When to Start Seeds
Inside or Outside, and a Seed Starting Planner
Starting your own seeds can be one of the most rewarding aspects of gardening, and growing from seed can be much cheaper than buying plants at the garden center. By growing plants from seed, you gain control over the variety, quality, and timing of your garden. However, determining the best time to start seeds indoors or outdoors and properly following the instructions on seed packets can be tricky, especially for beginners. In this guide, I will walk you through how to determine when to start seeds, whether they should be started inside or outside, and how to interpret and follow the important information on seed packets for a successful gardening season. Plus, I have an easy seed-starting spreadsheet which you can use to get yourself started!
Why Timing Matters for Starting Seeds
Whether you’re planting vegetables, flowers, or herbs, timing is everything when it comes to starting seeds. If you start too early or too late, you could face a range of problems, from stunted growth to missed harvests. Understanding your local growing season and following seed packet instructions is key to getting the timing right.
Some plants do well in pots for a long period of time and can just be potted up repeatedly. Some need more light. Others germinate well in the lower light levels of early spring. Some can't germinate until soil temperatures are warmer. Others prefer the cool wet of early spring and don't mind frost. Timing your seeds is all about making sure your seeds germinate and get a good start at life in optimal conditions – so they, and you, are successful!
Understanding Your Last Frost Date
To determine when to start your seeds, you'll first need to know the average last frost date for your region. This date marks the end of the cold season and the beginning of spring. Your last frost date will guide you in deciding when it’s safe to plant certain crops outdoors and when to start seeds indoors.
Find Your Last Frost Date: You can easily find the average last frost date for your area through local gardening resources, extension offices, or online frost date calculators.
Use the Last Frost Date for Planning: Once you know your last frost date, count backward to determine when to start your seeds indoors. This ensures that your plants will be ready to go outdoors as soon as the weather permits.
When to Start Your Seeds
If you are starting a lot of seeds, tracking when to start them can be tricky! So I have three suggestions – all of which are methods I use for my own garden.
Use a Seed Planning Spreadsheet
You don't even have to make one! I have one for you which you can duplicate and use for free! Here's how you use it:
Make a copy of it to your files. You will be prompted to do this right away.
Change the Last Frost Date to YOUR last frost date. Find that here.
DO NOT delete the information in the Sowing Date columns. Those dates will change as you input other information.
The spreadsheet is pre-populated with some simple-to-grow flowers from a GrowAlong that I did to show you what it looks like when everything is fully filled out.
Use your seed packets, and fill in the information for each variety you will grow.
Key information:
Common Name
Weeks from last frost. Use negative numbers for BEFORE last frost to get the right results.
Inside or outside
The dates will change for you. You can sort by inside and outside and/or by sowing dates.
Once I have filled out the spreadsheet, I transfer that information to two places:
Write the dates in your Gardening Journal
In my Garden Notes, I write what I need to sow on each weekly page. That helps me keep track of what I need to sow when. I also make notes about inside or outside and any special instructions I need to follow.
Write the Dates on the Seed Packets
Finally, I write the sowing date on the upper right hand corner of the seed packet. Then I organize my seed packets by the date that each should be sown. And I take them out to the Greenhouse!
Indoor vs. Outdoor Seed Starting: When to Choose Each
When deciding whether to start seeds indoors or outdoors, consider the plant’s specific needs and your local climate.
Indoor Seed Starting
Best for: Plants that need a longer growing season or are sensitive to cold. Also good for those of us in colder climates with erratic spring weather.
Indoor seed starting is ideal for plants that need to be given a head start before being moved outdoors. Many vegetables, flowers, and herbs need warmth and a stable environment to germinate and grow strong before they can survive outdoors.
When to Start Indoors: Follow the seed packet’s guidelines for the number of weeks before the last frost date to start seeds indoors. Generally, warm-season crops like tomatoes, peppers, and basil need to be started indoors 6-8 weeks before the last frost date. You’ll also need a grow light or sunny windowsill to ensure your seedlings get enough light to grow tall and healthy.
Indoor Seed Starting Tips:
Use seed starting trays or pots with drainage holes.
Use high-quality seed starting mix, which is lighter and more aerated than regular potting soil.
Keep the seeds in a warm location, ideally between 65-75°F (18-24°C), to encourage germination.
Outdoor Seed Starting
Best for: Cold-hardy plants or those that can be directly sown into the ground without needing a head start.
Outdoor seed starting works best for crops that are less sensitive to cold or have a short growing season. Some plants, like lettuce, peas, carrots, and beans, thrive when sown directly outdoors.
When to Start Outdoors: These crops can often be planted once the soil is workable and the last frost date has passed. For cold-tolerant plants, you may even be able to start them a little before the last frost date if the ground is warm enough.
Outdoor Seed Starting Tips:
Ensure the soil is loose and well-drained before sowing.
Plant seeds at the correct depth as indicated on the seed packet.
Keep an eye on local weather conditions to avoid planting when there’s a risk of late frosts.
Always keep frost cloth on hand to protect against those late-spring surprise frosts!
Using Season Extenders
Using season extenders can be a great way to start seeds outside but under shelter. This post has more information about season extenders and an easy DIY method to make your own.
How to Follow Seed Packet Instructions
Seed packets are your best guide to successfully growing your plants. They contain essential information such as planting depth, spacing, germination time, sunlight needs, and whether the seeds should be started indoors or outdoors. Here’s how to break down the critical elements on a seed packet:
1. Planting Depth
This tells you how deep to plant your seeds. Planting them too shallow or too deep can affect germination and growth. For example, small seeds may only need to be pressed lightly into the soil, while larger seeds may require a few inches of soil above them.
2. Spacing Between Seeds
This is important for preventing overcrowding. If seeds are planted too close together, they will compete for nutrients and space, leading to weak and spindly plants. Make sure to follow the recommended spacing guidelines for both indoor pots and outdoor garden beds.
3. Germination Time
Different seeds take different lengths of time to sprout. Keep track of how long it should take for your seeds to germinate, so you know when to expect results and how long to keep your indoor setup in place before moving plants outside.
4. Sunlight Requirements
Check if the plant needs full sun, partial sun, or shade. This will help you choose the correct location to start your seeds, whether indoors or outdoors.
5. Hardiness and Outdoor Planting Guidelines
Some packets will specify the ideal time to plant outdoors based on your region’s frost dates. If the packet advises waiting until after the last frost or once the soil temperature reaches a certain level, follow these guidelines to give your plants the best start.
Additional Tips for Successful Seed Starting
Keep a gardening journal: Track your planting dates, frost dates, and seed packet instructions to help improve your success in future seasons.
Acclimate your seedlings: Before transplanting seedlings outdoors, gradually introduce them to the outside environment. This process, known as hardening off, helps reduce transplant shock.
Consider seed starting kits: If you're new to gardening, seed starting kits that include trays, domes, and soil can make the process easier. My favorite seed starting equipment – including toilet paper rolls – is all listed here!
All of this makes it sound like starting seeds is hard. It's not! But paying attention to timing is important and will mean you have more success in the long run. Starting plants from seed is part-science and part-art. I am rather limited in seed starting space, so I have to be strategic about how many plants I start from seed, and which kinds. I largely focus on vegetables and flowers that I wouldn't be able to buy – sweet peas, specific annuals – but people with more space can start hundreds or even thousands of plants from seed every year! And I sometimes feel like I am not starting enough when I look around on social media.
Don't allow yourself to be overwhelmed or to compare your efforts to those of others! Remember: comparison is the thief of joy! If you start a tray of tomatoes from seed: Bravo! That is enough! I have to be careful. I am not a flower farmer. And this is not a competition! It's a garden!
No matter how many seeds you are starting, starting seeds indoors or outdoors at the right time is crucial to ensure your plants thrive. By following the guidelines on seed packets and considering your local climate, you'll be well on your way to having a successful gardening season. Don’t forget to plan ahead by finding your last frost date and understanding each plant’s specific needs. With careful planning and attention to detail, you’ll be able to grow a garden that flourishes all season long.
Happy Gardening!
