This content originally appeared in IPR's Garden Variety newsletter, which brings together Iowa's gardening community for expert advice and timely tips for gardeners at all levels year-round.
For any gardener, seasoned or aspiring, the first step to starting seeds is creating a schedule. Different plants will have different growing times, so check the back of your seed packet for specific information. Once you’ve identified how many weeks it will take your plants to grow before they’re ready for transplanting, count backward from Mother’s Day and you’ll have your planting date!
Plan to start your seeds with Mother's Day in mind
The average last frost date for most of Iowa is somewhere between May 10 and May 15. This period of time, when it’s staying 40 degrees and above at night, is an ideal time to transplant your seedlings outside. Most popular plants need four to eight weeks of growing time before they’re ready for transplant, which means you’ll likely start your seeds sometime between March and mid-April.
Get started on growing your seeds indoors
Container
Your container can be pretty much anything — a store-bought seed flat, a recycled yogurt cup — as long as it isn’t too deep. It should be about two inches deep and will need a drainage hole.
Medium
Medium is a fancy name for the soil you’ll be planting your seeds in. Experts recommend buying something lightweight, porous, and free of pathogens. That can be a pasteurized seed starting mix or fine grade vermiculite (a naturally occurring mineral that retains nutrients and moisture).
The finer texture of these mediums will provide better soil-to-seed contact, and pasteurization (a process in which the soil is heated to about 180 degrees) destroys weed seeds and disease organisms.
Planting
Fill the container with soil until there’s about an inch left at the top. Pack down the soil, water thoroughly and allow your container to drain. Finer seeds or seeds that require light for germination need to be planted on the top of your soil container.
Lightly press the seeds into the soil and then cover them with a thin layer of soil (about one to two times the seed’s diameter.)
Temperature
The ambient temperature of your home during the colder months will be perfectly fine for your little seeds as long as they have a good, warm base — around 70–75 degrees. If you’re in a colder space,you can get seed-heating mats from most garden centers.
Or, DIY it: Putting your seeds on top of a vent or radiator will also help to keep their root zone warm.
You can also place plastic wrap or some sort of clear cover on your containers to trap moisture and heat — essentially creating a mini-greenhouse.
Lighting
Seedlings need plenty of light, and you might consider setting up a specialty lighting system depending on your home set up.
Seedlings should be placed in bright, indirect light as they germinate. Once the seeds have germinated — you can tell by sprouts poking through the soil — you should move them to an area with direct sun and slightly cooler temperatures.
Setting up lighting can be a feat of engineering, but bright, even light is key to good growth for your baby plants. Horticulturist Aaron Steil recommends using a four foot plug-in shop light with two fluorescent bulbs — one cool white and one warm. LEDs and grow lights work too, but avoid incandescent bulbs as they’ll dry out the plants.
Regardless of which light source you choose, you should keep it six inches from the top of your seedlings at all times. The easiest way to achieve this is to set your seed trays on some sort of stack or pallet and remove items as the plants grow to keep your tray at a fixed height relative to the lights.
If you don’t want to set up a lighting system, you can take advantage of natural light in your home. This may increase your chance of running into issues, including spindly growth, or you might have less success in germination, but you’re still likely to produce transplants. For the best chance at success, set your plants up in the window that gets the most light in your home.
Watering
Every growing plant needs water. After you’ve sown your seeds, be sure to moisten the germination medium immediately. The goal is to have constant moisture in the root zone.
For regular watering, a misting nozzle or spray bottle used at the top of the seedlings works well. Another good option is to submerge the bottom of the container in water to allow the plant to take in water from the roots up.
Maintain humidity: A clear plastic cover or food wrap over your seedlings can help keep in moisture. Once your seeds have germinated you should take this covering off and wait until the soil dries out to water again to avoid oversaturation.
Common problems when starting seeds indoors
After setting all this up, you’ll be well on your way to gorgeous flowers and yummy veggies. To make sure your seedlings reach the finish line, keep an eye out for two common problems:
Too much moisture, or “damping off”
Damping off is a fungal disease that can quickly wipe out an entire tray of seedlings. While clear covers keep the soil from drying out, they can also trap too much moisture. Be conscious of how humid it’s getting under your cover and take it off if it appears too damp.
Weak seedlings, or “spindly growth”
Lanky, spindly seedlings are harder to successfully transplant than stockier ones. This problem generally occurs if you’ve started your seeds too early (remember to make that schedule!) or they aren’t getting enough light.
When growing seedlings in a windowsill, they will naturally stretch toward the light. Try to place seedlings by south-facing windows and rotate them every time you water them to prevent them from growing to one side.
Exposing your seedlings to a little bit of simulated wind movement can also help make them sturdier. There are a few ways to achieve this: Set up a fan that doesn’t point directly at the leaves, but still moves them, or petting your plants. Give them a gentle brush with the palm of your hand to show them you care about their growth.
Need help picking the right seed for you? Check out our guides on garden design and selecting seeds.
If you’re new to gardening, don’t let these potential problems put you off. With good light, careful watering, and a whole lot of patience, your seedlings can thrive. Before you know it, you’ll be filling your garden with all your hard work!
