How to Grow Peppers from Seed

Of all the vegetables that can be started indoors, pepper seeds seem to offer gardeners the most challenges. Each spring, we receive a number of emails from distressed gardeners who can’t figure out why their pepper seeds haven’t germinated. They planted them, watered, and waited and nothing happened. If you’ve arrived at this article in the same situation, don’t be discouraged. A lot of garden experiments require replication (my preferred word over “starting over”). This article is designed to give you a step-by-step guide on how to successfully start peppers from seed, every time.

So whether you’ve got some challenging chilis, stubborn sweet peppers, or bullheaded bell pepper seeds, grab a pencil—we’re about to coax those pepper seedlings out of the ground.

Factors That Affect Pepper Germination

There are a number of factors that will affect the germination rate of your pepper seeds. If you're reading this article with a packet of seeds in your hand and the scent of fresh soil permeating the air, I’m sure you will be tempted to scroll past this section and get down to business, but I assure you that a acquiring a little bit of understanding about pepper seed germination now will pay dividends in the future.

Seed Quality

It’s no surprise that the quality of the seed is the most important factor in determining the outcome of germination. Under the Federal Seed Act, the minimum germination rate for peppers sold in the United States is 55%. That leaves a lot of room for variation, and you will undoubtedly see differences in germination rates if you purchase seeds from different sources. Therefore, it is important that you start with high quality seeds from a reputable source. At Thresh Seed Co., our pepper seeds average around 90% germination, with above-standard rates maintained for 2-3 years thanks to our moisture and light-proof, resealable packaging.

Genetics

To some extent, the genetics of a variety will determine its potential for germination. We have observed, for example, that Fish pepper seeds tend to have an inherently lower germination rate. I suspect that this is due to the variegation within the maternal tissues of the developing fruit, though I've never investigated it fully. Whatever the case, you may sometimes find that a certain variety has an inherent limitation on germination rate.

Soil Temperature

Apart from the innate germination potential of the seed, the next most important factor influencing germination rates is soil temperature. The optimal soil temperature for pepper seed germination as prescribed by the Association of Official Seed Analysts (AOSA), is 85 degrees Fahrenheit. The following graph shows the average germination of pepper seeds over time using the AOSA protocol (green line). In the same graph, you can see how lowering the soil temperature increases the days to germination and decreases the overall germination rate.

The influence of soil temperature on the speed and rate of germination is worth noting because most gardeners do not have access to a temperature-controlled greenhouse, so they settle for the next best place—a window sill. A window, preferably south-facing, can be an excellent place to start your seeds. However, care should be taken to protect the germinating seeds from drafts and cold temperatures at night. Placing a seedling heat mat beneath the trays can vastly improve germination rates by keeping soil temps warm and stable. They can be purchased for as little as $15 online and they will last for years. Although a heat mat will improve germination of most vegetable seeds, we think they are especially critical for starting peppers and we recommend them to all of our customers who are wanting to grow their own peppers.

Water

Over-watering is the most common mistake when starting peppers, or any seed for that matter. When it comes to peppers and water, less is more. Watering the plants cools the soil and invites fungal growth. Additionally, most tap water contains small microbes that can grow in the soil. As peppers are somewhat slow to germinate, any competition with fungi or other microbes hurts the seeds' chances of germination. Furthermore, certain fungi can cause “damping off” a fungal disease that is often deadly for seedlings.

Soil type

Shopping for soil can be confusing. There are dozens of products on the shelf, and the labeling is often ambiguous. In general, avoid anything labeled Top Soil or Garden Soil. The mixture you’re looking for is actually soil-less—even though it may still be labeled as “soil.” Confusing, I know.

When in doubt, read the ingredients. Avoid mixes that contain compost, manure, or natural soil, as these are rarely sterile and can introduce fungi or other microbes that interfere with germination. Instead, look for blends made from peat, bark or coconut coir, and perlite or vermiculite. If you’re lucky enough to have a good local garden center, you may even find a product labeled seed starting mix, which is exactly what you want. These mixes are sterile, finely screened, and often include wetting agents that help water penetrate evenly rather than running off the surface.

If you want a deeper dive into what makes a good seed-starting medium (and how to choose one with confidence), I’ve written a full guide on how to select the best soil for starting your seeds, which goes into more detail.

The last thing to look for in a soil mix is calcium. Calcium has been shown to improve germination under various stress conditions and, importantly, it can’t be added effectively later in liquid form. Make sure your mix includes a calcium source from the start—most do, usually in the form of lime (calcium carbonate) or dolomite lime. Less common sources include oyster shell, ground marble, or gypsum.

How to Grow Peppers from Seed

Okay, we're ready to get started. Time to gather up your supplies. Below is a list of the items you will need. If any of them sound surprising, refer to the section above.

You Will Need:

• Seed trays and dividers
• Clear plastic dome
• Seedling heat mat
• Sterile seed starting mix
• Watering can
• Pepper seeds
• Planting stakes for labeling
• Natural or artificial light source

Step by Step Instructions:

Step 1.  Sterilize trays and dividers

If you are re-using old trays or dividers, be sure to sterilize them by scrubbing with hot, soapy water. Soil that has been left in the trays could be harboring soil pathogens that may threaten your fragile seedlings.

Step 2. Fill trays with soil mix

Use a sterile, soilless starting mix (see section above). Pile the soil in the center of the tray. Break up the clumps and remove any large chunks of bark or wood that may be in the soil. Smooth the soil out to the edges until all of the cells are filled and the soil level is flush with the tops of the containers. The level will decrease slightly after watering.

Step 3. Pre-wet the soil and allow it to drain

If you are working inside, it may be best to do this outdoors. You want to put a good bit of water through the soil to make sure it is completely moistened. Allow the soil to drain for at least 15 minutes. For best results, repeat.

Step 4. Make an indentation in the soil

Using your finger, make a ¼ inch indentation in the soil. For reference, ¼ inch is roughly half-way to your first knuckle. If you have a good soil mix and optimal moisture, your finger should press easily into the soil, like pushing on a soft sponge, however the soil should not rebound when you remove your finger.

Step 5. Sow the seeds and cover

Sow 1-2 seeds into each hole. You can either pinch in the soil around the hole or add additional fresh mix over the top. If you are planting multiple varieties, label each with a stake or popsicle stick. Also include the sowing date.

Step 6. Water once more

Once again, you want to soak the trays. Water until you can see water draining from the bottom and then water a few seconds longer. Allow the tray to drain completely. You do not want any water sitting in the bottom of the tray.

Step 7. Place the tray on a grower's heat mat

Don't forget to plug in the mat. If your mat has a probe, place it in the soil and set the thermostat to 85 degrees. Simple mats without this feature work just fine too.

Step 8. Place on a heat mat and cover with a plastic dome

Using a dome helps to keep the soil warm while minimizing the need for watering. It also protects young seedlings from cold air and drafts.

Step 9. Watch and wait

I know, it's hard. Keep in mind that you likely will not see any sprouts for a week or two. Many gardeners sow tomatoes and peppers at the same time and begin to get anxious when they see tomatoes germinating after just a few days. Try to be patient, peppers just take a little longer.

This is the biggest secret to starting pepper seeds: Do not water the plants for at least two weeks. Every few days, you can tap the top of the lid to redistribute the water that has condensed inside and lift the corner to let in a bit of fresh air. If the temperature in the growing room gets particularly hot, for example if you are using a sunroom, prop up the corner of the lid using a pencil. Always close the lid at night, though. This will keep the soil warm and the seeds growing throughout the cooler nighttime hours.

Okay, they're up! Now what?

Well done! Congratulations, the hardest part is over. After most of the seeds have germinated, you can remove the lid and unplug the heat mat. The seedlings will need cooler temperatures now--room temperature is perfect. If temperatures are too high, the plants will grow too quickly, causing them to become soft and tender, thus making their transition to outdoor living more perilous. Keep the seedlings under light or near a south-facing window. Plants that do not get enough light will stretch looking for it, causing them to become leggy and fragile.

When to Water Pepper Seedlings

Wait—don’t water yet. If you’ve just removed the dome, chances are the seedlings still have plenty of moisture available. Many peppers trace their origins to arid and semi-arid regions of central Mexico, where they evolved to tolerate extended dry periods. Small-fruited, wild types like Pequin pepper seeds, including close relatives such as Chiltepin, are a good reminder of this—these plants resent constantly wet soil.

Rather than watering on a schedule, watch your trays and plants for cues. Along the outer edges of the tray, the soil may begin to pull away from the container walls, or the leaves may just start to lose their perk. When you see those signs, it’s time to water. If you’re going to be away for several hours and know the plants will get thirsty, watering preemptively is fine. The goal is to give the plants enough water while allowing the soil surface to dry between waterings. If the surface stays wet, algae and fungi can begin to grow, forming a crust that prevents water from absorbing into the soil.

Despite best efforts, some algal or fungal growth is common. If it becomes severe enough that water runs off the surface and down the sides of the container without soaking in, it’s time to intervene. Gently scrape the soil surface with a fork to break up the crust—just enough to open a pathway for water, without disturbing the roots below.

When to Fertilize Peppers

Seeds are amazing creations. Inside each one is the beginnings of a plant-- a root, a shoot and the first few leaves—as well as enough food to get them off to a good start. Therefore, you do not need to fertilize your seedlings at first. If fact, doing so may be of more benefit to soil pathogens than it is to the seedling. Should you choose to fertilize your seedlings, it is best to wait until the plants are large enough to resist fungal diseases-- this is usually once the first set of true leaves is fully emerged. We seldom fertilize our seedlings unless we notice that the leaves are getting a bit pale. At this point, we'll give them a half-dose of liquid fertilizer and see how they perform. If their condition improves, we'll give them another half-dose a week later.

Woohoo, You Did It!

If you made it this far, congratulations—your seedlings are well on their way. Pepper plants tend to grow slowly during the first month, so don’t be alarmed if progress feels modest at first. They’re busy establishing roots and getting ready to take off once conditions improve.

Until it’s time to move them outdoors, the goal is simple: keep your seedlings healthy, warm, and evenly watered. And if you’re still deciding what to grow next, feel free to explore our collection of heirloom pepper seeds, where you’ll find a wide range of varieties—from classic bells to heat-loving chilis—ready for the garden.