Indoor Seed Starting 101

Starting seeds at home is a fulfilling part of getting your garden started on the right foot! When you grow your own transplants you:

• Get precise plantings with less seed
• Grow healthier plants than the starts at the hardware store
• Extend your season and get larger yields
• Reduce weed competition

What vegetables should I start indoors for transplant, and what should I direct-seed?

Root crops like carrots or radishes are usually direct-sown outdoors. Many other veggie types like sweet corn, cucumbers, summer squash, kale, and dill can be sown directly with as much success as transplanting; here the choice is yours. Tomatoes, peppers, eggplant, broccoli, and other heading cabbage-family crops should typically be started indoors and transplanted, since they take a long time to mature and will yield earlier and more successfully if started early.

When should I start seeds for transplants?

• Estimate how many weeks it will take your seedlings to grow big enough for transplant. Generally, cabbage family plants will take 4-6 weeks to reach transplant size, while tomatoes, peppers, and eggplant should have 8 weeks to grow before transplanting. 
• Decide when you would like to plant your starts outside. The key factor in knowing when to plant outside is your area's average last frost date. For most areas, a quick google search will turn up that information. But, gardeners in the mountains should note that last frost dates can vary by as much as a month within the same county depending on elevation - check with your local extension agent to be sure. Cabbage family crops and some herbs can be planted outside two or three weeks before the last frost, but tomatoes, peppers, and eggplant are not frost-tolerant at all, and should be planted a week after the average last frost.
• Count backwards from your desired planting date the number of weeks it takes to grow the seedlings. For example, if you would like to plant tomatoes on May 27th, count back 8 weeks. You should start them no later than April 1st.

Transplant Timing Reference Chart

How to Choose a Seed-Starting Medium

There are many organic soil mixes on the market for everything from houseplants to vegetable plants. For a beginning gardener, buying a mix specifically for seed starting is an easy way to start growing transplants. Use the high quality (but often pricier) mix for seed starting in small cells and the more economical potting mix for filling in large containers if you'll be moving your transplants to pots. If you’re an experienced grower, you may want to start making your own mix. Check out Elliot Coleman’s The New Organic Grower or Barbara Ellis’ Starting Seeds for good recipes. 

Glossary of Common Terms on Soil Bags

Compost – Decayed organic matter which can come from many sources (kitchen scraps, mushroom logs, cow or worm poop, etc.). Full of great nutrients and beneficial microbial activity!

Sphagnum Peat Moss – Decayed and dried moss that has been harvested from peat bogs with excellent water retention. Note: peat moss has recently fallen out of favor because it is not very sustainable. Look for mixes containing coconut coir (a renewable resource) instead.

Coconut Coir – The brown fibers that make up the husk of a coconut. Often sold ground and compressed as an alternative to peat moss.

Perlite – Puffed-up volcanic glass (think Rice Crispies, but rocks). Low water retention and excellent for soil aeration.

Gypsum – A commonly-mined mineral added to soil mixes as a fertilizer and soil conditioner

Vermiculite – A commonly-mined mineral that looks like mica. The unique shape allows for good water drainage while catching nutrients.

How to Germinate Seeds Indoors

Choose your containers: People use everything from egg cartons to cups made of rolled newspaper, yogurt cups to horticultural flats. All containers must have good drainage and be sanitary. If you are reusing containers seasonally, be sure to wash them well and rinse in a 1:4 bleach solution, then air dry. Drainage is important; if kept too wet, young plants will be susceptible to ‘damping off,’ ie infection by any of several fungal foes that will decimate young plants easily.

Sow the seeds: Most seeds do fine lightly pressed into the soil. A good rule of thumb is to plant the seed as deep as it is long (so bean seeds can be planted deeper than spinach seeds). Very small seeds can be sown on the surface and then lightly sprinkled with soil mix or pure vermiculite

Special treatment: Most seeds will germinate just fine when simply planted in soil and watered, but some need special treatment to spur germination. Check the planting instructions on the seed packet. 

• Scarification: Scratching the seed coat to allow more water in. This usually is done by scratching the seeds against coarse sandpaper. Ex: Nasturtiums
• Stratification or freeze treating: Some seeds need to experience a cold period of winter weather before germinating. You can fake this by placing seeds in the refrigerator or freezer before planting. Ex: Echinacea
• Light sensitivity: Many seeds are not picky, but some need to be surface-sown to expose them to light, like lettuce.
• Pre-soaking: Some seeds have naturally low germination that can be improved by pre-soaking. Soak seeds in water for 24 hrs and then plant immediately. Ex: spinach, parsley, okra
• Heat: Most seeds will germinate best at about 80⁰F, which means they do best at temperatures warmer than room temp. A heating mat or room with a space heater will help keep them warm until emergence.

Watering During Seed Germination

During the first week or two, while the seeds are germinating, the soil should stay moist but not soaked. This is best done by misting the surface, rather than using a watering can, and keeping the containers covered with a plastic lid, plastic wrap, row cover or a pane of glass to increase humidity until germination occurs. Once seeds germinate remove the plastic cover to prevent damping off.

Caring for Seedlings

Light: Once the seedlings have germinated, they should be placed in bright light or under grow lights to prevent them from becoming "leggy," which happens when the stems grow faster than the rest of the plant, making the seedlings weak and unstable. Special “grow lights” emit more light from the part of the spectrum most used by plants. However, they are pricey and many home growers do just fine with one warm and one cool bulb, or just plain florescent lights. The most important thing is that seedlings get enough light – 14 to 16 hours per day.

Airflow and humidity: The most often overlooked part of caring for seedlings is good air flow to prevent damping off. Placing a fan running at low speed near your seedlings can help a great deal. Water plants regularly, but take care not leave the soil surface constantly saturated. Once the seedlings have all emerged, the soil surface should be allowed to dry out between watering. A good way to minimize overwatering/excessive dampness is to water early in the day and allow the plants to dry off before nightfall. 

Stepping up: If you have started seeds in small germination containers or flats, they can be “stepped up” into larger containers once the young plants have at least their second set of true leaves. Once stepped up, a dilute fertilizer may be applied if necessary, but check your soil mix to see if it already contains fertilizer. If not, fish emulsion or compost tea works well but follow the directions for seedlings on the label so you don’t "burn" the plants with too much nitrogen at once.

Hardening Off: Hardening off is a process by which plants are prepared to manage the harsher conditions of life outside. It consists of decreasing water and fertilizer 1 to 2 weeks prior to transplanting outdoors, and giving the plants some time outside. This allows the cellular structure of the plant to ‘harden’ - literally, the cuticle of the plant hardens to provide protection against the harsh rays of the sun and desiccating winds. Move your plants outside for a few hours daily for the last couple weeks before transplanting. Be sure to place them in a shady protected place and allow them to adapt slowly. Be attentive to watering, since plants outdoors can lose water and quickly dry out. The plants should not be fertilized and will not grow rapidly during this transition. Their energy is being utilized elsewhere.

Transplanting

Once well hardened-off, the plants are ready to set out into the garden! Prepare your soil well, plant gently, and always, always, always water them in (well!) with perhaps a light application of fertilizer. You’ll get the satisfaction of seeing your faithfully tended plants thrive!

	Article Written by: Leah Smith
	About the Author: Leah Smith is the Seed Product Manager at Sow True Seed, where she focuses on adding new varieties to the catalog and ensuring the seed stock is top-notch. Her firsthand experience in farming has given her a deep understanding of cultivating crops while caring for the environment.