General Seed Starting Guide
Before you begin:
Find out your last frost date, based on your location. The Farmers Almanac has a simple look-up tool online here.
Each type of seed should be started a different number of weeks before your last frost date. For example if you live near me in Olympia, and are starting cosmos seeds, which should be started 4 weeks before last frost, you would count back 4 weeks from our last frost in the first week of May and start your cosmos seeds in the first week of April.
Cosmos: Start indoors 4-6 weeks before last frost
Celosia: Start indoors 6-8 weeks before last frost
Larkspur: Direct seed in the fall, or start indoors 6 weeks before last frost. If seeds don’t germinate, check out this fantastic guide to starting Larkspur seed which recommends “Place[ing] seeds sandwiched between sheets of moist paper towel in a bag or food container in fridge for 36 hours, then sow” which resulted in 90% germination rate after 11 days and no change after that.
Clary Sage: Start indoors 5-7 weeks before last frost. Press seeds gently into the surface of the potting soil but do not cover— light is required for germination.
Seline Blushing Lanterns: Start indoors 8-10 weeks before last frost
Scabiosa: Start indoors 4-6 weeks before last frost. Sow 2 seeds per cell, pressing seeds gently into the surface of the potting soil and barely cover— light aids germination.
Snapdragon (cool season varieties): 8-10 weeks before planting out, prinkle seeds onto prepared potting soil surface but do not cover— light is required for germination. Gently mist, or bottom water to prevent burying the tiny seeds. Plant out 8 weeks before last frost and protect from hard freeze with frost cloth. Can re-bloom in the fall if kept healthy through the summer.
2. Gather your tools and materials
There is lots of opportunity to reuse materials, and get creative to use what you have on hand. If you don’ t have something on this list or can’t afford it, don’t worry, with some patience and creativity you can make it work. Here are the tools I use, and some ideas for alternatives. I’ve bolded the tools that are most important for success:
High quality germination or potting soil— This is non-negotiable. Look for finely textured, well draining potting soil marketed for seed starting. I use Sunshine Mix 4.
72 cell seed starting inserts (or ask local nursery departments for freebies), closed bottom trays (or cookie sheets, lunch trays), and clear humidity domes (or plastic bag)
3.5-4” nursery pots (or red solo cups)
Electric heat mat (or a space heater in a warm room or closet)
Grow light— I use cheap LED shop light (bar shape) hung from the ceiling or shelf above on bailing twine, it doesn’t have to be fancy! A goose neck lamp could also work. A bright windowsill is a last resort.
Plant labels— No need to buy new. Popsicle sticks or yogurt containers cut into strips work great. Use a garden marker, or a soft graphite pencil, regular sharpie will wear off.
3. Clean your tools— Cleaning seed starting pots, trays and domes is incredibly important to prevent fungal diseases and rusts, which can easily wipe out entire trays of seedlings. Scrub your trays, inserts, pots and domes with hot soppy water, or soak them in a 10% bleach solution.
4. Make a plan for up-potting or planting out
What will you do when your seedlings outgrow their 72 cell tray, before it is warm enough to safely plant outside?
Each seedlings sown into 72 cell trays will need to be up-potted to 3-4” pots when you can see roots at the bottom of the 72 cell tray. Keeping a seedling in a small tray will seriously stunt it, and even after you plant it outside it will be slow growing and often fail to thrive.
If you have access to a greenhouse, transitioning your seedlings in 3-4” pots into the greenhouse is a great idea to save space in your indoor germination station, and gradually introduce your seedlings to outside life.
If you don’t have a greenhouse, and can’t keep all of your 3-4” pots under your grow lights inside, you will need to make a plan. Here are some potential ideas:
1) Direct sow seeds rather than starting them indoors
2) Start seeds 2 weeks later than recommended and plant your 72 cell plugs outside,
3) If you’re within a week or two of being able to plant out, every day move your 3-4” pots outside during the day, and inside at night,
4) Buy greenhouse plastic and rig up a small temporary enclosure for your seedlings outside in the sun,
5) Plant out your seedlings outdoors and cover them with protective frost cloth.
Now you’re ready to get sowing!
Fill 4” pots, or seed starting trays with high quality potting mix that has been lightly hydrated. It should feel moist, not powdery or saturated.
Some seeds must be surface sown, others need to be buried in the dirt. Unless otherwise noted, plant seeds twice as deep as the seed is tall on it’s longest side. Place 1-2 seeds per hole and cover lightly with soil. Keep cell packs or pots in seed starting tray.
Cover for a few days with clear plastic dome lid, or plastic bag to speed germination. If you have seed starting heat mats, most seedlings will appreciate them. Place trays under bright grow-lights, keeping seedlings about 4” from light, or in a greenhouse environment. Remove cover once first set of leaves emerge. Monitor and water as needed, allowing top layer of soil to dry between watering. If growing in seed starting trays and seedlings roots have reached the bottom of the tray, or have stopped growing before all risk of frost has passed, transplant seedlings into 4” pots and continue growing indoors or move into a greenhouse environment.
Unless variety is known to tolerate cold, plant out into garden after all risk of frost has passed. Choose a location with full sun, well drained soil and consistent irrigation or ability to consistently hose water. Space your seedlings 6-18” apart depending on the size of the plant. If your plant will grow taller than 3’, place a tall stake next to (or tomato cage over) your seedling at planting.
Some plants require pinching. Google your variety. If pinching, do so when plants are 8-12” tall by cutting the plant down to 6-8” tall, cutting just above a set of leaves. This will force the plant to branch from the base and produce more flowers on longer stems.
Tie the plant to stake as it grows to keep it upright. Always monitor for drought stress and water as needed. For best results, water deeply 1-2 times a week during the dry season.