This is a guest post from my wife, who has received several requests to describe her method for starting seeds indoors.
In some parts of the U.S., vegetable and flower seeds can be successfully planted directly into the garden. But in many areas, the growing season is too short to allow this.
Cool spring soil temperatures and cold weather can prevent seeds from germinating or kill young seedlings. If you wait until the weather warms, the plants get off to a late start only to be zapped by fall’s first frost; they don’t get a chance to bear a full crop or to put on a full floral display.
There are three solutions for home gardeners:
- Buy all of your vegetables and flowers as plant starts, once the weather warms.
- Extend the growing season outside with coldframes and rowcovers.
- Start your own seeds inside while the wintry weather lingers.
The first choice is best for beginning gardeners who are working on a small scale. The second option is nice for committed gardeners who want to test the limits. Starting from seed, however, is easy, is cheaper per plant and allows a greater variety of choice among both ornamentals and crops than buying nursery plants.
I’m eager each (early) Spring to get my seeds going. On March 1st, I began seven types of flowers and my basil seeds. (As of March 5th, the basil has sprouted, as have a couple of the flowers.) In two weeks, I’ll start tomatoes and a few others, and the squash, cucumbers and more flowers will follow. How do I do it, and how do I know when to start? Here are my tips:
When should I start my seeds?
In order to decide when to sow your seeds, you need to find the average last frost date for your region. In Oregon’s wet and unpredictable Willamette Valley, published last frost dates range from March 23 to May 14. Based on my own experience, I pick the latter end of this range and count backward from May 1st.
I start my tomato plants six or seven weeks before this date. Slow-to-germinate flowers get an eight-week head start. Squashes and cucumbers don’t transplant especially well, but I germinate them inside to protect them from marauding slugs. I move them outside two weeks later before they’ve developed much of a root system.
What should I plant indoors?
To determine what to plant indoors, read your seed packets. Many will list instructions for both inside and outdoor seed sowing. Knowing which to do will depend on your climate. With flowers, I often do both. I’ll start a limited number indoors for “insurance” and then sow the remainder of the packet directly in the garden once true Spring arrives.
Some crops should not be started indoors because they don’t transplant well or because they need an impractical amount of room. I would not recommend starting the following inside:
- Root, tuber or bulb crops (beets, radishes, turnips, onions, potatoes, carrots, etc.)
- Leafy greens (lettuces, spinach, cabbage, chards)
These cool season plants can withstand planting directly outside even before the weather fully warms. Likewise, things you are going to plant in large numbers should wait until they can be sown into the garden soil. The following are usually grown in sizable quantities:
If you are worried about your short growing season for crops like corn, look for varieties that have a short days-to-maturity period.
Tomatoes and peppers, broccoli, eggplants, cauliflower, melons and squashes can all be started successfully indoors. Herbs and flowers, too, benefit from the controlled environment of indoor seed starting. Let’s get started!
How do I start plants from seed?
The two most important factors for seed germination are temperature and humidity. The seed contains all the nutrients the plant needs to germinate, so it doesn’t need fertilizer or fertile soil.
To start my seeds, I used the bio-dome from Park Seeds, a device that looks like a plastic greenhouse dome with a styrofoam tray. The tray holds little soil-less planting plugs called bio-sponges. Each plug has a hole in it for the seeds. I don’t normally advocate one product over another, but I really like these.
Seeds sprout best in a light soil; don’t use potting soil or garden dirt at this first stage! You can buy seed starting mix or make your own from peat moss, sand, and compost.
Any device that keeps the environment moist and fairly warm will work. You can cover trays of soil with saran wrap or a dry-cleaning bag — poke plastic forks into the soil to hold the plastic layer up off the growing sprouts. Commercial peat pots, yogurt cups or milk cartons (poke drainage holes in the bottoms) or pots made from newspapers (avoid colored ink) all work fine, too.
Set your pots in a tray, tub or rimmed cookie sheet so you can water from the bottom, letting the moisture soak up through the soil. This helps keep the moisture level constant and prevents dislodging seeds with a fountain of water. Do not let the soil dry out! Little tiny seedling rootlets need constant moisture.
Seeds vary widely in size. I like to use tweezers to place them exactly where I want them. In general, seeds should be planted approximately four times deeper than their diameter. Some seeds need light to germinate and should be scattered just on the surface of the soil. Again, read those packets!
I usually put two seeds into each hole. I use three if I think the germination rate will be low. You can test your germination rate by placing ten seeds between layers of moist paper towels in putting them in a Ziploc bag in a warm place. This is a good idea if you have saved the seeds yourself or they are several years old. Do this 2-3 weeks before you want to actually start your seeds.
As you’re planting, take good notes! Make a planting diagram and jot down how many days it takes each type of seed to germinate. Some germination times are given as huge ranges (5-20 days). The happier the seed is (warm and wet), the speedier germination may be.
If you are using individual pots, mark them with labels or masking tape, unless you know for sure that you will recognize what the leaves of your young plants will look like. There’s nothing worse than getting your plants mixed up. This is especially important if you are starting different varieties of the same crop! Free plant stakes can be made simply by cutting up a plastic yogurt tub. Store your leftover seeds in a ziploc bag or glass jar in the refrigerator.
Now that the seeds are snug in their beds, cover them to retain moisture and put them in a warm place. A temperature of 70 degrees Fahrenheit (21 degrees Celsius) is ideal, but in March our house is nowhere near 70 degrees! I like to set my mini-greenhouse on a heating pad (a wet/dry safe heating pad set on low) to maintain a more constant temperature, since our thermostat drops to 54 degrees (12 Celsius) at night. Some people recommend putting the seed tray on top of the refrigerator. If your house is more temperate, the heat source is unnecessary. I have often started seeds without a heat source, but peppers and eggplants seem especially fussy about the temperature.
What happens after the seeds sprout?
Once the seeds have germinated (keep them moist!), they’ll need light, nutrients and air. Give them some ventilation and move them to a very sunny window, supplemented with artificial light. There is no need to buy an expensive grow light or full spectrum light. For these purposes, a basic 48″ fluorescent shop light is all you need.
As your plants grow, keep the light about 6″ from their tops. If the light is too far away, the plants will grow spindly as they stretch for it. This can be rather tricky if you are starting different types of seeds at the same time, because they will grow at varied rates. You can lift the shorter ones with shoeboxes or phonebooks to alleviate this difficulty. Once all the seeds in your tray have germinated, remove the cover completely. Too much humidity at this stage can encourage mildew and harm the seedlings.
As you water, fertilize with a weak solution of water-soluble all-purpose fertilizer. I make mine about one-quarter the strength called for. Watch out for crystallized salts forming on your soil surface — that’s a sign you’re over-fertilizing and need to cut back. Turn the lights off for your plants at night (they need a dark cycle to grow properly) but leave the heat on (temperature fluctuations can stunt them).
What about transplanting?
When the seedlings first sprout, they will usually have a pair of first leaves that look nothing like the true leaves that come later. (Many crops are dicots, but not all.) Watch closely, and soon after they have two sets of true leaves, it’s time to move the teenage seedlings into their first real apartment. Water your seedlings thoroughly an hour or two ahead of time, and then, working carefully and quickly, remove each seedling into its own pot.
At this point I generally use an all-purpose potting soil. Scooping them up from below, try your best to get all their little roots, and handle their tops as little as possible, and always by the leaves, rather than the stem. A damaged leaf can be replaced; a damaged stem often dooms a plant at this stage.
Depending on how long your plants will be living inside, you may perform only one transplant, or you may need two. For my tomatoes, I’ll move them into 4-inch plastic nursery pots first, then into gallon-sized pots before they go outside. Everything else gets one transplant, then into the garden.
Once your seedlings are thriving, it’s tempting to treat them a bit too carelessly. Being started inside in a safe environment, they can’t stand the shock of an immediate change in their conditions. Basically, they are weak, coddled little things. Expose them gradually to the out-of-doors by setting them outside on nice days for a few hours, being sure to bring them inside at night and making sure they don’t get sunburned or blown over. Some gardeners like to have a fan blow on their indoor starts, saying it strengthens the stems to withstand windy outdoor conditions. I can’t vouch for that, but I do think it helps prevent mildew.
Wow, that seems like a lot of work when I write it all out. But it’s not really! Watching my garden plants grow from tiny seeds is a thrill every year. I love trying new things each spring and learning from my successes and failures. I hope these tips get you well on your way to learning what works best for you. Happy gardening!