. They have thick, hard shells that keep moisture out. They are better for storing but take longer to sprout. It’s imperative to maintain moisture in the soil for these.
Those with tougher shells also benefit from soaking before planting. Soak them overnight in water to give them a faster start. Some also benefit from nicking, filing, or otherwise making a small opening in the shell. This gives the sprout a spot to break open more easily.
After planting these, keep the soil moist and maintain some humidity around them with a humidity dome. Water from the top until a week or two after sprouts appear. After this, you can begin bottom watering if you prefer. This helps prevent the soil from drying out too quickly.
Practice Patience
Now comes the hard part. The waiting game is always tough for me. I check on my babies daily to see those first little green bits peek out of the dirt. Remember the adage: a watched pot never boils. It’s not true, of course, but the concept holds in this situation. If you pay too much attention, it will seem like forever.
Remember that those with thinner coatings will pop up faster, and those with hard shells will take longer to break through. There are some exceptions, but in general, this is how it works. Soaking those hard-shelled seeds in water will help. Adding a bit of liquid fertilizer can also speed the process and give them a little boost of nutrients.
Know When to Transplant
Finally, it’s good to know what stage you should transplant each type of seedling. After starting seeds indoors, most require a hardening off period to minimize stress before moving outside. This is the process of acclimating your young plants to the outdoor climate.
Effectively acclimating your plants to the outdoor environment is an important step. It will lead to stronger plants that grow straighter and faster. While carrying out this process, growth will slow, but stems and leaves will thicken and become stronger.
For all but those plants that are frost resistant, wait until the chance of frost has passed before moving your seedlings outdoors. Then, increase the amount of time they spend outdoors gradually. Put them out for a couple of hours the first day, and increase it by and hour or two daily.
Location is important, as you want them as close to their soon-to-be to be home as possible, but they will need some protection. Cold or strong winds can do a lot of damage to those that are not yet hardened off. Make sure to continue watering through this process. The transplant once thy are spending all day outdoors.
If you follow this plan, and stay on top of dates, temperatures, light, and moisture, your new plants should have a strong and healthy growing season. Happy planting!
