Beginner’s Guide to Seed Starting: How to Start Seeds

In this comprehensive guide to seed starting, we’ll cover everything you need to know—from supplies to troubleshooting—to set you up for gardening success!

Starting seeds is one of the most rewarding steps in creating a thriving garden.

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Seed starting is the process of germinating seeds indoors, to give plants a head start, before transplanting them outdoors into your garden. This method is particularly beneficial in areas with shorter growing seasons, as it extends the time plants have to grow and produce.

I’m gardening in zone 6b, and our growing season lasts from mid May to the beginning of October. Starting my seeds indoors gives me more time for succession planting things like broccoli, as well as plants like tomatoes that take longer to get growing.

By starting seeds indoors, you also have greater control over the germination process, soil temperature, and growing conditions, which can lead to healthier plants and better yields. I also tend to have better success and care for my seedlings because of how close my plants are to me when they are growing indoors!

Before you begin, there are some tools and equipment that will make the task much easier. Keep in mind that many of these things are an investment that you can use year after year after purchasing them.

Some of these tools are quite vital, like your seed packets and growing medium, but others are not necessary to get started: like a heat mat or soil thermometer.

When choosing the seeds you’d like to grow for your garden, consider what you will actually want to use once they grow!

For example, my family isn’t a fan of kale or eggplant…at all. I’ve grown some of the most beautiful kale I’ve ever seen, however, it became a labor of love for my chickens rather than my children. Fortunately for me, my egg layers love kale, but I grow much less of it now that I know we won’t use it in our kitchen.

It’s also important to note the difference between hybrid seeds and heirloom seeds.

Hybrid seeds are grown through a controlled pollination process and often won’t reproduce a reliable result if the seeds are saved from your garden. If you want to have a sustainable seed saving process, these might not be for you.

However, hybrid seeds are also often bred for vitality and vigor. So if you aren’t worried about seed saving, these can produce extremely hearty plants!

Heirloom seeds are open-pollinated and are classified as “heirloom” after growing for 50 successive generations. Because of their long lineage, their seeds can be saved at home and grown for your own future garden generations!

I personally use heirloom seeds. I love the romantic stories that often surround the different varieties and seed saving at the end of the season saves me tons of money every year.

It is also important to read the information on the seeds you are interested in purchasing. Some varieties do better in specific regions.

Your seed packet should also tell you the planting information for each individual seed.

Some seeds need to be planted extremely shallow, and will note that on the packet, while others will need to be planted 1/2″ or more below the surface of the soil.

Seed-Starting Mix

Seed tray or cell trays

Grow Lights

Grow Light or Fluorescent Lights are needed to provide enough light for seedlings to grow strong and healthy. The most important thing to know when choosing a grow light is if they have the following key features:

• Lumens: a light intensity of ideally 2,000-5,000 lumens for seed starting to support healthy growth.
• Kelvins: opt for a full-spectrum light to mimic natural sunlight. Light labeled as “daylight” or with a color temperature of 5,000-6,500 Kelvin works best.
• LEDs: many DIY and cheap instructions for seed starting will give fluorescent lights as an option, however LED lights will not get as hot or use as much energy as fluorescent lights can. If you already have the fluorescent lights, or only have the budget for those right now, those will work, but consider investing in the LED’s when you can.

The lights I use are these 4 ft LED’s that I can put on the undersides of my shelves.

Less Important Supplies for Seed Starting

These supplies will only streamline and make your seed starting journey easier.

However I know as well as anyone that this endeavor can feel as daunting as it does expensive when starting out, so I didn’t start with these supplies, but only added some in later.

Light Timers

Adding timers to your lighting set up can make things much easier for you, the gardener. They are not necessary, but I find this to be the most helpful “non-essential” tool.

Seedlings need 12-16 hours per day of light to grow properly. It can be a hassle to turn your lights on and off at the exact same every day.

These are the timers I use to keep track of my seedlings’ light exposure.

Humidity Dome

Helps maintain high humidity during the germination process. Not necessary, but can help protect against temperature fluctuations.

You can also use plastic wrap to mimic a humidity dome if you want to experiment with adding humidity without adding more supplies to your list just yet.

Be sure to monitor seedlings closely when using a humidity dome, as constant moisture can promote diseases such as dampening off.

SOIL THERMOMETER

Helps monitor soil temperature, a key factor in seed germination. This is one tool admittedly I still don’t use.

Most heat mats will come with a soil thermometer to regulate the mat’s temperature itself, and even still, not all of my seedlings will even fit on a heat mat.

My home is almost always in optimal range for growing plants, so I don’t worry much about keeping track of this.

2. Choose Your Seeds

Opt for fresh seeds with high germination rates. Vegetable seeds like tomato seeds, pepper seeds, and leafy greens are great for beginners. For flowers, consider annual flowers like marigolds or zinnias. Check the seed packet for specific growing requirements, like planting depth, and recommended start dates.

3. Prepare Your Seed-Starting Mix

Moisten the seed-starting mix with water until it’s damp but not soaked. I always think of a rung out dish rag. It isn’t dripping through your fingers while you hold it, but if you squeeze it, water will drip a bit.

You want to make sure you moisten the growing medium before you add the seeds, as dry soil can be hydrophobic, meaning it’s averse to water before being thoroughly wetted.

Fill your seed trays or individual containers with the mix, leaving about ½ inch of space at the top. Avoid using garden soil, as it may contain weed seeds and harmful bacteria. As stated in the “what you’ll need” section, I purchase a gardening mix from my local garden store.

4. Plant Your Seeds

Refer to the seed packet for planting depth. As a good rule of thumb for seeds without the information available, plant seeds at a depth twice their size. Cover small seeds lightly with soil and pat gently to ensure contact. Large seeds, such as squash or pumpkin seeds, will require slightly deeper planting.

5. Provide Heat and Humidity

If using a heat mat or humidity dome, prepare these tools for your seed trays. As stated in the “what you’ll need section, these tools aren’t necessary, but can be helpful if your growing area isn’t a controlled temperature.

The optimal temperature for seed germination is typically 65-75°F, so if your home maintains this temperature, you can definitely do without the heat mat and humidity dome!

A warm, moist environment speeds up the germination process for most seeds.

6. Ensure Proper Lighting

As soon as seedlings emerge from the soil, you’ll want to place them under a grow light or fluorescent light for 12-16 hours a day. You don’t want them to be exposed to light 24/7, as this doesn’t happen in their normal growing environment.

Using a timer for the lights is extremely helpful to keep things regulated. Check the “what you’ll need” section above for more information on those tools.

Ensure the light source is positioned a few inches above the seedlings to prevent leggy growth.

A south-facing window can also work in a pinch, but artificial light provides more consistent results.

7. Water Carefully

Use a spray bottle to keep the soil surface moist before germination, but not soggy.

Avoid overwatering, as wet soil can lead to fungal diseases like damping-off. Check the soil daily to ensure it is slightly damp for your seedlings.

I prefer to bottom water my plants. This means I fill the bottom tray of my seed starting set up with enough water for my seedlings to suck up through the drain holes. Bottom watering allows me to avoid getting my seedlings themselves damp.

I also like to let my soil to dry out a bit before watering them again. This takes about a week when the seedlings are small, and less time as they get larger and consume more water.

8. Thin Seedlings

Once the seedlings sprout, keep an eye on how many you have in each cell.

Once the seedlings develop their first set of true leaves, you’ll want to thin them out so that there is only one seedling per cell.

Thin seedlings by snipping weaker plants at the soil line to give the strongest ones room to grow. Crowded seedlings can compete for light and nutrients, leading to weaker plants overall.

9. Transplant to Larger Containers

If the seedlings outgrow their trays, move them to larger pots filled with potting soil. Handle seedlings gently to avoid damaging the delicate stems and roots. This step allows the plants to develop stronger root systems before outdoor planting.

Plants like tomatoes will root out of their stems if planted more deeply, so you can strengthen them significantly if you bury them a bit deeper when you pot them up.

10. Harden Off Before Transplanting

Before planting your seedlings outdoors, harden them off by gradually introducing them to outdoor conditions over 7-10 days.

Start with a few hours of indirect sunlight and increase exposure daily. This step helps reduce transplant shock and prepares seedlings for their new environment.

I usually start with a partially shaded area that has low wind exposure, and work my way up with more light and wind exposure until it’s time to plant out.

Troubleshooting Common Seed Starting Issues

Even with careful planning, seed starting can come with challenges.

Let’s delve into some of the most common problems, why they occur, and step-by-step solutions to address them effectively.

• Poor Germination: If your seeds aren’t sprouting, it’s often due to incorrect soil temperature or old seeds. Ensure the soil temperature matches the seed’s needs (use a soil thermometer to check). A heat mat can help maintain consistent warmth. Always use fresh seeds stored in a cool, dry place, and test older seeds’ viability by placing them on a damp paper towel to see if they germinate.
• Leggy Seedlings: Seedlings become leggy when they stretch toward insufficient light or are exposed to high temperatures. To fix this:
  1. Improve Lighting: Position grow lights 2-3 inches above the plants and provide 12-16 hours of light daily. Adjust the light height as the seedlings grow.
  2. Transplant Deeply: Gently replant the seedlings into larger containers, burying part of the stem to stabilize the plant and encourage root growth along the buried stem. (note: this method only works for plants that can root out of their stems, so be sure to find out if your leggy seedlings fit in this category before burying any of the stem.)
  3. Cool the Environment: Lower the room temperature to 65-70°F. This slows elongation and promotes sturdier growth.
  4. Strengthen with Airflow: Place a small fan near the seedlings to simulate a breeze, which strengthens stems.
• Damping-Off Disease: A fungal disease that causes seedlings to rot and collapse at the soil line. To prevent this:
  1. Avoid overwatering and ensure trays have proper drainage.
  2. Water seedlings from the bottom to keep foliage dry.
  3. Use sterile seed-starting mix and clean trays before use.
  4. Increase air circulation with a fan.
• Yellowing Leaves: Yellow leaves often signal overwatering or nutrient deficiencies. Check for soggy soil and reduce watering if needed. If the seedlings have developed true leaves, consider feeding them with a diluted organic fertilizer, like this seaweed one that I use, to replenish nutrients. Be sure to follow the fertilization directions properly to avoid burning your plants with an over-concentrated fertilizer.
• Stunted Growth: If seedlings seem stuck, it could be due to root-binding, insufficient light, or poor soil quality. To address this:
  1. Transplant seedlings into larger containers to give roots more space.
  2. Check light conditions and ensure 12-16 hours of bright light daily.
  3. Refresh the soil with a nutrient-rich potting mix or organic fertilizer.
• Pest Problems: Tiny pests like fungus gnats or aphids can sometimes infest seedlings. Combat pests by:
  1. Sprinkling the soil surface with diatomaceous earth or sand to deter gnats.
  2. Using neem oil to treat aphids or mites.
  3. Keeping the growing area clean and free from decaying plant material.

Selecting the Best Seeds for Your Garden

When choosing seeds, consider your gardening goals:

• For Early Spring Crops: Start cool-weather vegetables like lettuce and kale.
• For Summer Bounty: Plant warm-season crops such as tomatoes, peppers, and cucumbers.
• For Annual Flowers: Try marigolds, petunias, or cosmos for a splash of color.
• For Herbs: Basil, parsley, and dill are easy to grow and useful in the kitchen.

Seed starting is a rewarding way to take control of your garden, giving you a head start on the growing season. With the right supplies, a bit of patience, and this guide to seed starting, you’ll soon be enjoying the satisfaction of nurturing plants from seed to harvest!

Grab your seed packet and let’s grow!