Growing Seedlings Indoors

How to Start Seeds Indoors

Image by Julio César García from Pixabay

In This Article

When to Start SeedsReading a Seed Packet
Gather Seed Starting SuppliesSteps for Indoor Seed Starting

Growing seedlings from seed gives you greater flexibility and control over your garden. You may cultivate your preferred types, the quantity of plants you require, and work within the planting dates that are appropriate for your growing location. If you buy all of your plants as potted nursery specimens, gardening may be an expensive hobby. Most vegetables and decorative plants, fortunately, can be grown from seeds, providing a considerably less expensive approach to populate your garden. Each plant has different requirements for sprouting seeds indoors. Seed depth, growth medium type, and water and light exposure requirements will all differ based on the species. However, the overall procedure for developing seedlings that may be transplanted into an outside garden is the same.

You may easily get from seed to seedling by following this straightforward, step-by-step guide. Just the information you require, nothing more.

When to Start Seeds

With directions like ‘start inside eight weeks before latest estimated frost date in your location,’ a seed package will often specify whether the plant should be started indoors. You may find out the anticipated last frost date in your location by conducting a quick internet search. The day on which you should start your seeds is determined by counting backward, for instance, eight weeks.

Reading a Seed Packet

You may find detailed information on how (and if) to start seeds indoors on the written instructions found on the back of seed packages. Among the most crucial pieces of information to search for are the following:

Packed for/Sell by Date

Similar to food goods, seeds are packaged fresh, therefore for the highest germination rates, choose this year’s harvest. To be sure they are still valid, look for a stamp that says the current year. Additionally, you could notice the expiration month. Depending on the plant species and storage circumstances, seed packets can live up to four years, according to the Oregon State University Extension Service. For best durability, keep them cold and dry. You can try old seeds if you come across them for sale or in your shed. However, purchase fresh for a full-priced investment.

Types of Seeds

There are many various kinds of seeds; let’s clarify some buzzwords like ‘organic’, ‘non-GMO’, ‘heirloom’, ‘hybrid’, and ‘open-pollinated.’

Organic seeds : are cultivated in accordance with USDA regulations. They are also non-GMO, according to USDA regulations. This indicates they were cultivated without the use of toxic chemicals, as well as other growth requirements.

Non-GMO Seeds: Seeds can be non-GMO without being organic. Despite not being genetically engineered, non-GMO seeds are not always cultivated organically.

Heirloom Seeds: A variety that has been handed down over several generations is called an heirloom seed. They are open-pollinated seeds. You can cultivate heirloom seeds in an organic or non-organic way.

Hybrid Seeds: To produce a new variety, two plants are deliberately crossed to produce hybrid seeds. They can be bred to be disease resistant, have a higher yield, and have other features. Despite not being genetically altered, hybrid seeds cannot be saved since they are not regarded as stable.

Open-Pollinated Seeds: This term refers to flowers that have been pollinated by wind, moths, or bees. Some seeds that are open-pollinated can also self-pollinate. Seeds with open pollination are not hybrids. Some people believe that open-pollinated seeds have better flavour than hybrid seeds.

Annuals vs Perennials

Your seed packet will likely indicate whether the flowers are annuals or perennials if you choose to plant flowers. Perennial plants will continue to grow for several years whereas annual plants only survive for one growing season.

Hardiness Zone

The zones that the plant is appropriate for may be listed on certain packets. If you’re unsure about your US growth zone, you may look it up on the USDA Plant Hardiness Zone Map. Plants and seeds suited for their geographic zones are typically available at garden centres. Always make careful to get items that are appropriate for your region whether shopping online or from a catalogue.

Light Requirements

Some seed packs will indicate whether the plant prefers full sun or some shade. Some will even specify the number of hours the plant needs to get each day. The majority of veggies require 6 to 8 hours per day.

Planting Depth

The majority of seed packs will specify the seed depth, or the depth at which the seed should be put before being covered with earth. The majority of seeds need to be gently driven into the ground between 2 inches and the surface (because they require light to sprout).

Days to Germination

If your packaging specifies “from 5 to 10 days,” this indicates you might see sprouts as soon as five days after planting. This implies that it might take closer to 10, or possibly a little longer, depending on the range mentioned above. This is an estimate, because the length of the germination period is affected by soil, light, moisture, and temperature conditions.

Quantity to Plant

Planting too many seeds is something new gardeners occasionally do. Unless you’re planting a cluster of seeds for something like chives or chamomile, you usually don’t need to put more than five seeds in the same place. The germination rate is the cause of this. How many of the seeds placed will really sprout? It would be terrible to sow one seed and then wait three weeks to learn that nothing occurred. Sometimes the seed packaging will provide a number to plant since some seeds don’t germinate.


Sometimes, seed packs will also indicate spacing. Typically, this is based on rows rather than square foot gardening. 


The size of the plant is occasionally mentioned on seed packs. The spacing should give you an idea, although an exact plant size is occasionally stated. The heights of flowers should be specified.


A plant is mature when it reaches its maximum height and has many leaves and stalks. It might flower, produce a crop, and complete its lifetime at this point. Planning events, such as when flowers could be ready for bouquets and crops might be ready for harvest, benefits from knowledge of the period from germination to maturity.

Direct Sow

Planting outside in the ground is known as direct sowing. It is typically advised to hold off until all frost threat has passed. That normally occurs in the Northeast in late April.

Start Indoors

You may sprout seedlings indoors before planting them outside. Packages specify when to do this, which should be after all threat of frost has gone.


This section outlines the window of time when you may anticipate seeing blooms on your plants, such as early spring or June through August. You might be able to construct a continually flowering garden to enjoy from spring through October by choosing plants with various bloom seasons.

Pre-Planting Prep

Some seeds need a little assistance to germinate because their coats are very tough. Before planting, lightly sand them if “scarification necessary” is written on them. Some may desire “stratification,” which is the stacking of soil in moisture. Others might need to soak. All are ways to crack them open just enough to let germination start. They might never grow if the necessary preparation is not done.


Herbs, vegetables, melons, and berries, for example, may offer instructions on how and when to harvest. Picking fruit at its optimum is critical for excellent health and the finest flavour and texture. Notes on harvesting procedure can be useful in avoiding potentially damaging a still-producing plant.

Level of Difficulty

The words “simple to grow” may appear on packaging. As previously stated, there is no assurance that your soil, light, moisture, and weather conditions will perfectly duplicate the optimal growing circumstances for a certain plant. Take this to heart if you come across types that are relatively challenging, and be prepared to plant extra just in case.

Extra Growing Tips

Extra growth suggestions, such as particular germination instructions, the frequency of watering necessary, or soil quality that can optimise your plant’s growing conditions, might be included in seed packs.

Gather Seed Starting Supplies

Plants require warmth, light, and water to flourish indoors, just like they do outside. Consider yourself lucky if you can locate a place indoors with access to water, temps over 70 degrees F, and 8+ hours of sunlight each day (mind you, this is in the winter). Most individuals don’t have all of those items, thus they must carry supplies to supplement all or part of these essentials. Before beginning your seeds, you need gather the following.

Equipment / ToolsMaterials
Grow light
Planting trays and small containers
Seed-starting mix or potting mix
Plastic bags or tray covers

Steps for Indoor Seed Starting

1. Get the growing medium ready

Before placing the potting mix into seed-starting trays or other individual containers, loosen and dampen it. This procedure aids in achieving a constant moisture level. Dampen the mixture until it resembles a wrung-out sponge. It should have no dry lumps and be moist but not pouring.

2.Fill the Containers

Fill your seed-starting trays or pots about two-thirds full with pre-dampened potting mix. To help the potting mix settle, tap the container on the countertop.

Firm the top of the mixture gently with your palm or a small board. Pack the potting mix into the container loosely; you want it to stay fluffy and aerated.

3. Sow the Seeds

Once your containers are ready, you may start planting the seeds. Check the seed box for any particular instructions. Some seeds may need to be pre-chilled or soaked. Some seeds require full darkness to germinate, while others require light. 

Planting depth is generally specified on the seed packaging. If no information is provided on the packet, the general guideline is to plant seeds two to three times as deep as they are broad. 

4. Finish Planting

Add extra wet potting soil over the seeds, then gently press down. For details on how much potting mix to layer on top of the seeds, check your seed packaging again. Generally speaking, the less you need to cover the seeds, the smaller they are. Some seeds, like lettuce, should be slightly covered with potting soil since they need light to grow.

5. Label the Seeds

You should name the seed containers while you are sowing so that you can track the progress of seedlings and determine when they are prepared for transplanting. Use popsicle sticks, plastic plant markers, and permanent ink pens to note the plant’s name and the date it was sowed for each variety of seed that was planted. The dirt along the container or tray’s border is where you should place the plant labels.

6. Keep Seeds Warm and Humid

Providing the ideal temperature, light, and humidity levels for seeds to germinate and sprout into seedlings is the most difficult aspect of beginning seeds indoors. Start by wrapping transparent plastic over the trays or containers. If you’re using recycled containers to start your seeds, this can be given by stiff plastic domes or coverings, like those that come with commercial seed-starting trays, or by transparent plastic bags or cling wrap. Heat and moisture are trapped by the plastic covering. (If your seed labels are too tall for the cover, cut them off and place them immediately above the corresponding cell on top of the cover.)

Place the container somewhere warm and draft-free so you can check on it every day. The ideal temperature for most seeds to germinate is between 65 and 70 degrees Fahrenheit, but check the seed packaging for details. The top of a refrigerator is a good place, or you may think about buying heating mats designed specifically for germination of the seeds. Under the potting pots, heating mats heat the soil from the bottom up. When utilising heated mats, you will often need to water more regularly.

7. Monitor Seedling Growth

As soon as you notice a seedling developing, take off the plastic and place the pots in indirect light. Generally speaking, seeds don’t require light until they sprout.

Your seedlings will begin to unroll and straighten as they start to poke through the dirt. There will be what looks like two leaves. To provide sustenance before genuine leaves are grown and the plant can perform photosynthesis, these leaf-like structures, known as cotyledons, are present in the seed. At this time, you should place your seedlings beneath a light source.

8. Add Light

For seedlings to develop into strong, healthy plants, they require a lot of light. It’s likely that your residence lacks sufficient natural light to support the growth of strong seedlings. In most cases, not even a south-facing window will do. However, you can generate the precise quantity of artificial light that seedlings need using grow lamps.

Avoid touching the seedlings while keeping the lights as near as you can (2 to 3 inches). Keep the lights on for 12 to 16 hours a day when seedlings first emerge. Use a timer to switch the lights on and off automatically to cut down on your hands-on time.

9. Keep Seedlings Moist

The sterile seed-starting media must be kept moist but not wet. To make sure the soil hasn’t dried up, check the moisture level at least once every day. A fungal disease called damping off, which swiftly kills seedlings, can develop as a result of unfavourable circumstances. By watering the pots from below and allowing excellent air circulation once the seedlings have sprouted, you can reduce the likelihood of damping-off disease.

Watering from the bottom allows the seedlings to absorb water through the drainage holes or porous walls of the container. Place the seed starting trays on a dish and, for 10 to 30 minutes, pour a thin layer of water to the bottom of the dish. Touch the top of the soil with your finger to confirm that moisture has reached the top of the container, then remove the seed trays from the water-filled dish and place them back under the light. You might also purchase a self-watering, seed-starting device.

10. Begin Feeding

The cotyledons will shrivel up as the seedling grows, and the first “real” leaves will appear. Your seedling starts aggressively photosynthesizing at this point. You will need to provide it with some more food at this point because it is growing in a soilless mixture. For strong roots and robust development, choose a balanced fertiliser or one high in nitrogen and potassium. Use a water-soluble fertiliser that has been diluted to half its normal strength since too much fertiliser would overwhelm the plants. Every two weeks, the seedlings should receive a modest feeding.

11. Pot Up If Necessary

Until you’re ready to plant seedlings in their permanent locations, they can stay in their original containers. However, once several sets of leaves have developed and the seedling is a couple of inches tall, it’s typical to transfer the seedlings into a larger pot. This process, known as “potting up,” gives the roots more area to expand. 3 to 4 inch pots are suitable for potting up to because they provide enough of area for root development. You can substitute potting soil for sterile seed-starting mix in the bigger container when you do this.

If more than one seedling is developing in a cell, just leave the stronger one. (This is “culling,” by the way.) Avoid attempting to remove the excess seedlings as this might harm the surviving seedling’s roots.

12. Harden Off the Seedlings

You ought to have young, robust plants that are stocky and healthy by the time the weather heats outdoors. You must harden off your seedlings in order to get them ready for planting outdoors once they are big enough. They become steadily more resistant to the elements, such as wind, rain, and sun.

Over a period of seven to fourteen days, move the plants to a shaded, protected outdoor location for progressively longer periods of time each day. As they become acclimated to the outdoors, gradually increase the amount of time spent outside and introduce direct sunshine. At the beginning of this phase, you will bring your seedlings inside or cover them at night if it appears that the temperature will drop. If the evening temperature doesn’t go below around 50 degrees Fahrenheit after the hardening off phase is done, you may keep them outside all night, unprotected.

Your seedlings are prepared for transplanting into the garden or into permanent outdoor pots once they can easily survive outside throughout the night. Before and after transplanting, give your seedlings plenty of water. The warmest and sunniest portion of the day should be avoided when transplanting.