Starting Pepper Plants Indoors


Most climates in the U.S. don’t have a long growing season so unless you live in a zone with short winters, starting pepper plants indoors pre-season is essential. In this article we’ll cover basic seed starting information and some things that are specific to peppers. Here’s a summary version on how to start peppers seeds indoors.

Ideal Time for Starting Pepper Plants Indoors

The standard recommendation is to germinate pepper seeds at least eight weeks before your last frost date. However, if you live in a northern climate or want to maximize your harvest you should start your pepper seeds even sooner. We are in Zone 6b and sow our peppers plants in early February with a last frost date, usually in mid-May.

What Type of Soil for Starting Pepper Plants Indoors?

Generally speaking, the seed starting mix should be mostly devoid of nutrients. There is enough nutrition stored within the seed to sustain the plant for the first few weeks after germination. The best seed starting mixes will provide good drainage. Without good drainage the roots will not be properly aerated. Additionally, too much moisture will lead to dampening off, the plant rotting at soil level.

You can either purchase seed starting soil or mix your own. If you’re only growing a small amount of pepper plants it would probably just be easier to just buy a bag of something like Burpee Organic seed starting mix.

When starting a lot of seeds, you should consider making your own bulk seed starting mix. Just mix equal parts of sphagnum moss (or coconut coir), vermiculite, and perlite. Sphagnum moss (or coconut coir) and vermiculite will hold moisture in the mix while the perlite will prevent compacting and allow proper drainage.

Personally, we prefer to use the coconut coir instead of sphagnum moss. In recent years sphagnum moss has come under fire for being an unsustainable resource but it’s not the reason we choose not to use it.

Some of the reasons we prefer coconut coir are:

  • Sphagnum moss can be hydrophobic, reject water rather than absorb it. If allowed to completely dry out the water will simply run off without being properly absorbed. It is possible to use add surfactant to your water source to remedy this problem.
  • Coconut coir is much better at absorbing water, even if allowed to completely dry out, and requires no surfactant. When watering coconut coir the excess water will drain away but retain the proper ratio of moisture and aeration.
  • Sphagnum moss can be too acidic, the ideal pH for most plants is between 5.5 and 6.5 for proper nutrient uptake. Sphagnum moss can have a pH as low as 3 is not amended with lime.

Downsides to the coconut coir:

  • It costs more than sphagnum moss, but not by much. Coconut coir can be purchased in dehydrated compressed blocks which makes it easy to get shipped to your home. An 11lb compressed block of coconut coir will fill a wheelbarrow once rehydrated which brings it more in line with the price to the sphagnum moss.
  • May need to be buffered depending on the source. This means soaking the coconut coir with a solution containing nitrogen and magnesium such as Cal-Mag. If buffering isn’t performed the coconut coir will absorb the nitrogen and magnesium from the fertilizer the first few times you apply it. This could lead to yellowing of the plants and stunted growth. Always verify from the supplier whether the coconut coir you’re purchasing has been “buffered”, not just “rinsed”.

That said we still feel that coconut coir is a better choice due to its superior drainage and moisture retaining properties.

Sowing the Plants Indoors

starting pepper plants indoors seedlings

The most common containers for starting pepper plants indoors are seed starting trays. You can purchase a tray with all the cell packs and a humidity dome as a kit. Trays are ideal if starting a lot of seeds. Standard 10″ x 20″ trays will usually hold a total of 72 seedlings per tray in a small space.

Be sure and moisten your seed starting mix before filling your cell packs. The seed starting mix should be just moist enough to squeeze a few drops of water out of a handful. If the soil is too wet you risk the seeds rotting in the soil. Once the starting soil is moistened, fill the cells taking care to pack the soil lightly.

Even in optimal conditions not all seeds will germinate. As such, you should consider planting two seeds per cell to ensure you don’t end up with vacancies. If both sprout you can sever the weaker seedling at a later time. To plant the seeds, start by pressing 1/4″ divots in each cell. You can use the eraser end of a pencil to do this or just your fingertip. Drop two seeds into each divot and cover the seeds with additional soil. Just make sure the seeds remain at a depth of no more than a 1/4″. Once all your seeds are planted cover the tray with the humidity dome to ensure the soil doesn’t dry out.

You should remove the humidity dome every couple of days and check the moisture level. If you notice the soil is drying out you can spray the soil with a water bottle but don’t overwater. Moisture droplets on the inside of the humidity dome usually indicate enough moisture. Cells around the perimeter tend to dry out sooner than those in the middle of the tray.

Germination Times for Peppers Plants Started Indoors

Pepper seeds will take at least a week to germinate even when kept at the ideal temperature. In the case of hot and super-hot peppers, two weeks is a more realistic outlook. Be sure and factor this timeframe into your preseason planning. It is recommended to keep the seed trays at a minimum of 80F for optimal germination when starting pepper seeds indoors.

The easiest way to warm your seed trays would be to purchase a seedling heat mat with a temperature controller. Never use a heat mat without the temperature controller. The heat mats are usually made to fit perfectly under the standard 10″ x 20″ trays. If you’re germinating the seeds in a cool area such as a basement it may be difficult to maintain the proper temperature even with a heat mat. Check out our video on how to insulate your seed trays for optimal germination.

It is unlikely that all seedlings will sprout the same day so it’s recommended to leave the humidity dome over the trays until at least one per cell has popped up. Once some of the seedlings are above soil make sure not to allow too much moisture under the dome. There are some humidity domes on the market with adjustable vents but propping the lid up a quarter inch on one side serves the same purpose. This will allow excess moisture to escape.

If all your seedlings have sprouted you t. You might also choose to remove them completely from the heat mat. This will depend on the ambient temperature of your grow area. In a cool basement or similar you may be better off continuing the use of the heat mat. Just be sure and dial down the temperature to 68 or 70F. Too much heat is not good for the roots so monitor for signs of distress.

pepper plants starting indoors seedling helmeting

As the seeds break through the soil, some of them have the seed still attached to the top. This is known as “helmeting”. Usually, the seedling will be able to recover and shed the seed. Sometimes the helmet doesn’t allow any exposure of leaves, a much more dire situation. Helmeting is usually caused by low humidity. The seed shell dried out and is less pliable. You can try moistening the shell with a spray bottle of water. Attempting to remove the seed shell usually results in the top of the seedling and cotyledons breaking off. Although with some finesse and a couple pairs of tweezers you may be able to pull the two halves of the seed apart. If the top of the seedling with cotyledons breaks off it will not recover.

Lighting for the Pepper Seedlings

Starting pepper seeds indoors will require supplemental light. The seed trays don’t require light until the pepper seedlings sprout. Once they break through the ground, they should be given light as soon as possible to prevent them from stretching. There’s really no way to know when the seeds will sprout. It may be easier to just keep the lights on over the trays even before they’ve sprouted.

Some people simply use fluorescent or LED shop lights to grow their seedlings. However, for maximum growth rates you’ll need stronger grow lights. We recommend a good T5 fluorescent fixture or strong LED grow light.

NOTE: Don’t attempt to grow your pepper seedlings in a windowsill, even a south facing window. Your pepper seedlings will inevitably stretch out (get leggy). They’ll also lean to the side as they try to reach adequate light.

T5 Grow Lights

These are the type fixtures we have been using for years. They don’t put out much heat and can be kept within inches of the seedlings. The T5 grow light fixtures can be purchased in either 24″ or 48″ length. We use the 24″ fixtures for versatility. Probably the only downfall to the T5 grow lights is that the bulbs need to be replaced periodically. Not frequently but they will eventually need to be changed. This can add a little extra cost to your setup. Most bulb manufacturers recommend changing the bulbs every 9-12 months if the light is used 8-12 hours a day. Assuming you only use the lights for a few months every spring, you wouldn’t need to change bulbs for several years. We recommend bulbs with a spectrum of 6500k. This gives a balance of red and blue light waves and simply looks white. Some fixtures can be purchased with bulbs included such as these T5 grow lights on Amazon.

LED Grow Lights

In recent years LED grow lights have made great strides. New fixtures on the market provide a nice bright light with a low operating cost. Quality LED fixtures are usually a more expensive initial investment than T5’s. However, there is no need to ever replace bulbs for the life of the fixture. However, there is a lot of disputes over whether they are superior to the T5 fixtures. Many hobbyists believe they have better growth from T5 grow lights vs. LED. Be sure and check the LED manufacturers instruction for the recommended distance from the seedlings.

Starting Pepper Plants Indoors – Life After Sprouting

With the seedlings sprouting and living under the grow lights you’ll just need to maintain them. There’s really not much you need to do for the first several weeks. Mainly just to prevent them from drying out. You’ll probably notice that the first set of leaves don’t look like the leaves of a pepper plant. The first set of leaves are called cotyledons. The second set of leaves that grow will be the “first true leaves”.

Watering the Pepper Seedlings

It’s worth mentioning that overwatering is as bad as underwatering. Sometimes the top of the soil will be dry but still be moist at the depth of the roots. The best way to know if watering is necessary would be to familiarize yourself with the weight of the cell pack when it’s properly watered. You’ll notice that the cell pack is much lighter when in need of water.

The best way to water the pepper seedlings is bottom watering. This means adding water to the tray. The cells will absorb water through the holes in the bottom. Generally speaking, adding about a half inch of water to the tray should sufficiently moisten all 72 cells. Of course, less is more. Start with a small amount of water the first few times you water to see what your seedlings need; you can always add more water.

Fertilizing the Seedlings

The pepper seedlings will take about two weeks to grow their first set of true leaves. No fertilization is needed until the true leaves appear. The seedlings had all the nutrition they needed to sustain them for the first few weeks. These nutrients are packed right into the seed. Think of it like the yolk of an egg.

Two weeks after starting pepper plants indoors it will be necessary to provide fertilizer to the seedlings. They will have exhausted the nutrients from the seed and the seed starting mix is mostly devoid of nutrients. Choosing a fertilizer can be a little tricky. On fertilizer packages you’ll see a string of 3 numbers (example 3-4-5). Those numbers represent the N-P-K (nitrogen, phosphorus, potassium). We recommend trying to find a balanced water-soluble fertilizer such as 5-5-5 or 10-10-10. It’s not always easy to find fertilizer with equal numbers. Any reputable brand of tomato and pepper fertilizer should work.

The first few times you fertilize you should only use quarter strength fertilizer. Don’t fertilize every time you water, every two weeks should suffice. If the leaves are a pale green, it could be from overwatering or not enough nutrients. Make sure you’re not overwatering first before you step up with the nutrients. If you’re sure the problem isn’t overwatering then increase the concentration of your fertilizer. You’ll also need to increase the strength of the fertilizer as the seedlings get larger and grow more leaves.

Starting Pepper Plants Indoors – Transplanting

When starting pepper plants indoors you’ll eventually need to transplant them seedlings into larger containers. After several weeks in the cell packs, you’ll start seeing roots growing out the bottom holes. Pinch the bottom of the cell to loosen the soil. Then simply turn the cell pack upside down and finesse it out, don’t pull the seedling out by the stem.

If you see lots of roots that are starting to wrap around the cell transplant to a 4″ pot. If you see roots out the bottom of the cell but they’re not wrapping around you could still transplant them. You’ll just need to treat the seedlings a little more delicately.

When transplanting from the cell pack to the larger container it’s time to add some organic matter into the soil. To do this, simply add compost to some of your original seed starting mix. Use a ratio of about 1/3 compost to 2/3 of the seed starting mix. As you transplant the seedlings be sure not to bury them deeper than they were in the previous container. You should also be safe to use full strength fertilizer at this point as well.

Red Solo Cups

Most pepper enthusiasts these days prefer red solo cups for the second stage container. They hold about the same volume of soil as a 3 or 4″ flower pot and are less expensive. If using the solo cups, you’ll need to add drain holes. We use a soldering pen to melt holes in ours. It’s fast and no cracking of the plastic which will occur when using a drill bit.

The solo cups can be taken a step further using what’s known as the double cup method. Using the double cup method is simple. Transplant your seedling into one cup with drain holes. Then place that cup into a second cup that has no holes. This creates a void at the bottom between cups allowing you to bottom water. Some solo cups fit together without leaving a void. If so, you can place a few pebbles in between the cups to prevent them from fitting tightly together. Ideally you want about a half inch void between cups.

Caring for the Pepper Plants

The pepper seedlings can remain in the solo cups or 4″ pots until planting in the garden. From here out it’s just a waiting game. Give them water as needed. Give them some fertilizer every couple of weeks, and adjust the height of your grow lights over your pepper plants as they get taller.

Keep an eye out for plants stretching. All varieties of pepper have different growing habits. Although, generally speaking, as the plants grow you should only have about an inch of internodal space. Internodal space is the distance between sets of leaves. If the plants start stretching it’s a lighting issue. Either your light isn’t bright enough or it’s too far from your plants.

Starting pepper seeds indoors 8-10 weeks before the last frost should result in plants at least 6″ tall when they’re ready to move outdoors. I start my seeds in the first week of February. By spring they are usually 8-12″ tall when transplanting into the garden, depending on the variety.

When it’s time to transplant the seedlings outdoors you’ll need to harden them off. This means acclimating them to full sunlight. Even if you used powerful grow lights, they will still burn up under the UV rays of the sun. Start will full shade for the first few days. Gradually give them more and more direct sunlight over a period of a couple weeks. If you notice brown spots on the leaves or shriveling this is a sign of sun scorch.

Hopefully you found some useful info on this page. If you have any questions feel free to post them in the comment section.

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