Seed Starting Guide (8 Key Steps to Start Your Garden The Right Way)


If starting a garden feels overwhelming, this guide is for you. We’ve broken down the entire process from ordering supplies to starting seeds and keeping them alive.

Read on to learn how to start your own garden in eight easy steps.

Step 1: Order Seeds & Supplies

Seeds

The first order of business, obviously, is to order seeds. There are no shortage of seed companies, but these are just a few of my favorites available online:

pumpkin seeds
You have lots of options when it comes to where you buy your seeds.

If you want to shop local, you can also find probably a good selection of seeds at your nearest grocery or garden/feed store.

Once you have your seed order in, that’s great! The hardest part of ordering seeds is narrowing down your selections to the few that you can reasonably manage. But seeds aren’t the only thing that you’re going to have to order. 

If you’re starting from scratch, you may need to order seed trays, lids, pots and bottom trays, and other garden tools and supplies. 

If you already have these materials on hand, take some time to inventory what you have. Then, clean your pots and tools thoroughly with a diluted bleach solution to start your seedlings off to a healthy start.

Repair or replace any broken tools, so you don’t have to worry about that in the middle of the growing season. 

Seed Trays

The most common number of cells in seed trays are 50, 72, 128, and 200 cells. The standard size is 1020 (you can learn more about 1020 seed trays here).

seed tray
Seed trays help you to start lots of seeds at the same time – and they make it easier to water them and move them as well.

50-cells are perfect for most vegetables. Flower seeds tend to be a little smaller on average and do well in 72s or 128s.

A standard-sized seed tray typically measures about 10 inches wide by 20 inches long. Some trays, called bottom trays, are open rather than divided into individual cells. Bottom trays may or may not have drainage holes, and both types have a purpose. 

Traditional seed trays are made out of plastic, but there are more options than ever on the market today. Peat pots are an excellent choice for environmentally-conscious gardeners.

These pots are biodegradable, and are a little easier on your seedlings too. Since the pots decompose in the soil, you can plant the seedling and pot directly in the soil and not have to worry so much about transplant shock. 

Possibly the best seed trays for healthy seedlings are winstrips, a type of seed tray available through Neversink Farm. These seed trays are more expensive but their unique design works to “air-prune” seedlings–meaning that seedlings roots’ stop growing when they come into contact with air, preventing the seedlings from becoming rootbound as they would in regular seed trays. 

Of course, the crafty gardener can forgo store-bought seed trays and make their own! For inspiration, check out this article

Humidity Domes

Humidity domes are plastic lids that fit over standard-sized seed trays. Humidity domes may be tall or short, and they may have vents or they may not. There are advantages and disadvantages of each. 

Humidity domes are perfect for germinating seed–the lids work to capture heat and moisture inside the flat, mimicking greenhouse conditions at the seed-starting level. For more information on humidity domes, read my article on humidity domes here

Heat Mats

Heat mats are another seed-starting tool that can exponentially improve seed germination. While not completely necessary for seed-starting, heat mats are recommended if your seed-starting room is in a cool place. 

Essentially a rubber mat that fits between one and four seed trays, heat mats work with a thermostat to raise the soil temperature to a preset level for optimal germination (more on optimal seed germination temperatures later).

Grow Lights

Possibly the most expensive investment you can make to your seed-starting room (other than buying a greenhouse), grow lights are a game-changer. According to BBC Science Focus Magazine, seeds don’t require light to germinate, seedlings do require light once they emerge from the soil. 

There are a variety of grow lights available, certainly, one to meet every budget. LED lights, favored by gardeners due to their high energy efficiency, come in white light or full-spectrum varieties.

White lights are fine for seed starting. However, as your seedlings grow, you’ll want to invest in a full-spectrum light that contains differing wavelengths that plants need for photosynthesis. 

Just remember to give your plants a little time away from the light (use a timer if necessary) – don’t leave your grow lights on all the time.

Potting Soil

Potting soil is another expense to consider when budgeting for your garden. To start seeds, you’ll want a seed-starting mix.

soil
Use a good seed-starting mix to help get your plants off to a healthy beginning.

If you’re sowing large quantities of seed, or if you just want more control over what’s going into your garden, you may be interested in making your own mix from scratch!

Check out my article on making your own potting soil mix here.  

Step 2: Do The Right Research

Know Your Hardiness Zone

If you already know what hardiness zone you are growing in, that’s great! If you’re not sure, go to this link and browse the USDA hardiness zone map.

frosted leaf
Unless you live in a very warm climate, you will have to plan your transplanting and seed sowing around frost dates.

Simply type in your zip code to find your hardiness zone. The legend on the right lists the lowest average temperatures and highest average temperatures for each zone. 

Read The Seed Packet

It goes without saying, but read the seed packet. You can find general instructions for planting any seed online, but these directions on the packaging were written with care from people who really know that particular variety. 

seed package
Seed packets tell you about time to germination (and other information) for a given plant variety.

You can also find information on disease resistance and other important information. To learn more about seed catalogs and what they tell you, check out this article.

Step 3: General Timeline For Starting Seeds

Cool-Season Crops

Cool-season crops like lettuce, brassicas, peas, and carrots can be started (and transplanted) outside a little earlier than other plants. Start these seeds indoors in early spring in temperate climates, or direct sow the seeds outside as soon as the soil can be worked.

pea plants
Peas are a cool-season crop, and can be started outdoors earlier in the growing season.

Warm-Season Crops

Warm-season crops like nightshades and squash won’t thrive unless they are planted after all danger of frost has passed. Some heat-loving plants require soil temperatures of at least 70 degrees or more, and many heat-loving annuals may take up to 100 days to mature and bear fruit. 

tomato plant 3-5-2021
Tomatoes are a warm-season crop, so you might need to wait a little longer to move them outside.

If you have long-season annuals like tomatoes or peppers, definitely start seeds indoors up to eight weeks before weather conditions allow those seedlings to be transplanted outside. 

Sample Planting Calendar

The Old Farmer’s Almanac has a free planting calendar available that is an excellent resource to use for starting seeds at the appropriate time!

calendar
Find your last spring frost date and work backwards to find out when to sow seeds indoors/outdoors or transplant.

Simply type your zip code into the search bar to create a table that lists first and last frost dates for your region, as well as a date range for when to plant common vegetables and herbs.

A general seed-starting timeline is represented below:

CropStart
Seeds
Indoors
TransplantStart
Seeds
Outdoors
Beetsn/an/a2-3 weeks
before last
frost
Broccoli7-8 weeks
before last
frost
1-3 weeks
before last
frost
2 weeks
before last
frost
Carrotsn/an/a2-3 weeks
before last
frost
Cucumbers3-4 weeks
before last
frost
2-3 weeks
after last
frost
n/a
Green
Beans
n/an/a1-4 weeks
after last
frost
Lettuce4-6 weeks
before last
frost
2 weeks
before last
frost to
two weeks
after
n/a
Peasn/an/a3-6 weeks
before last
frost
Peppers8-10 weeks
before last
frost
1-3 weeks
after last
frost
n/a
Radishesn/an/a6-8 weeks
before last
frost
Tomatoes6-8 weeks
before last
frost
2-4 weeks
after last
frost
n/a
This table summarizes the times to start seeds indoors, transplant,
or start seeds outdoors for some common garden vegetables.
You need to know the last frost date in your area!

The best way to decide on a date to start your seeds is to pick a date that you want to be able to transplant your seedlings outside.

Consider your growing region’s last spring frost and the specific needs of your plants, and count back the appropriate number of weeks to maturity listed on the packet for that particular variety.

Step 4: Sow Your Seeds

Seed-Starting Mix v. Potting Soil

When purchasing (or making your own) soil mixes, opt to start seeds in a seed-starting mix. Seed-starting mixes are lighter than potting soil mixes, and they don’t contain nearly as much organic matter or fertilizers as potting soil mixes. 

pottings soil mix plant in container
A seed-starting mix is lighter than a potting soil mix, containing less organic matter and fertilizer.

This is better, as small seedlings don’t need as many nutrients as older seedlings – and a mix higher in organic content will be more likely to spontaneously sprout green mold than a spongy seed-starting mix high in peat moss or coco coir. 

Here’s a sample recipe for starting seeds from Oregon State University:

  • 1 part compost
  • 1 part peat moss
  • 1 part perlite or sand

Moisten the peat moss prior to mixing, then add the compost and perlite. Combine all ingredients and mix thoroughly to ensure an even texture. 

Direct Sow v. Start Indoors

Some seeds are happily started outside, especially larger seeds like beans and squash – once the soil has warmed up enough for them.

These seedlings don’t love to be transplanted. If you do decide to start these seeds indoors, opt to use a biodegradable pot (like a jiffy pot or peat pot) so that you can transplant the seedlings without disturbing the root system. 

carrots
Carrots and other root crops do not transplant well, so sow them directly into the soil outside.

Some seeds – particularly flower seeds and sensitive vegetables like tomatoes, eggplant, and peppers – do better when started indoors. Especially if you live in a colder climate with a shorter growing season, you’ll want to start seeds indoors to get the maximum harvest out of your plants. 

Starting seeds indoors makes more work on the front end, but you’re able to completely control every aspect of your seedlings’ initial growth.

Open Flats v. Cells v. Pots

As previously mentioned, seed trays come in both open types and types with individual cells. 

Open trays are great for growing microgreens because you’ll want to sow the seedlings close together. Open trays are also perfect if you have seed that hasn’t been cleaned well–seed that you or a fellow gardener saved, that isn’t as clean as it would be, coming from a purchased seed packet. Multi-sow the seed and chaff (pieces of flower) into an open tray and bump up into bigger pots at a later date. 

aluminum trays
Open trays are a good choice for growing microgreens, since you don’t need individual cells for each seed.

Trays with cells are perfect for creating “plugs,” individual seedlings or seedlings in pairs that have separated root systems. When it comes time to transplant, simply pop the cells out one by one and plant them in the ground! 50-cell and 72-cell trays are just fine for most vegetables, and 128-cell and 200-cell trays are perfect for flower seeds, which tend to be smaller. 

seedlings in seed tray
Trays with cells help you to produce “plugs”, one for each seed, that you can transplant outdoors when the time is right.

You might choose to plant your seeds directly in pots if you anticipate growing a large plant or a plant that won’t be transplanted for a while. This article can help you to decide on clay or plastic pots.

repotting plants
Sow seeds directly into pots (as large as you need) to give them more time to grow before transplant.

Seed trays and flats are wonderful for conserving space, but if you have room (and the extra time needed to water pots), you might plant seeds in pots just to make the transition easier on your seedlings.

Tomatoes and peppers do well started in pots, as they have time to develop a healthy root system before they have to be transplanted to a bigger container 

Use These Tools

There are a few tools that actually make seeding enjoyable, rather than a chore! My favorite seeder, Johnny’s Hand Seed Sower, is one of the cheaper ones.

Simply pop the top, fill with the seed of your choice, put the lid back on, and spin the lid to select the correctly sized hole to send the seeds through. Put the seeder over your seed tray, tilt it slightly, and tap gently to release the seeds. 

The Earthway Precision Garden Seeder is my go-to for sowing seeds outside. This seeder is perfect for gardens with straight rows, but you can use this seeder in raised beds too.

The seeder comes with seven seed plates, although more sizes can be ordered. Extremely adjustable, you can set not only spacing between seeds, but the seed depth as well.

(You can learn some easy ways to sow small seeds here).

Cover (Or Don’t)

Whether you sow seeds indoors or outdoors, you’ll need to cover the seeds to protect them from the sun, wind, and animals. Some small seeds actually require light to germinate, and I’d recommend starting those seeds inside so you will have some control over their environment. 

seeds sprouting GU cover page
Seedlings need light after germination, and some small seeds need light to germinate.

A good rule of thumb to remember is to plant seeds twice as deep as they are big. Seeds planted too deep will never germinate, but seeds planted on the surface of the soil likely won’t make it either. 

Step 5: Water

Watering is an essential part of seed starting. I prefer to moisten my soil medium before I sow seeds, as an extra precaution.

You must be careful when watering seeds (especially small seeds) because overhead watering can move seeds around, or worse – the pressure could even wash them away. 

Bottom Water

You’ll want to keep your seed trays moist until the seedlings germinate, at which point you can allow the soil to dry out between waterings. Bottom watering is a safer alternative to overhead watering. 

seedlings in seed tray
Use trays to water seeds from below and avoid washing them away.

To bottom water, you’ll need a bottom tray without holes for each seed tray. Fill each bottom tray with a couple of inches of water, and sit each seed tray down in it. Wait for half an hour and then dump the excess water. 

Mist

You might choose to mist your seeds with a spray bottle or a watering wand turned to the gentlest setting. You’ll want to check on your seed trays every day, making sure that the soil isn’t drying out.

spray bottle head
Use a spray bottle to mist the soil and keep it just moist enough for your seeds.

Monitor temperature and humidity levels frequently to ensure that you don’t have green mold or some other unwelcome organism sprouting on your seed trays. 

If you aren’t already in the habit of watering your plants in the morning, make it part of your daily routine. The worst thing you can do for your seedlings is water in the middle of the day – you run the risk of burning delicate foliage in the harsh sun.

Avoid watering in the evening too, as the cold moisture promotes damping off and other diseases. 

Step 6: Soil Temperature

Heat mats work miracles in the seed-starting room. At the right temperature, some seeds will sprout in as little as three days!

tomtao seedlings
Your seeds will germinate much faster with the proper soil temperature – but it varies by plant!

The University of California has an excellent study on the ideal germination temperatures for some common vegetables, represented here:

CropMin
(°F)
Ideal
Range
(°F)
Max
(°F)
Beets40 65-8595
Broccoli4060-8595
Carrots40 65-85 95
Cucumbers6065-95105
Green
Beans
60 75-85 95
Lettuce3260-75 85
Peas40 65-75 85
Peppers60 65-75 95
Radishes40 65-85 95
Tomatoes50 65-8595
This table shows the minimum, ideal, and
maximum soil temperatures for seed
germination of various garden vegetables.

Step 7: Light

Natural Light v. LED Grow Lights

We tend to believe that natural light is always better for plants (and don’t get me wrong, it most certainly is), but one of the worst things you can do for your seedlings is to start  them in front of a window.

No matter where you live or which direction you’re facing, your seedlings won’t get enough natural light through that window and they’ll be forced to stretch for it, growing into leggy, spindly seedlings. 

daylight
Make sure your seedlings get plenty of light after they emerge, or else they will grow tall and thin as they stretch towards the light.

Instead, invest in a grow light if you’re starting your seeds in a room inside. There are so many options available, there’s bound to be something to fit your budget and your needs. 

LED lights are a little more energy-efficient than fluorescent bulbs, but they are a little more expensive. Regardless of which bulb you choose, be sure to invest in a full-spectrum light and not just white light–plants need the full spectrum to grow strong and healthy.

Light Requirements

According to the University of New Hampshire, seedlings can get by with eight to 14 hours of light per day.  To get plants to fruit, you will need to increase their “daylight hours,” depending on the crop that you have.

Shade tolerant plants like brassicas, spinach, and peas need between 10 and 12, and full sun plants like tomatoes, beans and squash need at least 14 hours per day, but not more than 20. 

Step 8: Continued Care

Fertilize & Feed

Once your seedlings have their first two sets of leaves, you might want to consider fertilizing them. One of the easiest ways to fertilize seedlings in a flat is to apply fish emulsion or compost tea. Fish emulsion can be bought at most garden supply stores. 

To make a simple compost tea at home, take kitchen scraps or aged compost from your garden and steep in a bucket full of water for at least 24 hours, up to two days. Pour the mixture through a small mesh screen, or cheesecloth or something similar, and apply the liquid fertilizer as you would normally water. 

compost bin
Use aged compost to make compost tea.

If you’re bumping up seedlings into bigger containers you can mix compost with potting soil or add a granular fertilizer to the mix. Seedlings need Nitrogen, Phosphorus, and Potassium, so look for a fertilizer labeled 1-2-1 or 2-2-3.

The numbers represent the percent of each mineral present (you can learn more about fertilizer numbers here). Dilute synthetic fertilizers, as the chemicals can actually burn your plants.

Thin Crowded Seedlings

If you multi-seeded a lot of seeds together, you will need to thin them before they become too crowded. If you’ve never thinned seedlings before, it feels awful.

tomato seedling
If you get a high germination rate for your seeds, you may end up with too many seedlings, which requires you to thin them. Sad, but true!

It’s not a hard task, but it’s not fun to kill so many seedlings that you worked hard to grow. But think about the bigger picture.

Your remaining seedlings won’t be healthy if they’re overcrowded. So do the difficult thing and help the healthy seedlings live! 

Pinch the weak seedlings off at their base instead of pulling them out by the root, so you don’t disturb the other seedlings’ root systems. Instead of tossing the discarded seedlings on the compost pile, try them on a sandwich or salad. 

You can learn more about how to thin seedlings here.

Harden Off Before Transplanting 

If you take nothing away from this guide, remember this. Do not skip this step! Seedlings that aren’t hardened off properly aren’t likely to survive the transition from indoors to outside. 

Hardening off is the process of gradually introducing seedlings to outside conditions. This includes temperature, moisture, wind, and light.

tomato plant 3-23-2021
Gradually expose plants to the outdoors instead of transplanting them all at once (to avoid a sudden shock).

To harden off seedlings, put the seed tray outside for a few hours a day for a week, and increase the number of hours spent outside the next week. Leave the seedlings outside for a few nights the following week, and then they should be ready for transplanting. 

You can learn more about hardening off seedlings here. 

Conclusion

While not comprehensive, this guide should serve as your primer to successfully start a variety of different seeds, indoors and out.  

I hope you found this article helpful. If so, please share it with someone who can use the information. 

If you want to read some of my most popular posts, please check out the “Best of GreenUpSide” page here. Enjoy! 

~Jonathon

About the author:
When not writing content or growing flowers in her native Virginia, you can find Sarah hiking a long-distance trail deep in the woods. Follow along with Sarah’s adventures at http://sarahcolliecreative.com.

Sarah C.

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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