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How to Grow Seeds Indoors

How to Grow Seeds Indoors

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Whether you live in a place without outdoor space (like us) or are just looking for an opportunity to jump-start your growing season, planting seeds inside may be a great option for you.

In this article, we’ll teach you how to get into the practice of seed starting in your very own home, creating a new plant. You’ll go from planting new seeds to having sprouts and your very own food or houseplants in no time. What’s more, when you sew a seed indoors, it can actually give you a head start on germination during the growing season. It’s really the best way to start your seeds.

We’ll go through the basics, show you how to successfully germinate your seeds, and explain the right growing medium, light, and water needed for the best chances for success.

Did You Know?

Did you know that, when growing outdoors, it’s important to consider the frost date. That said, the latest frost date does not necessarily mean you should sow all the seeds in your garden. It’s only a projected date that anticipates the end of evening temperatures below freezing.

Pros and Cons of Starting From Seeds

If you’re looking to get started with seed growing in your indoor garden, you should be fully aware of the benefits and drawbacks. We’ll run you through these now.

Pros

There are several upsides to starting from seeds.

  • Seeds are cheap: Seeds are the most inexpensive way to start a garden, so if you screw it up the first couple of times, you don’t have to be worried about losing the farm.
  • Seed starting can happen indoors: This is helpful because depending on where you live, the growing season could be limited – and in many cases, sporadic. You don’t want to put a particularly delicate plant outside if you live in Michigan where surprise snow in the first week of May might ruin things. 
  • There’s more variety: Your local nursery only has so many mature or young plants on hand. There are online options for seeds of all kinds, and you’re able to start and germinate whichever ones you want.
  • There’s a certain satisfaction to it: There’s an undeniable pride factor to the fact that you’ve taken this fragile life form from seed to garden or even to your table. It’s just cool.

Cons

As with anything else in life, there are also downsides to a decision to start from seeds.

  • Some seeds are more finicky than others: There are certain plants that are easier to start from a seed, while others can be temperamental. With that in mind, it’s important to do research on what you’re thinking about growing in advance so that you can be aware of what you’re getting into.
  • Timing is still important: You can start seeds indoors, which can help you save a plant from one or two early spring frosts, but you still need to get certain plants in the ground fairly early on so that the root systems develop properly. It’s important to know what USDA hardiness zone you fall into climate-wise. That way, you know what will thrive in your area and when to get it in the ground.
  • Some plants do best in specific germination environments: You will need to do specific research on the environment your plant needs to begin its growth cycle in the healthiest possible way. Some plants are going to require specific amounts of light or air circulation, so growing from seeds can require varying amounts of upfront investment and initial setup on your part.

For plants that are particularly hard to grow from seeds, getting plants or sprouts that began life in a highly-controlled nursery environment may be easier. If you go this route, just be sure it’s a plant that doesn’t mind being moved into more permanent soil later on.

Did You Know?

Did you know that a heating mat can be used to provide your seeds with a steady temperature, which can help support germination? You can purchase heat mats either online or at local garden centers.

Which Seeds Should Be Started Indoors?

The University of Clemson Cooperative Extension Home and Garden Information Center lists several plants that should (and shouldn’t) be started indoors. There are several different types of vegetables you can grow indoors including potatoes, carrots and eggplants. Here’s a look at a table that shows the dificulty level of growing specfic seed types inside.

Similarly, seeds for a variety of fruits, such as tomato plants can be easy to germinate inside and then transplant outside when they’re ready. Check out the transplanting difficulty level on these fruit seeds, including avocados and tomato seeds. 

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Vegetable Seeds and Fruit Seeds

Some warm weather plants like tomatoes are easily transplanted and it’s ideal to start them indoors, particularly in cooler climates. With other plants, it’s not as common to start the seed packets indoors, but you may find it easier to get these going with the appropriate planning and research into what you’re looking to grow.

Plants That Can Be Started Indoors by Difficulty Transplanting
EasyTransplant With CareStart Outdoors
EggplantsSquashCarrots
PeppersPumpkinsCorn
AvocadosMelonsBeans
Tomato PlantsCucumbersBeets

 

Flower Seeds

Like vegetables and fruits, you can start a flower with your very own seeds. Use this chart, provided by the University of Missouri Extension for a germination guide to sowing common annual flowers seeds in the home.

Flower typeGermination timeGrowing tempCrop timeComments
Ageratum5 to 8 days60 to 65 degrees F10 to 11 weeksNeeds light to germinate.
Alyssum, sweet4 to 8 days50 to 55 degrees F8 to 9 weeksNeeds light to germinate.
Aster8 to 10 days60 to 62 degrees F7 to 8 weeks 
Begonia, fibrous10 to 12 days60 degrees F16 weeksNeeds light to germinate.
Celosia6 to 10 days65 to 68 degrees F10 to 12 weeksDon’t grow cool.
Cleome10 to 12 days70 to 75 degrees F7 to 9 weeksTransplant before flowering.
Coleus8 to 10 days65 to 75 degrees F9 to 10Needs light to germinate.
Cosmos5 days65 degrees F4 to 6 weeks 
Dianthus5 to 7 days50 to 55 degrees F12 to 14 weeksCover seeds lightly. Grow cool.
Dusty Miller10 to 15 days60 to 65 degrees F11 to 12 weeksNeeds light to germinate.
Geranium, seed7 to 10 days60 to 65 degrees F13 to 15 weeksBest if grown in small pot.
Gomphrena10 to 14 days68 degrees F9 to 10 weeksCrop time for dwarf types.
Impatiens15 to 18 days58 to 60 degrees F10 to 11 weeksCover seeds lightly.
Lobelia15 to 20 days60 degrees F11 to 12 weeksNeeds light to germinate.
Marigold5 to 7 days65 to 68 degrees F8 to 12 weeksTall types require more time.
Melampodium7 to 10 days60 to 62 degrees F7 to 8 weeks 
Nicotiana10 to 15 days60 to 62 degrees F9 to 10 weeksNeeds light to germinate.
Nierembergia10 to 15 days60 to 62 degrees F10 to 11 weeksKeep cool during germination.
Pansy/Viola6 to 10 days50 to 55 degrees F14 to 15 weeksGrow at cool temperatures.
Pepper, ornamental8 to 10 days60 degrees F11 to 14 weeks 
Petunia6 to 12 days55 to 60 degrees F12 to 13 weeksNeeds light to germinate.
Phlox, annual6 to 10 days50 to 55 degrees F10 to 11 weeksDirect seed into containers.
Portulaca6 to 10 days65 degrees F12 to 13 weeksNeeds light to germinate.
Salvia12 to 15 days60 degrees F9 to 11 weeksNeeds light to germinate.
Snapdragon7 to 12 days45 to 50 degrees F15 to 16 weeksNeeds light. Grow cool.
Statice15 to 20 days50 to 55 degrees F8 to 10 weeksGrow at cool temperatures.
Stock10 to 14 days50 to 55 degrees F9 to 10 weeksGrow at cool temperatures.
Torenia10 to 15 days55 to 60 degrees F12 to 13 weeksNeeds light to germinate.
Verbena12 to 20 days55 to 60 degrees F12 to 13 weeksChill seeds before sowing.
Vinca10 to 15 days65 to 68 degrees F14 to 15 weeksGrow in warm temperatures.
Zinnia5 to 7 days60 degrees F8 to 9 weeksDirect seed into final container.

 

Where to Get Seeds?

If you want to start growing from seeds, there are various options which may be available to you. You could certainly start at your local nursery. The advantage here is that you’ll know for sure that they are stocking options suited to your particular climate. However, local nurseries are likely to be beholden to whatever sells best in order to make the most money possible given limited shelf space. With that in mind, you can turn to specialty online sellers if you want more options.

These are just a few of the options, but the real key here is that the best of the sites will let you select seeds and other materials suited to your particular climate zone, based on the USDA hardiness recommendations referenced earlier.

What Containers Are Needed for Starting Seeds Indoors?

You’ll need a place to start your seeds. While there are going to be some traditional options on this list, you can also use other materials you have around the house.

  • Seed trays: This is one of the most common methods of going about finding a starting container. The advantage of this is if you go to any nursery or site online, they’ll give you guidance about what size to get all based on what you’re trying to grow.
  • Plastic bags: One thing you can do if you don’t have a ton of time to water your plants is create a plastic bag growing environment which will help with water retention. When you do this, you want to water them for a few days outside the plastic bag. When you put the seeds in the bag environment, you want the soil to be moist but not too wet. Too much water isn’t good for the root system. When you put plants under plastic, you’ll want to keep them out of the window because the plastic works as an insulator and can superheat your plants. Of course, plants need light, so be sure to remove the bag every once in a while and give them the sun they need. Finally, poke holes in the bag for air circulation. Plastic wrap should work as well as a bag. If you have a bigger planter box, one of the options you have is to plant right within a bag of topsoil as long as you cut drainage holes in the bottom of the bag.
  • Peat pots: The advantage of peat pots made from peat moss is that they are biodegradable, so if you wanted, you could choose to put them right down the soil and never have to worry about transplanting certain plants depending on the size.
  • Egg cartons: Cardboard egg cartons can be cut apart and used to plant seedlings. You don’t have to worry about removing the cardboard either because it will break down as it sits in the soil.

Preparing the Potting Soil

You want to make sure you have the right soil (or lack thereof) to thrive in an indoor environment. It’s possible to use the soil from an outdoor garden to grow your seedlings, but there are some drawbacks to this. There are often things like fungi, weed seeds and other disease-causing spores and bacteria that you really don’t want in your house. A well-regulated seed-starting mix will also do a better job of providing drainage.

As far as feeding the plants, you’ll want to take a look at liquid fertilizer. It’s easy to apply and may be better for starter plants because it can be applied directly on the plant and more easily absorbed.

Soil Mix or Soilless Mix?

One of the best ways to plant seeds indoors is with a soilless mix. This is usually based off of peat moss which is light and also provides a sterile growth medium while retaining water well.

Additives like perlite and vermiculite can be included in your potting mix to help provide the right combination of airflow, drainage and water retention. It’s important to research the right mix of these ingredients for your appropriate environment based on what you plan to grow.

Seed Starting Trays

When it comes to your seed starting trays, make sure you have enough space for what you’re planning to grow. Some things will do just fine in the egg carton containers, but plants with bigger root systems will need more room for their root system. Be prepared to get larger containers.

You should also consider what plants will need to be transplanted in order to determine the right container, which typically needs to happen when they are at least three inches tall and have their second set of leaves present. If they will need to be moved to a more permanent environment when the seeds sprout, reusable starter containers that can be used for multiple plants in the course of their lifetime will be cheaper. If the plants won’t be moved, consider peat pots or another material that will degrade over time in the soil.

Drip Trays

Plants, particularly developing ones without extensive root systems, won’t retain all the water you give them. They’re going to weep. Because of this, you may want to purchase drip trays to contain the runoff so that your entire living space doesn’t become a soggy mess.

The size of your water mitigation system is going to depend on the size of the plant, so keep this in mind. You should be able to get these at any nursery or hardware store.

Starting Seeds Indoors

Now that you’ve got your basic materials and maybe even some seeds at this point, it’s time to think about when and how you start this enterprise.

As a general rule of thumb, it’s a good idea to start your seeds inside up to six weeks before they need to be moved outside, if they’re going to be moved at all. However, that’s going to depend on local climate conditions and the plant itself. All plants require different germination times.

How Many Seeds Should You Plant?

Typically, you only want to plant two to three seeds per hole. There is not a 100% germination rate for seeds, so they may not all sprout. Having extra seeds improves the changes that a plant will germinate and grow. 

How to Start Planting: Seeding

When you start planting, follow the directions on the back of the seed packet in order to make sure you’re planting the seeds at the proper seeding depth. If you don’ know what the seeding depth should be, a good rule of thumb is to plant the seds 4x as deep as the width of the seed. 

One thing of note is that tiny seeds should barely be covered with soil, while larger seeds need to be slightly deeper.

Beyond that, there are considerations for your plants in terms of how much light, water and heat they’re going to require and how you as a plant parent can deliver on those needs.

How Much Lighting Do Seeds Need?

Different seeds have different light needs as they first germinate. There are some that germinate better in the dark, others that germinate in bright light, and some that don’t seem to care either way. You’ll need to refer to your seed packet for the right info on your specific seeds. 

Read our blog: Difference between Grow Lights Vs. Regular Light

For the plants and seeds that need a lot of sunshine during the day, such as kale or green beans, you’ll want to place them in a sunny window, preferable in a south-facing window to get the most light opportunity. If you live in the city and have limited lighting available, you may need to shop lights for best results, such as fluorescent lights or other grow lights. This can be the best way to ensure that you have enough light for proper germination.

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Checkout this Fullspectrum Grow LED Light from Green Bean Buddy.

At What Temperature Do Seeds Germinate?

While lights and sunshine will likely produce some level of heat, it’s important not to exclusively rely on your light to produce the needed heat. 

Most seeds germinate in a soil temperature that is anywhere between 65-85 degrees. For most people growing indoors, this range falls within room temperature. However, if you’re planting seeds in a drafty basement during the winter (do basements get drafts?), the easiest way to check the temperature of the soil is with a soil thermometer. 

If it’s too cold, consider purchasing a heat mat to provide sufficient bottom heat. 

Here are the ideal ground temperatures for specific plants.

CropsMinimum Temp (F)Optimum Temp (F)Maximum Temp (F)
Asparagus5075-8595
Lima Beans6075-8585
Beets4065-8595
Broccoli4060-8595
Cabbage4060-8595
Carrots4065-8595
Cauliflower4065-8595
Swiss Chard4065-8595
Garlic3265-8595
Leeks3265-8595
Lettuce3260-7585
Muskmelons (Cantaloupe)6075-85105
Okra6085-95105
Onions3265-8595
Parsley4065-8590
Parsnips4065-8590
Peas4065-7585
Peppers6065-7595
Pumpkins6085-95105
Radishes4065-8595
Spinach3265-7575
Squash6085-95105
Tomatoes5065-8595
Turnips4060-95105
Watermelons6075-95105
Source: California Master Gardener Handbook, 2nd edition, Regent of the University of California, Division of Agriculture and Natural Resources, Publication 3382 (Table 5.2, page 114).

How Much Should I Water Seeds?

When you first plant seeds, water is what will start the germination process. That said, too much water will cause them to rot, while too little could cause the embryos inside to die. You should lightly water your seeds, and you’ll need to continue watering them at least daily to keep the soil moist. You can use a spray bottle to do this or a watering can, but be sure not to overwater your plants. Drainage is incredibly important, too, as you don’t want standing water. 

Seed Starter

Another option to improve and monitor your watering is to purchase a seed starting kit lid, which can hold in the humidity while also providing the air circulation needed. 

How often Should You Fertilize Seedlings?

As surprising as it might sound, young seedlings typically don’t need fertilizer at first. They have enough nutrients inside them to germinate, even if there aren’t enough nutrients in the soil. But once you notice sprouting and leaves start to appear, you should consider fertilizer. An all-purpose, water soluble fertilizer is a typically good option, such at this one from Gardeners.com or from any local garden center.

Thinning Seedlings

Once your seeds have germinated and started sprouting, you may need to thin your healthy seedlings. The main reason you would need to thin is due to planting multiple seeds (remember – two to three) to increase the odds of success. If multiple seeds have germinated in the same space, you’ll need to thin the seedlings.

In the end, you want to make sure that each plant has room for development – both above and below the soil. Having them too close together can cause your seedlings not to get enough sunlight or air-circulation. To thin your seedlings, remove the weak or unwanted, which can be removed with scissors at the soil level.

Can You Use Old Seeds?

Many gardeners get a little seed crazy when they start prepping their gardens and purchase more seeds than they need. But can those seeds be reused in future years? The  quality of the plant should change if the seeds germinate, but the likelihood that they germinate goes down the longer they go without being planted. According to Under the Solano Sun, seeds in good condition will last at least a year, and may even last longer. Here’s a table that gives you an idea of the shelf life of your seeds:

1 Year2 Years3 Years4 Years5 Years
OnionsCornCarrotsPeppersBeets
ParsnipsPeasLeeksChardTomatoes
ParsleyBeansAsparagusPumpkinsEggplant
SalsifyChivesTurnipsSquashCucumbers
SpinachOkraRutabagasWatermelonsMuskmelons
 Dandelion BasilCelery
   ArtichokesCeleriac
   CardoonsLettuce
    Endive
    Chicory

Troubleshooting: Why Didn’t Your Seeds Germinate?

Did your seeds not germinate when you planted them indoors? Here are the main reasons that you can use for some DIY troubleshooting:

  • You planted the seeds incorrectly – too deep or not deep enough
  • You over/underwatered your seeds
  • Your potting mix didn’t have proper drainage or you used a garden soil mix with pathogens that potentially caused damping off
  • You used seeds that had already expired
  • You provided your seeds with the wrong amount of light (too much or too little, depending on the seed)

In most cases, your seeds didn’t germinate due to user error, which is nothing to be ashamed about. Most seeds grow very quickly, so it’s not difficult or expensive to start again. Just keep trying and work out the kinks along the way.

Conclusion

Starting from seeds indoors can be a fun way to start your garden at any time of the year. And even though this article is long, it’s typically a pretty simple process. Take what you’ve learned and get started with your very own indoor garden today!

Let's grow together!

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Sunday 8th of May 2022

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