Think Like a Seed
What do seeds need to sprout and thrive? The ancient elements of air, water, earth, and fire (heat and light), in the right balance and at the right time. If you understand plants’ needs, you can intuitively feel what to do.
Here’s what happens when you plant a seed: Each seed has a living plant inside, called the germ. It’s alive, but asleep. The germ is protected by a hard seed coat, and provided with food in the form of hard nuggets of starch. This embryonic plant is dormant (French for “sleeping”) until water, warmth, and light wake it up. The seed absorbs water from the soil, swells, bursts the seed coat, and starts to grow.
As soon as the germ wakes up, it makes a root. It senses which way is up, and extends the root downwards. Only after the root is established does it make a stem and start to grow upward. The starchy part of the seed, the fuel, sits on top of the new stem and turns green when it reaches the light. This is the cotyledon. It looks like a leaf, but it’s actually the starchy part of the seed. It feeds the plant until the true leaves emerge.
Seeds need water to break dormancy, soften the seed coat, and hydrate the inside of the seed. The water in moist soil is enough for vegetable seeds. Too much water is a problem, so go easy. Soil should be moist, not soggy, for both seeds and plants.
Instead of a hard seed coat, some vegetable seeds have natural chemicals on the outside that prevent sprouting. These germination inhibitors are nature’s way of making sure the seed doesn’t sprout too soon, when there isn’t enough water for a plant to grow. The umbel family–carrots, parsnips, parsley, cilantro, fennel, and dill–all have inhibitors. Beets, chard, and spinach have milder inhibitors. These seeds will all sprout much faster if you soak them for 2 to 4 hours, rinse them well under the tap (in a strainer!) and plant them while still wet.
Plants need air, like we do. Seeds that sit more than a few hours in water will rot and die. That’s why a good potting mix is fluffy, to let in air. Organic matter, mulch, and no-till techniques all build soil structure with lots of air spaces from worms and other soil life. If the soil is soggy, water fills all the spaces between soil particles and the roots die from suffocation. Root rot, wilting, and damping off (plants fall over at soil level) can all be symptoms of too much water. After seeds have sprouted, it’s best to let the surface dry a bit between waterings. Moving air is best–plants, like us, get weak if they don’t move.. If plants will be in pots long, put a fan near (not directly on) them.
You may need to ensure more heat for your seedlings than the surrounding air. Starting in the house ensures reasonably warm temperatures, although moist soil will be about 10 degrees colder than the air, so heat mats speed things up. In a greenhouse, heat mats help a lot and are more fuel-efficient than heating the entire space. You can also add heat by using a hot frame, which is a compost pile (or wet wood chips) covered with soil and enclosed to hold in heat. Plant into soil on top of the pile, or place flats of seedlings directly on the pile.
Each seed has a minimum sprouting temperature. Asian greens, mache, and miners lettuce sprout just above freezing. Carrots, spinach, lettuce, mustard, beets, turnips and radishes sprout at about 55 degrees. Kale, broccoli, and cabbage withstand a lot of cold as plants, but the seeds sprout best in warm (70-80 degree) soil. In nature, the cabbage family stands through the winter and drops seeds in late summer, so start them warm, then put them outside a month before last frost. If your tomatoes do fine, but your peppers are stunted or sluggish, that’s because peppers need more heat. Eggplants, okra, and melons, which hail from India and Africa, need even more.
The rhythm of light and dark is a powerful force on plants. It dictates how to plant: Many seeds cannot sprout unless they sense some light–these need planting near the surface, or even on it. Others that need dark we bury deep. The effect of light on a plant’s life cycle can dictate when to plant, too. Onions are very day-length-sensitive. They are planted in late winter or very early spring so that when the long days of midsummer trigger bulbing, the plant is big enough to make a good bulb. Many plants flower or bear fruit when days lengthen or shorten to a certain point. Planting greens when days are short and cold in spring and fall keeps them in vegetative growth, so we get lots of leaves rather than tough stems.
Vegetables and flowers need bright light–more than normal home lighting provides. (House plants are usually jungle or forest plants used to very dim light.) The most protected and controlled environment is indoors with lights. You don’t need special grow lights. A cheap plug-in “shop light” with fluorescent or LED tubes is great. With regular home shop lights, the plants should be 6-8” from the light. Stretched-out plants are too far away. Bleached or shriveled leaves are too close. The proverbial sunny windowsill can work, but it can also dry out seed trays and bake tiny plants before you know it. If using a south window, use larger pots that can stay moist longer, and monitor conditions carefully. Most plants need darkness at night. The outdoor light of a greenhouse or cold frame is most natural., but then you will need to ensure enough heat.
While plants need air, they also need the firm embrace of the soil around them. Firming the soil after planting ensures that water can get to the seeds from below by capillary action. It holds the seeds in place so they can orient themselves and send roots downward. A major cause of seed failure is when seeds shift position each time they’re watered, so they exhaust their food supply before they can root.
Seeds and plants do best in living soil. Beneficial fungi and bacteria form symbiotic relationships with plants as the seeds start to sprout. They help the roots find water, make more nutrients available, and prevent diseases while the seedlings are still small. I use potting soil that has compost and worm castings mixed in. A handful of forest soil or some fungal inoculant helps as well. Sterile seed-starting mix is often suggested in books, but in my experience, diseases and problems proliferate in sterile mix, because it's a vacuum waiting to be filled, and pathogens fill it quickly. Instead, give your seeds a healthy living soil from the start.
I hear gardeners fretting all the time about planting too late, but planting too soon is a problem too. If you like to gamble on early planting, fine. But the biggest, most reliable yields come from planting when the time is right. So learn to read the clues and not just the calendar. Wait for the oaks to leaf out before planting your main peas and lettuce. Listen for the frogs in spring and the crickets in summer. They live right on the soil, and feel its warmth–or not.
The size of the seed, the quality of the soil, and the temperature dictate the timing for fertilization and transplant. Since the food stored in the cotyledon feeds the seedling at first, you don’t need to feed your seedlings during germination and establishment. After the seedling has 2 pairs of true leaves, you can water it with a mild fertilizer like compost tea. A quality potting mix should have nutrients for about 3 weeks to a month of growth.
What type of containers to use for seed-starting depends on space available, but even more on your time. If you putter in the greenhouse every day, you can save space and soil by starting seeds in trays and lifting the tiny seedlings into their own pots when they get a true leaf. You can maximize your space by using trays with many small modules. Or use egg cartons and yogurt pots, because you’re watching them carefully. But for busy people who may not be able to check during the day, it’s safer to use larger pots of consistent size. I use 3” pots and rectangular trays that fit a heat mat and allow watering from below. Larger pots give you more time before the seedlings get rootbound, allowing latitude for delays.
There’s an interplay between water, air, soil, heat, and light. Each is important, but not at the expense of the others. Disaster happens when one factor is allowed to eclipse the others, like when over-enthusiastic watering drives all the air from the soil. Or when the need for light leads plants to dry out in a hot window or languish in a cold greenhouse.
If you understand these needs, you will develop a feel for what they are getting too little of, or too much. This is a green thumb--the human mind and hand in sympathy with the growing plant.
Jamie Chevalier lives and gardens on a river in the Coast Range of Northern California. She has gardened professionally in Alaska and California, as well as living in a remote cabin, commercial fishing, and working with seeds. She is the proprietor of Quail Seeds.