Hands down seed starting is what generates the most questions, I had my own struggles when I was getting started so I understand the frustration and challenges. Below find the most common questions and issues I hear about.
- When to start the seeds? When to start is based on when the transplant should be planted outdoors in the garden. Knowing when to plant outdoors gives you the target time to count backwards from to start the seeds indoors. With soil blocking we start seeds 2-6 weeks before it’s time to plant outdoors depending on the specific plant. The general rule of when to plant is based on nighttime temperatures, daytime temperatures don’t matter as much.
- Warm-season tender annuals (like tomatoes, zinnias, and basil) can be planted outdoors when nighttime temperatures are at 60 degrees and warmer, typically 2-3 weeks after the last spring expected frost.
- Cool-season hardy annuals (like broccoli, parsley, and snapdragons) can be planted outdoors when nighttime temperatures are below 60 degrees and cooler. Warmer at night inhibits thriving and would also indicate even warmer days which this family of plants really don’t like.
- When are transplants ready to plant outdoors? A 3-5” tall transplant to go to the garden is best. How long it takes to get that size plant depends on the individual plants type of growth habit and the growing conditions. If trying to grow warm-season tender annuals in a room temperature below 70 degrees they will barely grow. The indoor growing conditions should be conducive to that type of plant’s preferred conditions.
- Do you cover the seed with soil or not? Seed packets should indicate if a seed needs light or darkness to sprout, if not ask a search engine. For those that need light to sprout firmly seat the seed on the surface and do not cover. Those seeds that need darkness should be covered with soil and in soil blocks that is done by pushing them deeper into the block with the toothpick.
- Seeds are dead when you start: Be sure your seeds are viable (ask a search engine how.) Oftentimes seeds stored in hot-to-warm humid conditions, gathered from one’s own garden incorrectly or purchased from a retail source that have stored incorrectly (hot warehouses, etc.) have died. I experienced this years ago with seeds purchased from a local big box store, good seed brand, easy to start seeds—all dead when I brought home. Buying seeds from a garden type store is best because they typically provide the conditions needed to keep seeds viable.
- Planting seeds directly in the garden when they prefer to be started indoors: Every seed has a preferred method of starting life. This translates into the easiest and most successful way for seeds to sprout and grow into a plant. If you don’t know which way the seed you have prefers, enter sowing instructions into a search engine.
- Skipping a seedling heat mat: Perhaps the leading cause of poor sprouting and survival of seedlings indoors is cool soil. Most seeds sprout at 75 to 85 degrees. Soil temperature runs approximately 15 to 20 degrees cooler than the surrounding room temperature. If your house temperature hoovers at 70 degrees that means that the soil is around 55 degrees. A seedling heat mats is a small investment when you consider your efforts and how many seeds you are losing. Both cool-season and warm-season seeds need consistent warmth to sprout.
- No grow light: Plants indoors need 16 hours a day to grow into a healthy transplant. We don’t have 16 hours of natural sunlight a day. When plants don’t get enough light they start stretching and looking for it. This is the cause of tall lanky plants; they stretch as they search for light. Short stocky healthy plants are grown under lights ,are more resistant to diseases and pests and are just healthier all around which leads to more production.
- Poor sprouting indoors. I still have this happen from time to time. If you are starting with viable seeds the cause of poor sprouting is typically operator error. If the seeds have been planted properly (like prefers to be started indoors, seed covered or not covered per instructions, etc.) I find that temperature is the main problem for me. Either the heat mat is too warm or not warm enough for that specific group of seeds or the air temperature is either too warm or cool. Example is when we are starting cool-season hardy annuals like snapdragons in late summer for fall planting to winter over and bloom in spring. It is usually warm to hot outdoors at the seed starting time which tends to overheat our grow room air temperature and snaps will not sprout under those conditions. Our solution is to leave the room door open and this lowers the air temp to 65-70 degrees which is ideal for snaps and they sprout in 7-10 days. If trays have sat on a heat mat for longer than 14 days without sprouting I would move off the heat mat to a cooler spot under lights if available, water and see if a cool down forces them to sprout. I would restart and change the conditions previously provided. Over watering can also be a cause. Seed starting soil mix should be thoroughly watered each morning and 24 hours later the blocks should be somewhat dry when it is time to water again. Adjust air temperatures to make this happen. The cycle of wet to dry is part of the natural cycle of sprouting, if wet all the time seeds will rot.
- What’s your question?
I hope this helps clear the way to a successful seed-starting year!
My online course Seed Starting Made Easy is a 90 minute course that covers seed starting indoors using soil blocking and how to plant seeds outdoors in the garden. Check it out and read some student reviews here.
Founder of The Gardener’s Workshop and Flower Farming School Online. Award-winning Author of Vegetables Love Flowers and Cool Flowers. Watch Lisa’s Story and view her blog Field & Garden. Connect with Lisa on Facebook and Instagram!