How to Start Flower Seeds Indoors

How to Start Flower Seeds Indoors - Longfield Gardens

Starting flowers from seed is a fun and rewarding experience that can be easily accomplished inside your home. Here are the tools, instructions, and troubleshooting tips needed to grow the flower garden of your dreams.

When to Start Flower Seeds Indoors

Knowing WHEN to start your seeds indoors is the key to having success. Before you begin, gather two important pieces of information.

Your last expected frost date. Find your last expected frost date by entering your zip code here: The Old Farmer’s Almanac Frost Dates by Zip Code. Frost dates vary by geographical location, so it’s important to use information for your specific city rather than copy someone in the same growing zone.  Gardeners with the same hardiness zone, but living in different locations, may have very different first and last frost dates.

The number of weeks needed to establish a transplant of the particular flower being sown. Some flowers such as cosmos grow quickly and produce a transplant in 4 weeks. However, other flowers like snapdragons grow slowly and take 8 weeks to mature into a useable transplant. Research the exact flower you want to grow and how many weeks before the last frost it should be started inside. This information can be found on the back of the seed packet or on the retailer’s website. Then organize your seeds by putting them into groups by number of weeks from sowing to transplanting i.e., 5 weeks, 6 weeks, 8 weeks.

Use a calendar and mark your last frost date as zero. Count back in time and assign each week a number. For example: If your last expected frost is April 25, count back 4 weeks and you arrive on March 28. This is week 4 and the date you should be starting all the seeds that need 4 weeks from sowing to transplanting.

How to Start Flower Seeds Indoors - Longfield Gardens

How to Set Up Your Seed Starting Station

You can start thousands of seedlings inside your home without a fancy greenhouse or expensive lighting system. Here’s everything you need to create an inexpensive seed starting station.

  • 48 cell pack inserts, watertight bottom trays, and humidity domes – one option HERE
  • Heat mat – one option HERE
  • Metal storage rack that’s the same length as your shop light(s). Shelves that are at least 18” wide will accommodate 2 light fixtures – HERE is one option
  • T8 Fluorescent shop light fixture with one cool and one warm T8 fluorescent bulb (Bulbs usually sold separately and available at your local hardware store) One fixture option HERE.
  • Chain and S-hooks for hanging the lights (if not included with the lights)
  • Light timer
  • Professional-grade potting mix – Options include Pro-Mix, Lambert, Frey Professional Planting Mix
  • Seeds
  • Water
  • Plant labels (popsicle sticks work fine)

Place your metal rack near a power source in an area with good air flow and an ambient room temperature of 65-70°F. Hang the shop lights from the rack using chain and S-hooks. On racks where the shelves are 4 ft long and 18 inches wide, you can fit two shop light fixtures (4 bulbs) and 4 trays of seedlings.

How to Start Flower Seeds Indoors - Longfield Gardens

Step-By-Step Instructions for Starting Seeds 

Slowly moisten the growing mix with warm water until it holds together when you make a fist. The soil should be damp but not dripping wet. Fill the cells with soil and then tap the trays on the table to settle the soil and eliminate air pockets. Fill the cells but do not pack the soil.

How to Start Flower Seeds Indoors - Longfield Gardens

Check the back of the seed packet for planting depth. Some seeds need light to germinate while others need darkness. For the ones that need light, place the seeds on the soil surface and press them down with your fingertip to achieve good seed-to-soil contact. For seeds that need darkness, make a hole to the depth noted on the seed packet. Drop one or two seeds into the hole and cover with additional soil. Be sure to label each tray with the flower variety and date sown. Pour an inch of water into the flat tray and allow the cells to wick up water. Once the soil surface is evenly moist dump out any remaining water from the bottom of the tray. Do not allow cells to sit in standing water for an extended period.

How to Start Flower Seeds Indoors - Longfield Gardens

Cover the tray with a humidity dome and place it on a heat mat. You can do this on the light stand or somewhere else. Check daily for signs of sprouting. Once half the tray has germinated, remove the humidity dome and place the tray directly under lights.

How to Start Flower Seeds Indoors - Longfield Gardens

When growing seedlings under florescent lights, it’s important to keep the lights very close to the top of the seedlings — no more than 2-3″ away from the leaves. Lift the lights as the seedlings grow to maintain this distance. Use a timer and run the lights for 14-16 hours each day.

Continue to bottom water as needed to keep the soil evenly moist but never soggy. When the seedlings have one set of true leaves strengthen their foliage by running your hands over them several times a day. If the seedlings begin to outgrow their cells, pot them up into larger containers. Generally, proper seed starting timing should eliminate the need for potting up.

How to Start Flower Seeds Indoors - Longfield Gardens

Harden-off your seedlings before planting them into the garden. This is a fancy term for gradually acclimating young plants to the outside elements. Start the process 1-2 weeks before you intend to transplant seedlings outside. On the first day of hardening off, place the trays in a sheltered spot for 2 hours, and then bring them back inside under lights for the remainder of the day. Increase their time outdoors by an additional hour every day and give them a little more sun and wind exposure as the week progresses.

How to Start Flower Seeds Indoors - Longfield Gardens

Troubleshooting and How to Avoid Problems

You can expect your seed starting success and confidence to grow from one season to the next. Here are a few things to watch out for.

  1. Overwatering. Don’t kill your plants with kindness. Keep the soil moist but never soaking wet. If the soil looks too wet – it IS too wet.
  2. Failure to remove the humidity dome in time. The purpose of a humidity dome is to aid germination. Once 50% of the tray has germinated, immediately remove the dome and put your plants under lights. Leaving the dome on too long invites fungal problems such as “damping off,” which can kill young seedlings.
  3. Lack of light/ improper use of lights. Contrary to popular belief, windows do not provide the necessary light to grow strong, stocky seedlings. Invest in an inexpensive shop light and you’ll see a huge difference in seedling quality. When using fluorescent bulbs always keep the lights 2-3 inches from the top of the seedlings and move them up as the seedlings grow. It may feel like the lights are extremely close to your baby plants, but this is correct. If the lights are too far from the seedlings, the plants will get long and leggy as they reach for the light.
  4. Failure to use bottom heat. If you’re having issues with spotty germination, lack of bottom heat is likely the culprit. Heat mats are affordable and promote consistent germination.

To watch a video from Northlawn Flower Farm on how to start flower seeds indoors, click HERE.

To learn about the differences between annuals, biennials, perennials and bulbs, you may want to read this article on our website:  Starting Flowers from Seeds, Bulbs or Plants.