Seed-Starting 101: 11 Tips to Get it Right
Seed starting doesn’t have to be complicated. A few simple steps can ensure prolific germination and vigorous early growth to start your season off right. Join organic farmer Logan Hailey for 11 straightforward seed-starting tips for beginners.
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Sowing seeds is one of the most exciting parts of starting a garden. Depending on your frost dates, this process can start in late winter or early spring and continue throughout the year if you want to practice succession planting. Regularly sowing ensures a consistent supply of new crops so you can harvest throughout your frost-free growing season.
Once you master the art and science of seed-starting, you’ll never need to buy expensive nursery starts again. Here are 11 pro tips I used as a commercial organic farmer to ensure perfect germination every time.
Tools and Supplies
The right seed-starting equipment is key to happy seedlings. Gather your materials and set up a dedicated nursery space to ensure that your baby plants enjoy an easy start to life.
The most essential tools and supplies include:
Containers
Cell trays and open flats are the most popular pots for sowing. You can also repurpose egg cartons, plastic tupperware, and nursery trays. Alternatively, use soil blocks or recycled paper pots for plastic-free options.
Soil or Soilless Medium
Seed-starting mixes usually contain well-drained materials like peat moss, compost, perlite, vermiculite, or coco coir. Ensure that water flows freely through the medium to prevent rotting.
Light
A south-facing window or greenhouse is the best way to ensure abundant light for germination. If you don’t have enough natural sunlight, supplemental grow lights are necessary. Most seedlings require at least 8-10 hours of light exposure per day.
Warmth
Keep containers in an area with ambient temperatures around 50-70°F (10-21°C), depending on the species. If the air is too cold for young sprouts, you may need to use a germination heating mat or build a cold frame.
Water
Consistent moisture is crucial for germination and early growth. You can use a standard watering can or opt for a rain wand hose attachment that delivers water with a delicate shower setting.
Labels
Garden stakes or popsicle sticks are useful for labeling your seed trays to track the varieties and sowing dates.
11 Beginner Tips for Seed-Starting Success
Sowing seeds can be intimidating as a beginner, especially if you’ve faced failed germination, rotten seedlings, or lackluster growth. However, the process can be significantly simplified once you understand the basics of how seeds sprout and what they need to grow into prolific garden crops.
Calculate the Right Seeding Date
The most important step of seed-starting begins before you ever put a seed in the ground—it’s all about timing! You can drastically improve your garden success by mastering the art and science of crop planning. Every crop has a different time frame and seasonality for its growth. Planting too early or too late can lead to delayed transplanting, failed harvests, and premature crop bolting or death.
Luckily, calculating the right sowing date is easy with this basic information from your seed packets and weather data:
First and Last Frost Date
The last expected spring frost is your best marker for when to sow seeds indoors or outside. It marks the final freezing temperatures of the spring, while the first frost date marks the expected initial freeze in the fall. Think of these as the bookends to your season. Both are calculated using historical weather data.
Days to Maturity
This is how many days it takes for a plant to grow from seed to maturity (whether it’s a harvestable vegetable, blooming flower, or ripe fruit).
Recommended Start Date
Most packets list a recommended sowing date e.g. “Start indoors 6-8 weeks before your last spring frost.”
To find the best time to sow a certain variety, grab a calendar and count backwards from your last frost date. For example, if your estimated last spring frost date is May 1 and you want to start ‘Lacinato’ dinosaur kale seeds indoors, you would sow the kale seeds around March 20 because the packet recommends starting indoors 4-6 weeks before transplanting outside. The seeds emerge in about 5-10 days and leaves should be ready to harvest 60 days after sowing (around May 19 in this example).
Use Quality Containers With Drainage
Quality containers make all the difference for seed-starting. I highly recommend that beginners choose durable, easy-to-transplant pots with large drainage holes, such as Epic 6-Cell Trays.
Side holes and large bottom holes keep the roots “air pruned,” which prevents them from winding around in circles. As a result, the seedling root balls grow extra healthy and easy to transplant. When it’s time to move them into the garden, all you need to do is push your finger up from the bottom hole and gently remove the seedling.
Crinkly disposable nursery trays can be much more problematic because they don’t have sufficient drainage and it’s more difficult to remove seedlings for transplanting. They are still a great budget-friendly option for sowing seeds indoors, but they may not last more than a season.
If you’d prefer a plastic-free option, try out a soil blocker tool. This tool creates compressed cubes of soil where you can sow seeds. Be sure to follow a special soil blocking recipe that keeps the container-less blocks together.
Choose a Well-Drained Soil Blend
If you’ve struggled to grow nursery-quality seedlings, it may be because you chose the wrong soil blend. Pulling dirt from the garden usually doesn’t cut it. Similarly, regular potting mix or raised bed soil blends are not ideal for seeds.
Indoor seed-starting calls for a fluffier, looser mix to facilitate germination and maintain consistent moisture without rotting the seeds. Soilless blends are particularly popular in nurseries because they are extra well-drained and prevent disease issues.
The easiest option is to purchase a bagged blend that is specifically formulated for seeds. Look for ingredients such as:
- Peat moss
- Compost
- Coco coir
- Vermiculite
- Perlite
Don’t Plant Too Deep or Too Shallow
The most common seed-starting mistake is sowing too deeply or too shallowly. As a general rule of thumb, you should only plant a seed at twice the depth of its largest dimension. So if a cucumber is about ½ inch wide, you should only plant it a maximum of one inch deep. However, avoid sowing shallowly on the surface unless the packet explicitly states that the species needs light to germinate.
Most vegetable seeds need soil-to-seed contact by burying them below the surface at the right depth. In contrast, native and wildflower species are often accustomed to germinating right on the surface.
Sowing depth makes more sense when you understand that a seed is basically a package with a baby plant and its food inside. The “package” is the endosperm, or outer shell. The baby plant is called the ovary, and the food is called endosperm.
Endosperm is primarily made of starchy compounds that came from the original mother plant. Each seed has a limited amount of endosperm starches that it uses to sustain growth until its leaves can begin photosynthesis above the soil surface.
The amount of endosperm depends on the species and ultimately determines how deep you should plant. For example, squash seeds are quite large and have lots of starch, which means they can be planted deeper in the soil because they have extra energy to grow their cotyledons (early leaves) upward.
In contrast, a basil seed is very tiny and may fail to germinate if you bury it too deep. Remember the “plant twice as deep as the seed size” rule and you’ll get the depth right every time.
Sow 2-3 Seeds Per Cell
Not every seedling in a cell tray will germinate, so it’s best to sow multiple seeds per cell. These extra plants act as an insurance policy so you don’t waste nursery space or soil. Different varieties may have unique germination rates, but it’s generally best to over-sow just in case some don’t sprout.
However, you must remember to thin the baby plants out, otherwise they will become overcrowded. It may seem like a waste to cut away seedlings you just worked so hard to sprout, but I’ll explain below why this step is integral to your seed-starting success.
Use a Heated Germination Mat
Heating mats are not always necessary, but they provide a mega boost for warm-weather crops like tomatoes, peppers, eggplants, squash, cucumbers, and basil. These seedlings can be slower to emerge in cold soils. Some may not germinate at all if the soil temperature is too cold.
A heating mat is a water-proof electric mat that you place underneath cell trays. It delivers warmth from the bottom of the container straight to the developing root zone of the plant. Even if the ambient air is only 60°F (16°C), this could raise the container temperature by 10°F or more, making the seeds germinate more rapidly and evenly. If your greenhouse or nursery area is fairly cool, this is a great way to enhance early plant growth without heating the entire space.
Ensure Bright Sunlight or Supplement
Light is crucial for all plants, but especially during the seedling stage. Seeds don’t need light to germinate, but once they sprout, they are very demanding. On average, most seedlings require 12-16+ hours of light exposure per day. This allows the young leaves to photosynthesize (create plant food from sunlight, water, and carbon dioxide), which fuels vigorous new growth.
If there isn’t enough light, your seedlings will appear spindly, leggy, pale yellow, and weak. They may arch like they’re reaching toward the window to get more sunshine. In this case, a supplemental growth light is essential to restoring normal growth. It’s helpful to lower the light a few inches above the developing leaves and raise it as they grow taller.
Maintain Airflow
A fan is an often overlooked piece of seed-starting equipment. If your nursery area doesn’t have sufficient airflow, the stagnant humidity around the base of the young plants can lead to a disease called damping off. Damping off is caused by fungus-like organisms that grow fluffy mold around the base of seedlings and eventually girdle the stems, causing the baby plants to collapse.
Fortunately, the disease is easy to prevent by maintaining open circulation. You can open a window for a breeze or keep a light fan blowing a few feet away from your trays. The added air can also strengthen stems to prepare them for windy weather.
Water Consistently
A developing baby of any species is especially needy when it comes to food and water. Plants are no different! These babies don’t yet have fully developed roots, so they can dehydrate rapidly. It’s vital to check seedlings at least once per day, and water thoroughly when the soil is dry. An easy rule of thumb is to irrigate until water pours out of the bottom drainage holes. Once the cell tray is saturated, stop watering.
Rain wands are my favorite tool for irrigating seedlings because they deliver water in a nice shower-like flow that isn’t too harsh on the developing leaves. This will ensure evenly distributed moisture without blasting young plants.
Overwatering can lead to rot and damping off disease, so be sure to check the soil moisture regularly. When growing in containers, it is easy to tell that the dirt is dry because it will shrink away from the edges of the plastic trays.
If it is overly wet, it may appear dark and soggy, or even grow green algae on the surface. In this case, you need to cut back on water and use a better drained soil blend with a lot of lightweight material like vermiculite or perlite. You can also practice bottom-watering by filling a bottom tray with water and allowing the seedlings to suck up the moisture through the drainage holes.
Thin Seedlings
Plants don’t want to be crammed together like sardines. It may seem like more plants yields more crops, but too many sprouts in one cell can actually cause unnecessary competition. For widely spaced crops like broccoli or squash, this can completely inhibit the crop from producing a reliable crop. Ironically, you can harvest far more vegetables or fruits by thinning away extra sprouts and keeping fewer plants that can grow to full size.
Overcrowding leads to stunted growth, poor leaf development, and higher risk for diseases like damping off. Luckily, it is very easy to thin your seedlings after germination. Needle-tip pruners or scissors are the best tools for the job, but you can also use your fingernails to pluck unwanted plants at the base.
Always be sure to thin away the weaklings once they are a few inches tall. Keep only one strong plant per cell to encourage robust growth.
Harden Off Before Planting
The final step of seed-starting is all about acclimation. You don’t want to throw a toddler out into the world to fend for themselves, so don’t do it to your plants either. If seedlings have been growing indoors with moderate temperatures and consistent water, they need time to adjust to harsher outdoor conditions. This period is called hardening off, and it prepares seedlings to be transplanted.
It’s best to harden off cell trays in a protected outdoor area such as a covered patio, porch, or partially shaded area near your greenhouse. Once the weather is sufficiently warm, move your trays to the protected area and gradually cut back on water.
Allow the plants to adjust for a few days to a week before transplanting in the ground. You may need to move them back indoors a few times if the nights get cold or they show signs of dramatic stress, like wilting or yellowing. Row fabric is a great way to buffer against extreme temperatures and protect from early pest damage before and after transplanting.
