How to Grow Seeds Indoors – 8 Big Tips to Know

Establishing plants from seeds is often necessary to enjoy healthy plants that you can transfer outdoors. And the best way to plant seeds is planting seeds indoors.

A major benefit of starting seeds indoors is that you don’t have to wait for the weather to turn warm before you can grow plants. 

And germinating seeds indoors means that by spring, you already have plants ready to go into the ground, giving you a head start on your growing season. 

I used to be the person that would plant my seeds directly into the ground and then wait with starry eyes for signs of buds while my neighbors were already enjoying gorgeous blooms.

But then, as I started my career as a gardening expert several years ago, I realized the error of my ways! And now, I teach others how to grow seeds indoors.

Table of Contents

There are many benefits to going the route of germinating seeds indoors. First, you get better control of when your flowers bloom, meaning you can have a rival garden earlier in the season. 

And it’s more affordable than buying nursery or commercial plants or seedlings. Plus, you have more options for what to grow and how many of each species.

We won’t even mention the health benefits – physical and psychological. Watching seeds grow from nothing can be an excellent way to zen and be amazed at the beauty of life.

Growing seeds indoors can vary by budget, experience level, available time, location, and materials. 

Making a detailed plan can keep you organized, get your seeds to emerge at the right time, and save you time and stress.

Making a List – What to Grow?

The first thing to schedule is what plants you want to grow and when. Different seeds will need to be planted at varying times and conditions. 

Make a list or use a spreadsheet tool like  Microsoft Excel or Google Sheets to keep detailed notes of your seeds. For example, you can include the following information for easier indoor seed growing.

  • Plant name
  • Indoor planting time
  • Pre-planting preparations
  • Growing conditions
  • Germination time
  • Recommended transplanting time

Should I Schedule the Germination Cycle?

Some people like to keep two lists. One for planning your indoor seed garden, including how to care for your plants, and another that records the information once you’ve planted your seeds. This schedule would track the germination cycle of each plant. For this chart, you’d include details like:

Schedule of Germination Cycle

For your second list, it helps to keep track of the estimated last frost date in your area. This data is crucial for knowing when to start seeds indoors. 

Search your location with the Plantmaps website or ask your local nurseries. Remember that this number is not an actual date but a reference point and can vary by situation.

How to Determine the Ideal Indoor Sowing Needs?

When sowing seeds indoors, you must know each plant’s specific growth time. Planting all your seeds simultaneously can result in a poor, underproducing garden. 

You’ll need to do some math to determine when to start your seeds indoors. So, once you know your area’s estimated last frost date, you’ll count backward by the plant’s germination period.

Most seed packets have a chart on the back outlining the plant’s germination period. Many charts also provide indoor sowing and outdoor transplanting instructions. 

Here is a rough estimate of some general guidelines by vegetable plant:

Plant Germination time period

However, many plants won’t require you to start them indoors with grow lights. 

Is Necessary to Record Keep?

If you keep detailed records of your plants, you have a higher outcome of successfully sowing your plants indoors. 

Each time you sow seeds indoors, add the information into your spreadsheet, print-out, or other record keepers. 

The best thing about making notes for your plants (especially if you’re absent-minded like me) is knowing when to do each step. 

And you can keep a copy of all your records to refer to in future seasons to compare your technique. If this interests you, consider adding extra columns to your documents.

Next to the seed germination column, you can add the actual germination date. And then do the same for actual transplantation outdoors. Again, these details give you better data than estimated info.

Did it take longer than the estimated time for your seedlings to emerge, or was it faster? What was the comparison between the estimated and transplant time?

Which Location Is Best?

Although we’re discussing the technique of growing seeds indoors, you’ll need to consider your outside situation briefly. If you’re not growing your plants outdoors, you can skip to the next step.

It’s a good idea to plan your outdoor growing site. When you map out your beds, it can estimate how many seedlings you’ll need to fill each space.

When picking the ideal site for each plant, consider how much space each needs – height and width? Overcrowding your plants can cause negative growth and might encourage disease. 

If you’re growing plants in outdoor containers, you’ll need to estimate the size of the base the plants will need. 

And will they need support to grow to their full height, such as a trellis, post, or stake? And are you choosing a spot that gets enough light – not too much or too little sun? These factors might affect where you sow your seedlings outdoors.

What Supplies Are Recommended?

Once you’ve mapped out your indoor seed growth plans, it’s time for the next step – shopping. 

Your success at germinating seeds indoors starts with preparing the right supplies. There are several things you’ll need to grow seeds inside.  

Most of these things are inexpensive to buy at your local garden center or online. But you can also DIY several options for a more self-sustaining approach.

Your seeds require a container to grow, referred to as seedling trays. You may also hear them called cell trays or seed starting pots. 

seed tray near window

There are many different types of trays available commercially. Popular ways to grow your seeds indoors include peat pots, pellets, and plug trays. 

For homemade options, you can make pots from recycled newspapers, coffee filters, egg crates, yogurt cups, or Dixie cups. 

Whatever container you choose should have a few drainage holes poked into the bottom. An awl or a nail makes the appropriate size shape.

These seed pots will need to go into a seed tray – commercially known as a 1020 plant tray. This container should not have holes so it can hold water. 

Newspaper Seed Pods

To DIY newspaper pots, you’ll need a stack of newspapers, small cans, and scissors. A six-oz can – like tomato paste – or shot glass is the appropriate size and shape for seedlings. 

Place two newspaper pieces together (creating four sheets). Then cut the newspaper into thirds, long-wise. Then roll the newspaper around the can by pushing the can away from you.

Cut each piece of newspaper into 3rds

Be sure to leave a 1″ overhang off the edge. And keep the roll loose so you can slide it off the can. Finally, fold the edges over firmly around the can. 

Then flip the can over and give it a firm press to flatten the folds. Finally, pull the can out, and your biodegradable pot is done. 

completed newspaper seed pots

Coffee Filter Seed Pots

You can also make compostable seed pots with coffee filters – or paper towels. And you’ll also need ziplock bags. 

Start by sizing your coffee filters to fit the number of seeds you’ll be germinating. Then wet the coffee filters, wringing out any loose water. It should be damp but not drenched and dripping.

Add your seeds to the bottom of the paper, leaving about an inch of space between each for root growth. Then sandwich the seeds with the top layer of the filter. 

Transfer the seed-filled filters carefully to the ziplock bag. Storing the bags without air in them is great for saving space. 

But filling them with air can produce similar conditions to the greenhouse effect. So before sealing them completely, stick a straw through a small opening in the seal and blow air inside.

Keep your baggies in a warm, humid area; bathrooms and laundry rooms are great. But the seeds shouldn’t get heated. 

Within a few days, the seeds should sprout radicles – the main root that forms from the plant’s embryo. You can transplant the seedling into a potting mix when the root is one to two inches long.

Egg Cartons As Seed Pots

While you can use styrofoam or cardboard egg cartons, the cardboard type is biodegradable. Therefore, you can plant these directly into the garden once the seedlings grow. 

Start by cutting the egg carton apart into individual pods. Then poke holes into each one before placing them onto a tray. Make sure the container is solid enough to collect draining water.

egg carton seed pots
Don’t forget to separate the individual egg pods BEFORE adding the soil.

For styrofoam egg cards, remove the lid from the egg holder. Then add drainage holes to each pod. Finally, stack the newly converted seed pod section into the top, which becomes a tray. 

Fill each egg carton with potting medium, and add the seeds and water. Then cover with plastic wrap, a plastic dome, cellophane, or a plastic dome. 

Remove the plastic once the seeds germinate and bring the pods into the light. 

The Best Soil for Seeds

Choosing the right growing medium is an often overlooked step for beginner gardeners. It’s better to alter the soil you use to meet your plant’s needs. But, wait, there are different types of soil? 

Who knew there was so much to learn about growing plants? They make it look as simple as putting a seed into a hole in the ground and adding water on the TV. No explanation is necessary!

But as with most things we discover as adults, it’s not that simple.

As weird as it may sound, seeds require sterile soil. You’ll also want to pick a medium that drains well. Organic soil and soilless soil are also safe, as long as they stay sterile. Soilless soil is primarily made up of sphagnum moss with additions such as bark, coir, perlite, vermiculite, and/or compost. It can work better than regular garden soil as it allows for more drainage, is more sterile, and does not become as compact  over time.

Best Soil Type for Seeds

The ideal soil will be light and fluffy so it can dry out quickly. All-purpose and multipurpose mixes generally work for big seeds. 

While a seed-starting mix is better for smaller start seeds like most flowers. And this type has lower nutrients. But make sure your medium is peat-free if you’re eco-conscious.

You can even use a soilless mix specifically designed for seed starting. The loose, fine-grain consistency and lightness allow baby roots to channel through the dirt and provide nutrients. 

Potting Soil (Mix) vs. Seed Starting Soilless 

What is the difference between a seed starting mix and a standard potting soil?

Standard potting dirt is a mix of topsoil – regular dirt – vermiculite, bark, humus, perlite, manure, peat, and fertilizers. This mixture can be too dense and heavy for seed growth.

Potting mix is a soilless type of potting soil. But it’s also not as suitable for establishing seeds. Both types have chunky pieces and a coarser texture with poor drainage and higher nutrients.

But when you pick the right potting medium, you can leave your seedlings in the pot when you plant it in the ground. Potting soil and mix will require repotting your seedlings during transfer.

How to Make Seed Starter Mix

DIY a soilless seed starting mix with three basic organic components. This type of starting mix does not have any synthetics or fertilizers.

First, you’ll need sphagnum peat moss. Do not confuse this moss with the type of moss liner used for baskets, which is more fibrous and coarser. Finer fibers provide better water retention.

sphagnum peat moss
Sphagnum peat moss

If you prefer to avoid peat moss, a suitable alternative is coco coir. It shares similarities to peat, including texture, appearance, and moisture absorption. This material is coconut shell fibers. 

coco coir close up
Coco coir

The next ingredient to include is perlite. This material looks like the small white popcorn texture commonly seen on ceilings. The super lightweight volcanic glass adds aeration and drainage.

perlite close up

Then you’ll need vermiculite, a brown granular micaceous mineral that absorbs water. Adding this material helps keep your soilless mix wet.

vermiculite up close

Preparing Soilless Starting Mix

Making a basic seed starter mix is quick and easy. You’ll need one part of each ingredient – perlite, vermiculite, and sphagnum peat moss or coco coir.

A part measurement is a generic term that can refer to anything you use to distribute your components evenly. For example, you can use a scoop, a bag, a bucket, or a bowl. Just keep it consistent.

Mix all three ingredients into a clean bucket or tub. Then pour water over the mixture to saturate it. Next, use a trowel or your hand to stir the ingredients to moisten the mix. 

Do not make your mix soggy. You’ve added too much water if it feels like a wrong-out sponge. Instead, watch the mixture as you add water. Once it stops absorbing liquid, stop adding.

Lighting Requirements for Seeds

Next, you’ll need to decide on the lighting source for your indoor seed germination. Most plants require you to give seeds 12 to 16 hours of supplemental lighting daily. 

Without enough light, your seeds will turn into vulnerable gangly pale seedlings. But your seeds will need short periods of darkness too.

One schedule is to turn the lights on when you wake up in the mornings. And then turn them off before you go to bed. Another option is to set your lights up on a timer.

The best choice for encouraging seedling growth is full-spectrum grow lights. The lighting can be fluorescent or LED bulbs. 

Types of Grow Lights for Indoor Seed Growth

Grow lights are a form of electric lighting that mimics the process of natural sunlight. This light encourages photosynthesis – making oxygen, water, and light into energy.

Grow lights are better as the lighting for seeds versus regular bulbs. A grow light bulb has all the colors on the spectrum – red, yellow, blue, violet – similar to natural sunlight.

Fluorescent bulbs are a budget-friendly way to germinate seeds indoors. This bulb type is also suitable for leafy greens and herbs you grow indoors. 

You can get these bulbs in most sizes; the added benefit is they don’t heat up. Fluorescents can be full-spectrum, or you can use warm and cool bulbs to simulate full spectrum.

T12 or T8 bulbs are okay, but the best growth comes from high output T5 fluorescents or LEDs.

LED (Light Emitting Diode) lights also come in full spectrums and work for indoor seeds and plants. However, these bulbs are more expensive than fluorescents. 

But they last longer and they use up less energy. And even better, they put out a better source of the light spectrum.  

Light Bulb Placement

Picking your light bulbs isn’t the only task you have to perform for your plant’s lighting needs. You also need to determine how to position your light bulbs. 

Many home gardeners like to use a grow light shelving unit to position the bulbs securely. However, there are several suitable commercial options if you have the extra money.

But if you’re budget-conscious, it’s possible to go a more affordable option and DIY a light stand. Your lights should hang 2″ to 3″ above the dirt. Adjust the position as the seedlings grow.

Heat Mats for Growing Seeds

While the grow lights will provide your seeds with heat from above, you can also warm the pots underneath. A heat mat can speed up the seed germination process.

Heating mats will keep your seeds warm to the ideal temperature of 70 to 80 degrees F. The thin, reusable mat is waterproof and can raise the soil temperature by around 20 degrees F. 

For more advanced options, there are heat mats with thermostats that let you monitor the soil’s temperature. You can also use a soil thermometer for constant monitoring. 

Heat mats also come in different sizes. The size appropriate for your indoor seed growing will depend on how many seeds you germinate.

  • 10″ x 20″ mat

If you’re trying to germinate mixed or a single flower species at the same temperature, you can use a 10″ x 20″ mat. 

This size is appropriate for a single 1020 flat. Your flat can contain insert pots in cells of 32, 50, 72, 128, or 200. 

  • 20″ x 20″

Double the size means double the quantity of seeds the mat can warm. For example, this size can cover two 1020-cell tray flats for seeds with the same temperature needs.

  • 20″ x 48″ 

This larger-size heat mat can warm four 1020-sized flats full of cell inserts. It’s most common to use this mat for commercial and large-scale seed germination.

The operation of a heat mat is simple. First, plug the mat into an outlet and let it warm your plants up to 10 degrees higher than the ambient temperature in the room.   

There are even mats you can connect to create an entire heating system, run vertically or horizontally. But do not exceed ten mats per chain.

Mister and Watering Can  

Keeping your soil adequately moist is crucial to germinating seeds indoors successfully. A spray bottle – or a mister – can be the best way to dampen the dirt without drowning it.

After the seedlings have gotten a bit of height and sturdiness, you can switch to using a watering can to water the plants. Pick one with a rain nozzle that dispels the water softly.

Another option is to use the bottom-up watering method. This technique is as simple as filling the solid tray underneath your cells with one to two inches of water. 

Avoid using cold water for your plants. Instead, fill your container with tap water. Then let it sit for a few hours to warm up to room temperature. You can even leave it sitting open for a day.

Plant Labels

Labeling your seeds is pretty important if you want to keep track of what you’ve planted. But unfortunately, the more sources you produce, the harder it can be to remember which cells belong to what species.

You might have hopes of being able to identify the different seedlings once they grow. But many seedlings are similar-looking when they first shoot out of the dirt.

Adding labels can not just help you know what plants are in each cell. But it can also help you know if your plants aren’t growing as expected or if you’re not giving them the right care.

We’re not recommending you spend a fortune on expensive plant labels or buy a fancy labeling machine. 

You can DIY labels using any items you have around your home. For example, if you have toothpicks and sticker labels, you can make simple identifiers that insert into the dirt after uncovering the tray. 

But plastic labels with clips can last from germination inside to the outdoor gardens. If the domes have covers, you can put the labels outside the crown until it comes off.

Finding the Best Type of Seeds

You can’t do anything we’ve discussed if you don’t have the most crucial ingredient – seeds. 

There are different types of seeds that you can start indoors, including flowers, vegetables, and herbs. It’s important to take note of the necessary sowing times of the different plant species.

Some seeds may require extra steps before sowing indoors. And then there are seed types that you can’t germinate indoors. Avoid planting arugula, lettuce, carrots, spinach, radishes, and beets indoors. These plants do best when put directly into the ground. 

Plants You Can Sow in january, february, march, and april

By May, most places are warm enough for summer seeds to go directly into the ground rather than germinating inside.

How to Start Seeds Indoors: What Are the 4 Steps?

If you follow these four easy steps, anyone can get seeds to germinate indoors. However, your success starts with having the right sources and getting your timing right.

Step 1 – Gathering Your Supplies

Start your task of germinating seeds indoors by getting all of your supplies together. If you make any of your materials, do it before you’re ready to plant your seeds.

Things you might make include your seed starter pots, plant markers, planting medium (soil), the drainage tray and humidity dome made with plastic wrap, and lighting shelves to hold your grow lights.

You’ll also need to ensure your viable seeds are purchased or acquired through a reputable source. 

Use this checklist to ensure you’ve got everything on hand to grow seeds indoors. 

  • Seeds
  • Starter pots (store-bought or homemade)
  • Planting medium – potting soil or soilless
  • Seed tray with dome 
  • Spray bottle of water

If you’re using plastic cell trays or other pots for starting your seeds, make sure they are clean, sterile, and dry. 

Your seed or propagation tray should be spacious enough to hold your pots. And it should be able to collect and store the water that comes out of your starter pods. 

This excess water can continue to moisten the soil as the seeds germinate. And when the humidity dome – a clear plastic lid – is over the tray, the water becomes condensed.

Step 2 – Filling Your Pots

Once you’ve gathered all your stuff, step two is to prepare your materials for planting. In this step, you’ll fill your seed pods with your seed-starter mix. 

But before you do that, you have to prepare your growing medium. In a large container, pour in the soil or soilless mix you’ll be using.

Then add in a healthy quantity of water. Finally, work the water into the dirt, adding liquid until you have the soil at the consistency of a damp sponge. 

It can take a few minutes before you get the right consistency when your mix contains peat. The way that peat can absorb liquid without expanding – like sand – can make it slowly fill up. 

Once you’ve got the mix properly moistened, start filling your pots. Add soil to the rim and then pack it down firmly. Refill to the brim and dust away the leftovers. 

Step 3  – Checking Your Seed Packet and Sowing

After you’ve filled your pots with soil, you’re ready to plant your seeds. But first, check the back of your seed packets to get the ideal depth of the seeds. 

You can poke holes into the dirt to put your seeds inside. Or you can add the seeds directly onto the soil and push them down with your finger or a pencil eraser.

Each container can have two to four seeds, depending on the type of plant. Small seeds can rest on top of the dirt uncovered. 

But larger seeds need darkness to germinate, so they need a layer of mix over the top. A rule of thumb is the layer of cover should be equal to the height of the mix – typically ¼” to ½.”

After you’ve put the seeds into the dirt, use your spray bottle to mist the soil. Don’t saturate the earth, since you’ve already pre-moistened it. 

Step 4 – Labeling and Positioning

Once you’ve got your seeds into the pots, you’ll need to add your labels. If you want to save time, pre-write your tags before you plant your seeds.

Then mark your pots after you’ve finished planting each species before switching to a new type of seed. 

Paper labels aren’t recommended at this stage, as they can deteriorate from the humidity of the dome. You don’t have to use anything decorative. Simple plastic stakes work fine.

What you include on your labels is up to you. At a minimum, you want to add the seed’s name. But you can also add the date that you planted the seeds. 

And if there’s room, you can add the length of the gestation period or the expected bloom date. 

After you’ve labeled your seeds, you can add the humidity dome. Then your trays are ready to put under grow lights.

In addition to growing lights above the trays, you can add the heat mat under the tray. 

What Are the Top Tips?

Once you’ve buried your seeds, your work doesn’t stop. The seeds will still need your TLC – tender loving care. 

Light Requirements

While your seeds grow inside their covered dome, you will want to keep the temperature around 65 to 75 degrees Fahrenheit. 

Full spectrum growth lights positioned 4″ to 6″ above the soil should provide enough light for seed germination. 

Your seeds can tolerate up to 16 hours of artificial sunlight daily. But, of course, the more time they have under the lights, the faster they grow. 

However, remember that your seeds will still need some darkness. So, don’t leave your lights on all the time.

Once your seeds germinate and seedlings emerge, you’ll need to increase the sun or light they experience. 

After taking off the dome, you can put the seedlings in a sunny (south-side is best) window. 

Watering Requirements

You introduce water to your seeds on several occasions. First, you moisten the soil mix before you add the seeds. 

Then, once you push the seeds into the holes, you mist the soil with a spray bottle for an extra spritz of liquid on top

Once you’ve put your seedlings into the seed tray and covered it with the clear dome, the mix of an enclosed space, heat from the light, and the evaporation of the water creates humidity.

This humidity can reduce the need to water your seeds after the initial dose. You want low humidity rather than high humidity. 

Keep an eye on the soil, doing your best not to lift the dome unless watering is necessary. Only water when the dirt is dry to the touch.

Seedlings will need constantly moist soil. Depending on the lighting exposure, you may need to water your new growths every other day or once daily. 

Avoid deep soaking the seedlings due to their shallow roots and the small container. Also, avoid watering directly over the seedlings. The force can cause damage to the delicate growths.

Thinning Seedlings

You usually use more than one for each pot when you plant your seeds. What happens is that you end up with several small plants growing together in the same container.

In most cases, you won’t use all of the plants you made viable. So, examine each new growth and select the sprouts that look the strongest and healthiest.

If you’re not keeping all the seedlings, you can snip or pinch off the shoots you don’t want to keep. But if you use them all, you’ll have to separate the roots delicately.  

Your seeds are ready for thinning and transplanting once they’ve developed two sets of leaves – the seedling leaves and their first pair of true (adult) leaves. 

Transplanting Seedlings

Your seedlings are ready to be transplanted once they’ve developed their “true” leaves. Some people like to transplant each viable seedling. 

But most people only transplant the healthiest growths from each batch. Your decision will depend on how many of each plant you want to grow. More plants equal extra work.

If you’re transplanting your seedlings outside, you might be able to leave your plant in its pot and put it directly into the ground. 

Otherwise, you’ll have to remove your new growths, clean the roots gently, and repot the delicate growths in a fresh potting mix. 

For container growing, choose a larger pot so the seedlings can grow. And fill the pot with the appropriate growing medium for the plant species.

When handling your seedlings, only touch the cotyledons – the first leaves. But avoid being rough with the tender roots.

After transplanting, your seedlings will require 12 to 16 hours of sunlight to make them grow strong and full, rather than leggy. 

Hardening Off

Before your seedlings are ready to transplant outdoors, you must harden them off. It’s an easy process that can take a week or two. 

To harden off seedlings, you need to get them used to being outside gradually. Start by putting the plants outside in a shaded, sheltered area.

Leave them out for a few hours and then bring them back inside before night. Continue doing this process for several days, extending the amount of time they stay outside each day.

After you’ve adjusted the plants to staying outside all day, you can acclimate them to the sun. You use the same process, starting with a few hours of exposure. And bring them in at night.

Stretch how long they stay out until the plants are outside all day in full sun. Once your plants can stay outside in the sun all day, you can also leave them outside at night. 

You can also transplant your seedlings into the garden at this point if you’re planting outside. 

Fertilizing Seedlings

Once you’ve thinned and transplanted your tiny seedlings, it’s safe to dose the plants with a dose of all-purpose fertilizer or a compost tea. 

Be sure that you dilute your feed mix and only use organic. Then, you don’t have to spend much time stressing over the nutrient content or understanding the chemicals. 

The Bottom Line – How to Grow Seeds Indoors

Growing seeds indoors can break the winter blues by giving you fresh, bright life. And it can provide you a head-start on having a gorgeous, award-winning garden. 

Whatever your reason for wanting to know how to germinate seeds indoors, you’re now equipped with all the knowledge to become a rocking indoor botanist.

Had an Enjoyable and Informative Reading Experience?

Growing your own houseplants from seeds is one heck of an accomplishment! Think you can care for a houseplant that comes from the nursery? Check out one of our articles below or take a look at all of our houseplant tip guides to see if you can master the needed skills. Ready to begin your growing journey right away? Make sure you have all the necessary gear to get the job done the right way.

Comment below or let us know your thoughts and feedback here. We love to talk plants! 

Photo of author
Sara Trimble
Sara Trimble was the lady who could kill a cactus. Today, she’s the fun and fabulous expert plant mom who rocks at growing the coolest, trickiest plants. Her favorites to grow are orchids, roses, succulents, and luscious vines. Sara has grown – and killed – hundreds of plants and she shares her green-thumb successes and failures to help other plant murderers discover correct plant care. In her spare time, she raises four kids, two dogs, and a husband.

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