Seed Starting 101 - Growing a Cut Flower Garden Series

Are you thinking about starting a cut flower garden this year? There are so many benefits to growing your flowers from seed. I’ll share some seed starting tips I’ve learned along the way.

See all the blog posts in the GROWING A CUT FLOWER GARDEN series HERE.

Updated 12/29/2021

It’s always the same. Every January.

I daydream about my beautiful cottage-style garden. I long for the day that I can get my hands dirty and dig in the soil again. And I’ll be one step closer when I get my flower seeds in the mail.

You can see which varieties I plan to grow for 2022 HERE. You can also read my blog post HERE to see what I grew or planned to grow in 2021.

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Starting your own seeds is not only a great way to get a jump on the season, but a chance to grow different varieties of flowers you may not find at your local nursery. The amount of money it takes to buy a packet of seeds will most likely cost the same as buying one plant!

You Don’t Have to Have a Greenhouse to Start Seeds

Although I start the majority of my seeds inside the greenhouse, there are other options if you don’t have one. Many gardeners grow plants in their basement, garage, or kitchen. I would highly 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. 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.

My friend Stacy of Bricks ‘n Blooms, who is a Master Gardener, has just written a blog post on How to Start Seeds Indoors Without a Greenhouse. Make sure you visit her blog for some great ideas.

Know Your Last Frost Dates

One of the most important tasks when it comes to getting ready to sow seeds is to be aware of your expected last frost date in your area. My expected last frost date is April 18th.

Read the recommended seed sowing times on the back of the seed packet, or the catalog descriptions to know when the best time is to sow your seeds.

Varieties such as sweet peas and pansies need to be started as early as 10-12 weeks before your last frost date. Most of my seeds will be started 4-6 weeks before my last frost date, but I will be sowing seeds anywhere from 4 weeks to 12 weeks before.

Note: If you sow the seeds too early, and the weather is still too cold to transplant, your seedlings may become too big for their containers, causing your plants to become root-bound.

Supplies You Will Need to Sow Seeds

Here is a basic list of some of the supplies you’ll need to start your seeds for the season. I’ve also written a blog post Supplies Needed for Seed Starting for a more detailed look.

More About Containers

You can start seeds in just about anything that holds soil and drains water. If you are just starting out and want to save some money on supplies, you can create holes in the bottom of egg containers, plastic cups, or Dixie cups and use them as containers.

If you are reusing old containers or trays, be sure to wash them thoroughly with a 1 part bleach/ 9 parts water solution to help kill any lingering diseases or pathogens.

Watering the Correct 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.

Sowing Your Seeds

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.

Watering Your Seed Starts

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 overwater. 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° F. 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.

Note: If you are new to growing flowers from seed, and are in the process of researching which items need to be purchased, this might help. I learned that you may not have to buy as many heat mats and plastic dome covers as you might think.

Once your seeds germinate, you do not need to use these two items any longer. And because your seeds will be sown at different times depending on the variety (some at 8 weeks before the last frost date, some at 6 weeks), you can move the mat and cover to the next set of seeds you’re ready to start.

*Remove the seedlings from the heat mat and take the dome off once they have germinated.

Use Only One Variety Per Cell Tray

THIS ONE I LEARNED THE HARD WAY! Do not seed more than one type of flower in a cell tray. This is especially true if you plan to use a plastic dome lid. 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.

Providing Light

From every blog post I have read, seed starts need 12-16 hours of light to grow. If they do not have enough light, the starts will become leggy. I personally have not had an issue with there not being enough light in my greenhouse, even with only 9-12 hours of light when I start the seeds in February and March.

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 3-in. 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. You can also use craft sticks and a sharpie. However, make sure to use a waterproof label when you transplant the seed starts outdoors.

Direct Sow Hardy Annuals

Many hardy annuals do not like being transplanted, and actually do best when sown directly into the soil. The seed packet will usually have information on the back of the seed packet, instructing you to directly plant outdoors. Before direct sowing, make sure all danger of frost is gone, unless directions state otherwise.

For certain varieties of flower seeds, you’ll have the choice to either direct seed or start indoors. If you choose to start indoors, you can speed up germination for these cold-tolerant varieties, such as Larkspur, by chilling seeds in a refrigerator or freezer for a week before sowing.

Using Leftover Seeds

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.

Feeding Your Seed Starts

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.

Run a Fan for Circulation

Having a fan running in the greenhouse will help with circulation. The gentle breeze stimulates young plants, which helps to prevent spindly, weak growth.

Providing proper ventilation in your greenhouse with exhaust fans helps protect your vulnerable new seedlings from diseases and pests. Aside from keeping optimal temperatures, exhaust fans also help with humidity management.

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.

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.

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.

I know this process can be 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 fun learning process!

See all the blog posts in the GROWING A CUT FLOWER GARDEN series HERE.

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 in the comments below.

Until next time,

Happy Gardening!

Make sure you visit my friend Stacy of Bricks ‘n Blooms to find out how to grow seeds without a greenhouse.

Seed Starting 101 – Growing a Cut Flower Garden Series