Seed Starting 101: Growing a Cut Flower Garden Series

Are you thinking about growing a cut flower garden by seed but aren’t sure where to start? I’ll share the benefits of growing flowers from seed and basic seed-starting tips I’ve learned along the way.

Starting a cut flower garden from seed 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.

Another great reason for growing flowers from seeds is how cost-effective it can be. The money it takes to buy a packet of seeds will most likely cost the same as buying one plant!

One of my favorite things about gardening is the entire process of starting my cut flower garden from seed in my greenhouse. There is such a sense of accomplishment when you see your first small seedlings sprouting from the soil!

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I’m a self-taught hobby gardener, not a Master Gardener. Everything I share with you on my blog is my personal opinion and things that have worked for me personally.

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

Although I start most of my seeds inside the greenhouse, there are other options if you don’t have one.

Many gardeners grow plants in their basements, garage, or kitchen. If you’re starting seeds in a space without a natural light source, I highly recommend purchasing grow lights for adequate light.

You can put a few trays on top of a radiator to encourage seeds to sprout more quickly. If you have the space, I would suggest buying a heat mat.

Starting seeds indoors will allow you to get a head start with the season and transplant much larger, more established plants into the garden once the weather has warmed up.

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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. You can check your frost dates on the Old Farmer’s Almanac website.

When starting the process of growing a cut flower garden by seed, 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 the seeds I’ve chosen to grow this year will need to be sown 4-6 weeks before my last frost date.

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.

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Supplies You Will Need to Sow Seeds for Your Cut Flower Garden

Here is a basic list of the seed-starting supplies you’ll need for the season. You can also read my blog post on Supplies Needed for Seed Starting for more detailed information.

• Quality seeds
• seed starting soil mix
• vermiculite
• 72-cell trays or other containers with drainage holes
• drainage tray 
• humidity dome
• heat mat – I use the ones with a thermostat
• grow lights
• plant tags or labels

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What You Need to Know About Containers

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

Peat pots are a good option as well.

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

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Use Moistened Seed Starting Potting Mix

I use a high-quality organic seed starting potting mix for sowing seeds.

A seed starting mix is better for sowing seeds than regular potting soil because it has a finer texture and higher porosity. This allows for better water and oxygen access for seed germination.

It also contains fewer nutrients, which is beneficial because it prevents seedlings from becoming leggy and weak. Seed starting mix is less likely to contain weed seeds and disease organisms, which can be a problem with regular potting mix.

Seed-starting mixes are usually formulated to maintain a more consistent moisture content, which is vital for successful seed germination.

Moisten the seed starting mix before adding it to the containers or cells.

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Sowing Your Cut Flower Garden Seeds

Make holes in each cell using your finger, a dibbler, 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 full. Cover the tray with a light dusting of fine vermiculite or seed starting mix, ensuring all the seeds are covered.

Note: Check the seed packet instructions! Some seeds need light for the germination process and shouldn’t have anything covering the seeds.

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Use Only One Variety Per Cell Tray

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.

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Watering Your Seeds and Young Seedlings

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.

Watering from the bottom allows the roots to be watered thoroughly.

Set the freshly sown seed flats or cells 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.

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Tools to Help Germinate Quickly

Seeds need to be kept warm and moist to germinate rapidly. The use of a heat mat allows bottom heat to get your seeds and will help the germination rate.

Unless the directions on the seed packet state otherwise, set the mat at 65-75° F. You can also put a few trays on top of a radiator.

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 researching which items need to be purchased, this might help. I learned that you might not have to buy as many heat mats and plastic dome covers as you might think.

Once your seeds germinate, you no longer need to use these two items. And because your seeds will be sown at different times depending on the variety (some at eight weeks before the last frost date, some at six weeks), you can move the mat and cover to the next set of seeds you’re ready to start.

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Providing Light

It’s a good idea for seed starts to receive 12-16 hours of light daily for the best results. If seedlings do not have enough light, you will end up with leggy plants.

A grow light is a great idea, especially if you are growing your seeds in a basement or somewhere with little light. If you are using a grow light, it is essential to adjust it to be suspended no more than 3-in. above the top of your plants. Make sure you adjust the lights as the plants grow taller so that they are continually 2-3 inches above the tallest plant.

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Label Your Plants

Label each cell tray or container with the seed variety name and the date sown. It’s extremely important to label your seed trays immediately after sowing.

You would be surprised by how much the seedlings all look the same.

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Run a Fan Indoors for Circulation

Having a fan running in the greenhouse will help with air 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.

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Feeding Your Seed Starts

As the plants grow, they will need to be fed. Add the amount of liquid seaweed and fish emulsion, as stated in the instructions, to your watering can and drench plants weekly.

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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 seedlings from a 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.

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Direct Sow Hardy Annual Seeds in the Cut Flower Garden

Many hardy annuals do not like being transplanted and 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, ensure 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 indoor seed, you can speed up germination for these cold-tolerant varieties, such as Larkspur, by chilling the seeds in a refrigerator or freezer for a week before sowing.

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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 cut flower garden seeds will maintain their viability for up to two years, but the germination rates will decrease over time.

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I know this process can be intimidating for new gardeners, and it still makes me nervous sometimes. But don’t let that keep you from having fun and making this a fun learning process!

You can read all the blog posts in the GROWING A CUT FLOWER GARDEN series HERE.

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I hope this post has gotten you excited about growing a cut flower garden by seed and have a better understanding of where to start.

With these seed-starting basics, you’ll be able to grow healthy seedlings and have the most gorgeous fresh flowers this growing season.

Mistakes are inevitable, but learning and “growing” from your mistakes makes this entire process worth it! Please let me know if you have any questions in the comments below.

Until next time,

Happy Gardening!

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

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