Seed-Starting for Beginners: The Complete Guide

Seed-starting is often where beginner gardeners start their growing journey. Unfortunately, it’s also a massive source of frustration.

Although seed sowing is not difficult, there are many ways it can go wrong, particularly if you don’t have the right tools or knowledge about the plant you’re growing. Something as simple as sowing at the wrong depth can leave you with a tray full of ungerminated seeds and no plants, wondering what went wrong. And no, that doesn’t mean you’re a ‘black thumb’. It just means you need a little more information about the seed-starting process.

If you’ve never started seeds before, you’re in the right place. I’m going to break down the tools and supplies you need, the preparation to complete before you start, and each part of the process step by step. Understanding the basics is essential to seed-starting success.

What You’ll Need

Before you start sowing seeds for the first time, you’ll need to grab some supplies. Although there are ways to simplify or DIY, having the right tools and equipment makes seed-starting so much easier.

Seeds

First, you can’t sow seeds without the seeds themselves. You can collect them from your garden, use leftovers from a previous season, or purchase new seeds of your favorite varieties. Purchasing new seeds will give you the highest chances of success as there is more control over storage and viability.

Before you choose what you want to grow, consider your climate. Your USDA Hardiness Zone will determine what perennials can easily grow outdoors and when. Although there are ways to grow perennials outside your zone with extra protection, sticking within your climate limitations is best for beginners. Annuals have a one-year life cycle (though some tender perennials may be considered annual in your area). For these, follow your seed packet instructions on the necessary outdoor temperatures before transplanting outside.

Now for the fun part: selecting varieties. This comes down to personal preference, your garden design, and the location you want to fill. I like to scroll through a wide selection for inspiration before making a final decision—you never know what new varieties may take your fancy. For those growing edibles, stick with fruits and vegetables you actually enjoy eating so you don’t waste your harvest.

Containers

Once you’ve purchased your seeds, you’ll need something to sow them in. There are many options here, from DIY containers to soil blocks. But for beginners, I always recommend seed-starting trays.

Seed-starting trays are designed to make sowing as simple and successful as possible. You don’t need to worry about drainage as you would with DIY options. Plus, they are reusable, limiting waste in your garden.

Another way to limit garden waste is to choose biodegradable containers or use soil blocks. After sowing, these are transplanted straight into the ground as is. This is a great option for species prone to transplant shock that don’t handle root disturbance well.

If you prefer to go the DIY route, make sure your container has enough drainage holes to remove excess moisture. Lack of drainage will prevent root growth and encourage fungal disease. Fill the container with soil and run water through it to check drainage before sowing.

DIY containers also need to be deep enough to hold soil and provide space for roots to grow. Aim for a minimum of two inches deep.

For those reusing seed trays or other containers, clean them well before you start. Although the risks are not particularly high, it is possible to transfer problems from old soil, like pests or diseases, if you don’t clean your trays.

Soil Mix

To give your young seedlings a strong foundation for growth, selecting the right soil mix is essential. The most important characteristics to consider are moisture retention and texture. The soil needs to hold enough moisture to promote germination (without becoming soggy) and it should have a fine texture to provide as little resistance to root growth as possible.

You’ll find specialized seed-starting mixes available online or at your local nursery. It’s generally best to avoid regular potting mixes as they can have a chunky texture that negatively impacts germination and fine root growth.

If you’re sowing seeds regularly, it’s cheaper to make your own mixes. The general ratio of ingredients is:

• One part moisture retention materials
• One part drainage materials
• One part compost

What you use for moisture retention and drainage is up to you based on what you have on hand. As an example, a DIY seed-starting mix recipe could include:

• One part coconut coir
• One part perlite
• One part compost

Seeds have all the nutrients they need to germinate successfully, so don’t worry about adding fertilizer to your mix. You’ll only need to consider additional nutrients once the plants have sprouted and grown a few inches.

Grow Lights

If you’re sowing indoors or in a protected area away from direct sun, grow lights are a must-have. While many seeds may germinate in darkness, they need plenty of direct sun when they poke through the soil to promote strong early growth. Lack of sunlight will lead to weak stems and floppy seedlings.

Grow lights simulate direct sun to provide the energy young seedlings need to establish. The consistent light from overhead encourages stems to grow directly upwards, limiting issues with lopsided growth when sowing in front of a window.

Plus, seed-starting grow lights are often small enough to fit on a countertop and have built-in timers that provide exactly the right amount of light for your chosen plants.

Grow lights are a pricey investment compared to the other supplies needed, but they are worthwhile, especially for beginners. If you’re not ready for the investment just yet, make sure you leave space in front of a south-facing window that receives plenty of direct light throughout the day. Sunlight is one thing you don’t want to skimp on when seed-starting.

Heating Mat

Heating mats are another nice-to-have that aren’t required for seed-starting success, but certainly make success far more likely.

Warm-season seeds need warm soil to trigger germination, mimicking the change of seasons they experience in their natural habitats. If you’re sowing indoors in the middle of winter or early spring, that warmth is hard to come by. Even if you have all the other seed-starting conditions met, your seeds won’t germinate if the soil isn’t warm enough.

Some types need much warmer soil to germinate, like tomatoes and eggplants. These heat-loving crops germinate best when soil temperatures are around 75° or even higher. To achieve this temperature in the colder months, you need a heating mat.

Heating mats are placed under seed-starting trays to gently warm the soil and keep it at a consistent temperature. They aren’t necessary for sowing every time but are incredibly helpful for warm-season crops and winter sowing indoors.

Seed-Starting Preparation

With supplies gathered, it’s time to move on to preparation. Don’t rush to toss your seeds into the soil just yet—there are a few preparation steps to complete first.

Timing

Seeds are generally available to purchase all year round. However, that doesn’t mean you can sow them as soon as they arrive at your door. Plants need to be sown according to their season to avoid any mishaps after transplanting.

Luckily, the information on the seed packet will tell you which months are suitable for sowing. This is particularly important in spring when the risk of frost looms. You don’t want to sow outdoors too early, only to have them killed off by temperature drops as soon as they germinate.

That’s why it’s vital to know your predicated last frost date for spring sowing. This date differs per region and will tell you when you can start sowing outdoors.

If you want to get a head-start on the growing season, start indoors a few weeks before transplanting time. Some are best sown eight weeks before last frost, others slightly sooner. Check the instructions for your specific species to determine the right timing.

Sowing too late is also a concern. Changes in environmental conditions may shorten the season, killing the crops before they have a chance to mature. When you’ve gone to the effort of sowing seeds, it’s incredibly disappointing to have the plant die off before you get a chance to harvest.

The final thing to consider when it comes to timing is succession sowing. While you can sow all your seeds at the same time, it’s better to space them out in two-week intervals. The plants will mature at different rates, flowering and fruiting at different times. This is helpful in vegetable gardens to provide a continuous harvest rather than a massive one all at once.

Location

Next, consider your location. If you’re sowing indoors, clear a space and set up your grow lights and heating mat. The seed trays shouldn’t be too crowded or in a corner with little movement as lack of airflow increases the risk of problems like damping off. If you need more airflow indoors or in a greenhouse, use a small fan to circulate air.

If you’re direct sowing outdoors, prepare the area by amending the soil with compost (and any other amendments needed to boost soil health). Also clear the area of any weeds, as the competition for space and resources will hinder seedling growth.

Soaking, Scarification, and Stratification

After preparing the location, you may need to prepare the seeds themselves. This doesn’t apply to all species, and the type of preparation will depend on what you’re growing.

Some types have an extra thick coating designed to protect them in harsh environments over winter. This prevents germination until the time is right for the plants to emerge in spring. While this is helpful in nature, it isn’t as helpful for gardeners.

To trigger germination, you need to break into this tough exterior to allow moisture and warmth to penetrate the seed. This is done by a process called scarification. In simple terms, it involves nicking or filing the outer shell before sowing. Nasturtiums, beans, or morning glory all benefit from this treatment.

Scarification is often combined with soaking. This triggers germination and improves germination rates in larger seeds like pumpkins, cucumbers, and sunflowers. Soak in lukewarm water for around 6-24 hours (depending on the plant) right before sowing. Not all seeds benefit from soaking, so only follow this step if it’s recommended for your crops.

Other plants may need a period of cold to trigger germination, known as stratification. This mimics the temperature drops these plants experience in nature that encourage germination when temperatures rise in spring. To stratify your seeds, sow them outdoors in fall or place them in a refrigerator for several weeks in a damp medium before sowing in spring.

How to Start Seeds

The previous preparation steps should be completed right before you plan to sow. This is important for seed prep, as you need to get the seeds into the soil right after soaking or scarification. Follow these easy steps when you’re ready to start.

Prepare the Soil

Step one is preparing your soil for sowing. Grab your seed tray or container and fill it with your seed starting mix. Press the soil down gently to create a level surface, but don’t compact it so much that you restrict airflow and drainage. Lightly moisten the soil with a watering can or spray bottle to prepare for planting.

For direct sowing, mix any amendments like compost into the top layers of soil to improve texture. Level out the surface and remove any weeds or garden debris like stones that may hinder germination.

Check Spacing

When you’re sowing in seed trays, spacing is already decided for you. However, if you’re sowing straight into the ground outdoors, you need to consider spacing. This prevents overcrowding and competition later on, reducing the risks of growth problems and diseases.

The recommended spacing will depend on the particular variety you’re growing. Luckily, this is usually indicated on the back of the seed packet. Measure the planting area and follow the guides, particularly if you’re planting multiple rows at once.

If you are growing a crop with lower germination rates, you can sow multiple seeds closer together in the soil. As the seedlings develop, thin them to the correct spacing by keeping the strongest performers and removing the rest.

Plant at the Right Depth

Planting depth is another factor that impacts germination and later growth. Some seeds prefer to be planted deeply and completely covered, while others are happy laying on the soil surface with exposure to light. Sowing at the wrong depth may prevent germination or leave roots exposed, impacting growth.

As a general rule, plant seeds at a depth of twice their largest dimension. That means larger seeds should be planted deeper than smaller ones. If you’re not sure, check the sowing information for your specific variety online to tell you how deep to plant.

When planting larger seeds, make a hole with your finger or a dibblet and pop them inside. For smaller seeds, sprinkle them on the surface and press them in gently or cover them with a light layer of soil.

Plant around two to three seeds per hole or cell, depending on what you are growing. This maximizes germination potential, ensuring you end up with the right amount of plants. As seedlings emerge, thin the weaker ones, leaving only one plant per cell.

Water

After sowing into damp soil, water again to saturate the top layer. It’s best to mist the soil with a spray bottle or use a watering can rather than a strong stream of water, as this can dislodge the seeds.

Keep the soil evenly moist but not soggy to encourage germination. Don’t let the soil dry out completely, as this can stunt growth early on. Always water gently to avoid disturbing the fragile new roots.

Cover

When you’re sowing in trays, you may want to cover the seedlings with a germination dome. This will keep moisture and warmth in, promoting growth. If you do go this route, remember to lift the cover daily to improve airflow and reduce potential mold growth.

Once the plants have sprouted and true leaves begin to appear, remove the cover and place the tray under grow lights or in direct sun.

Seedling Care

After sowing, check your trays regularly to keep the soil consistently moist. If you’re sowing in front of a window, rotate your trays so all sides get equal amounts of sunlight. Look out for seed-starting problems like damping off and improve airflow if needed.

Once your seedlings are a few inches tall, it’s time to move them into larger individual pots or into the garden, depending on the time of year. Give them time to adjust to their new environments by slowly exposing them to outdoor conditions over a week or two, a process known as hardening off. This limits the risk of shock after transplanting, ensuring your seed-starting efforts don’t go to waste.