Seed starting is one of my favorite parts of growing a vegetable garden. Long before you can get outside in the actual garden, starting vegetable seeds indoors gives you a jump start on the growing season and provides an early season chance to get your hands dirty. In this guide you can find detailed information on exactly how to start vegetable seeds indoors including when to plant, what seeds are best started indoors, what supplies you need for seed starting indoors, and the exact process for raising healthy seeds.
If you are experienced at starting seeds indoors you can also scroll through the article and read some of the common seed starting mistakes and how to trouble shoot near the bottom of this article.
Why Start Vegetable Seeds indoors?
There are a few reasons why you should consider starting seeds vegetable seeds indoors:
- Starting seeds indoors extends your growing season and allow you to raise crops that would not produce if you planted them outdoors.
- Depending on your garden conditions, starting seeds indoors can give your plants a healthy start that can often overcome issues with bugs and disease.
- You often get a higher rate of germination when you can control the temperature and the moisture of your seeds
- It’s fun! Growing seeds indoors lets you garden in the late winter and early spring.
What Seeds are Best to Start Indoors?
Not all seeds are good candidate to start indoors. Some seedlings don’t like to have their roots disturbed and some plants are fast growing and don’t benefit from an earlier start. Below are some general guidelines for which seeds are best to start indoors:
Good Seeds to Start Indoors
- Brussels sprouts
Seeds you can to Start Indoors but need Care for Transplanting
Seeds that Should Be Direct Planted in the Garden
This also includes other root vegetables like garlic and potatoes
When to Start Seeds Indoors
Once you’ve decided which seeds to start indoors, it’s time to come up with a plan for when to plant the seeds. Start by reading your seeds packets. You can use the guide in the image above as a rough estimate for when to start your seeds, but your seed packets will give you the best information for starting your seeds on time.
You will also need to determine your last frost date in your area. You can search for the average last frost date and the ‘frost free’ date. Average last frost means that half of the year the frost date is before this and half the time the last frost date is after this. The frost free date means that there is still a chance that there will be a frost after this date.
You can find your last frost date using the Almanac website.
How to Read a Seed Packet
Seed packs may be small, but they are packed with information. Each packet is a bit different, but you can generally find planting instructions, growing instructions, growing conditions (like sunlight) and more. Take note of the information on the seed packet and use this to plan your seed starting schedule.
You can see more details about reading seed packets here.
Seed Starting Equipment and Supplies
The next step if to gather all the equipment you need for seed starting. While you can start seeds with equipment you have and put your seed tray in a window, your seedlings will likely be weak and leggy. Try to build up your seed starting supplies overtime and you will increase your harvest and chance of success. Below are the items you should gather or purchase for seed starting. It’s also possible to purchase a seed starting kit.
- Seed Tray (and dome)
- Seed Starting Mix
- Grow Lights
- Heat Mat (optional)
- Spray bottle/watering can
- Plant labels
Complete Instructions for Starting Vegetable Seeds Indoors
Below you can see the simple and exact instructions for starting vegetable seeds indoors. If you are looking for another method for seed starting check out how to germinate seeds in paper towels.
Step 1 Create Your Seed Starting Calendar
As described above, you will need to determine when to start your seeds indoors based on the growing time, germination time, and the average last frost in your area. I group my seeds into 3 different groups based on the grow times and plant 3 times during the spring/winter.
Step 2 Gather Your Supplies and Set up You Seed Starting Area
Collect your supplies and set up your grow station. Most seeds do not need light to germinate, so you can place your seed starting trays on shelves with your grow lights, or place them in a warm place while the seeds germinate. Seeds germinate better with warm temperatures.
To set up your grow lights, you may need to use additional shelving. You want to set up the lights so that are just a few inches above the top of the grow trays. As your seedlings grow you will need a way to raise your grow lights.
Before using your seed starting mix, you will need to make sure the mix is wet and you can pack it gently into the seed starting trays. Once your equipment is ready it’s time to plant your seeds!
Step 3 Plant Your Seeds
To plant your seeds, place 2-3 seeds in each cell and press them gently into the moistened mix. Cover the seeds lightly with a mix. A general rule is that the bigger the seed, the deeper it needs to be planted. Since not every seed will germinate, planting a few seeds in each cell gives you better odds of having at least 1 seedling grow in each cell.
Step 4 Place in a Warm Place to Germinate
Once your seeds are planted, cover with a dome to keep the seeds moist, and place the tray in a warm place. If you have a heat map, place your tray on top of the mat. We have one room in our house with radiant floor heating and we place our tray directly on the floor in this room. You can also place your seed trays near a radiator.
Keep an eye of your seed trays and water gently if the mix begins to dry out. Several seeds need light to germinate, specifically lettuce.
Step 5 Remove Dome and Place Under Lights
After just a few days to a few weeks, you will start to see the seedlings start to sprout and emerge from the soil. At this point remove the dome from the trays and place the trays directly under the lights. You will want to provide your seedlings with about 15 hours of light each day.
Step 6 Adjust Lights, Water, Thin and Transplant as Needed
Continue to monitor the seedlings. You will want to ensure that they get enough light, water and space to grow.
Keep the light just a few inches above the seedlings. This can get tricky if the seedlings grow at different rates, but try to adjust as best you can.
Keep your seedlings moist without knocking them over. To do this, you can use a gentle watering can, or you can water from the bottom by adding water to the seed tray and letting the soil mix wick the moisture up to the plants. If you find evidence of mildew or mold, you can cut back on the water. Too much sitting water in the bottom of the tray will kill the roots.
Your seedling also needs space to grow. If you have multiple seedlings growing in the same cell, you will want to thin your seedlings. This is best done with a pair of scissors. Pulling the seedling up can damage the roots so simply cut off the stem at the base.
When your seedlings start to look strong and are 2-3 inches high you may want to transplant them into large containers. If the cells of your seed starting tray are already large, you can skip this step. Gently transplant your seedlings into a larger seed tray or individual pots.
Step 7 Harden Off Your Seedlings
When you approach your last freeze date and your seedlings are a few inches tall, it’s time to harden off your seedlings. Do not skip hardening off your seedlings! Hardening off your seedlings gives your new plants a chance to get used to the outdoor conditions.
Find a protected area outside (from both the sun and the wind) and place your seedlings outside. Start with just an hour during the day and slowly increase the amount of outdoor time for about 1 week. You seedling will become stronger and will be more likely to survive getting transplanted into the garden.
Step 8 Plant Your Seeds Outdoors
The final step of starting vegetable seeds indoors is planting them into the garden. If possible, you will want to choose an overcast day without a lot of wind to transplant your seedlings. Prepare your garden by removing any weeds and making sure the soil is amended. Dig a hole for each seedlings that is roughly the same size as the seedling. Turn the seedling upside down to get the plant out. If you have to handle the plant, avoid the stem and try to lift the seedling with the leaves.
Place the seedling into the hole and barely cover with soil. Gently tap the soil around the plant base and water to moisten the area around the seedlings. If it is very dry you will want to water the area around as well so that the moisture isn’t wicked away from the new roots.
Keep an eye on your new seedlings, if there is a cold snap, you can cover your seedlings to protect them from the cold. Especially for the first few weeks, keep the soil moist around your seedling and add mulch if needed.
Common Indoor Seed Starting Mistakes
Below are a list of the most common seed starting mistakes:
- Starting seeds at the wrong time: Read the seed packet and know your last frost date
- Using the wrong soil: Use the best seed starting mix to guarantee success
- Not providing warmth: Don’t let your seedlings dry out
- Insufficient light: Keep lights a few inches above your seedlings for 15 hours/day or more
- Not thinning or potting up: When seedlings get big, transplant into larger pots.
- Skipping the hardening off process: Don’t do it! Give your seedlings a full week to adjust to the outside world.
Questions About Starting Vegetable Seeds Indoors
What month do you start seeds indoors?
When you start your seeds depends on where you live and which seeds you are growing. Most spring seeds are started between February and April.
Do seeds need sun to start?
Most seeds do not need light to grow and will germinate in the dark with light. There are a few seeds (like lettuce) that do need light to germinate.
Which seeds should be soaked before planting?
Some seeds germinate better when they’ve been soaked prior to planting. In general larger seeds with a tough outer coating benefit from soaking. The best seeds to soak include: Examples of seeds that benefit from soaking include peas, beets, cucumber, corn, squash, pumpkin and beans. Many of these seeds are not the best choices for starting vegetable seeds indoors.
What’s your experience starting vegetable seeds indoors? Drop a comment below.