I’m sharing some of the seed starting basics that have worked for me since building my greenhouse 3 years ago. I’m by no means an expert. But hopefully, I’ll be able to save you from making some of the mistakes I made along the way.
I am so ready for spring! I can’t wait to get my hands dirty and dig in the soil again! Starting your own seeds is not only a great way to get a jump on the season, but to grow many different varieties of flowers you may not find at a nursery. The amount of money it takes to buy a packet of seeds, will most likely cost the same as one plant!
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A Greenhouse is Not Your Only Option
I start the majority of my seeds inside the greenhouse. But there are other options if you don’t have one. Many gardeners grow plants in their basement, garage or kitchen. Just make sure you have the right seed starting supplies. I would recommend purchasing grow lights if you don’t have natural light. You can put a few trays on top of the fridge or radiator, to encourage seeds to sprout more quickly. Or if you have the room, I would suggest buying a heat mat. Starting seeds indoors will allow you to transplant much larger, more established plants into the garden, once the weather has warmed up.
Seed Starting Dates
To make certain not to start sowing seeds too early, be aware of the frost dates in your area. Read the recommended start times on the back of the seed packet or the catalog descriptions. There may be a few varieties that need to be started as early as 10-12 weeks before your last frost. Some of these are sweet peas and pansies. Most of the seeds I have purchased, will be started 4-6 weeks before my last frost date. If you sow the seeds too early, and the weather is still too cold to transplant, your seedlings may become too big for their pots. This could cause your plants to become root bound.
You can start seeds in just about anything that holds soil and drains water. Egg cartons or Dixie cups with holes put in them will work well. I use seed starting cell trays and bottom flats. If reusing old pots or trays, be sure to wash them thoroughly with a 10% bleach-90% water solution. This will help kill any lingering diseases or pathogens. Before you move to the next step, make sure you gather up the necessary supplies need for basic seed starting. You’ll need the folowing supplies:
- seed trays
- bottom trays
- seed starting potting soil
- clear dome lids
- shop lights
- heat mat
- plant labels
Tapping Down the Container Soil
Fill seed flats or containers to the top with a seed starting soil mix. Tap firmly against the table as you go, so the soil settles and there are no air pockets trapped in the tray cells. This will also make it easier to remove the seedlings once they are ready to be transplanted.
Watering the Right Way
Make sure you moisten the seed starting mix, prior to adding your seeds. It’s so important not to overhead water after you’ve placed the seeds in the container. You may wash the seeds away, and have to start the process over again.
Set the freshly sown seed flats in a waterproof tray with an inch of water in the bottom. This allows the seed to soak up the water from below, making it less likely to over water. Leave the water in the trays for 10-30 minutes, checking for moist soil every 10 minutes with your finger at the top of the container. Empty any remaining water once the soil surface is evenly moist. Check on your plant’s soil at least once a day. Seed trays should not be watered from overhead, until the plants have their first set of true leaves. Not only can the water from the hose wash tiny seeds away, but watering from the bottom allows the roots to be watered thoroughly.
Tools to Help Germinate Quickly
Seeds need to be kept warm and moist in order to germinate rapidly. Investing in a heat mat allows bottom heat to get your seeds started, and will help with the germination process. Unless the directions on the seed packet state otherwise, set the mat at 65-75 degrees. You can put a few trays on top of the refrigerator or a radiator as well. Using a plastic dome cover to keep up the humidity, will also help the seeds germinate quickly. Remove both the mat and plastic lid when the seeds start to germinate.
Use Only One Variety Per Cell Tray
An important seed starting basic is not to seed more than one type of flower in a cell tray. This is especially true if you plan to use a plastic dome lid. Unfortunately, I missed that recommendation the first year, and it was a definite issue. Germination rates vary by variety, so it is best to have all cells filled with the same seeds. If you are using grow lights, the varying heights between plants will also be a concern. The shorter plants within the tray can get leggy when the light is adjusted for the taller plants within the cell.
Seed starts need 12-16 hours of light to grow. If they do not have enough light, the starts will become leggy. I have not had an issue with there not being enough light in my greenhouse. But a grow light is a great idea. Especially if you are growing your seeds in a basement or somewhere where there is little light. If you are using a grow light, it is important to adjust it to be suspended no more than three inches above the top of your plants. Make sure you are adjusting the lights as the plants grow taller, so that they are 2-3 inches above the tallest plant.
Label Your Plants
Label each tray with the variety name and the date sown. It’s extremely important to label your seed trays immediately after sowing. I use Popsicle sticks and a sharpie. But I think I’m going to switch to a a waterproof label. This way, I can place it outdoors with the plant once I transplant it.
Other Seed Starting Basics
Make holes in each cell, using your finger, or a pencil. Most seed packets have directions as to how deep to plant the seeds. A general rule of thumb is to plant the seed twice as deep as it is big. Drop 1-2 seeds into each hole until the tray is completely full. Cover the tray with a light dusting of fine vermiculite, or seed starting mix, making sure all the seeds are covered.
Many hardy annuals do not like being transplanted, and actually do best when sown directly into the soil. Before direct sowing, make sure all danger of frost is gone.
If you have leftover seeds after sowing, you can use them for future use. Be sure to store your seeds in a cool, dark and dry place, free from rodents or insects. Most seeds will maintain their viability for up to two years, but the germination rates will decrease over time.
As the plants grow, they will need to be fed. Add the amount of liquid seaweed and fish emulsion, stated in the instructions, to your watering can and drench plants weekly.
Having a fan running in the greenhouse, can help with circulation. The gentle breeze stimulates young plants, which helps to prevent spindly, weak growth.
Don’t Forget to Harden Off Your Plants
You will need to prepare your seedlings for the transition outside. It is crucial to “harden off” your seed starts to prevent them from going into shock by the sudden change in temperature. For a couple of weeks, set the pots and trays outside in a sheltered area, increasing the amount of time they are out each day. This will help acclimate the seedlings to their new outdoor environment, and temperature fluctuations. Once all danger of frost has passed, they can be transplanted in the garden. If you suddenly take these starts from that warm space they’ve been used to, and expose them to bright sun, the wind and temperature swings in the open garden will be stressful to the plant.
I know all of this can seem intimidating for new gardeners, and it still makes me nervous at times. But don’t let that keep you from having fun, and making this a wonderful learning process! I hope by following these seed starting basics, you will feel like you at least have a place to start. Mistakes are inevitable, but learning and “growing” from your mistakes, is what makes this entire process worth it! Please let me know if you have any questions!
And here is my favorite gardening book of all time! Floret Farm’s Cut Flower Garden: Grow, Harvest & Arrange Stunning Seasonal Blooms, by Erin Benzakein with Julie Chai. Erin’s first book is the reason I built a greenhouse to grow my own flowers. My husband says it was the most expensive book he ever bought me! Her expertise and gorgeous flowers inspire me greatly! 95% of everything I’ve learned, has come from this resource. I use this book throughout the year, and I’ve learned so many seed starting basic tips from Erin. Oh, and have I told you that I buy my flower seeds from Floret Flowers? I’m such a fan!
I hope these seed starting basics helped you understand what steps need to be taken when deciding to grow your seeds indoors. If you have other questions that haven’t been addressed, please leave a comment below.