Seed Starting

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Give your seeds a head start this season.

“The Backyard Gardener” by Kelly Orzel (Lyons Press, 2017) is a comprehensive gardening guide that offers useful advice to help readers build their confidence and know-how. This excerpt from chapter 2 explains how to grow a plant from seed.

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Propagating is my all-time favorite thing to do in the garden — it’s like creating your own little bit of magic in the dirt. At its root, propagating is all about making new plants and increasing your plant stock. It can be achieved in one of three ways: by seed, through cuttings, or by layering. These simple techniques are fun, inexpensive, and rewarding. Certain plants respond better to one method over another. For example, French tarragon should be started with cuttings. It doesn’t come true (or flavorful) to seed, whereas tomatoes and most vegetables grow readily from seed.

Soil And Its Materials

Regardless of which method of propagation you’re employing, there are some materials you cannot do without. Soil, water, pots or trays, labels, a sharp knife, and snips are essential. In addition, bottom heat can speed up germinating and rooting. Most gardeners swear by their secret soilless seed starting mixes, but oftentimes you will be able to find one of these mixes at your local garden center. Traditional all-purpose mixes are wasted on seeds, which carry their own nutrient supply with them. The additional fertilizers can actually inhibit germination and growth. Sterile, soilless mixes offer an economical space for water and air to go and roots to develop without squandering expensive food and fertilizer. Fine bark is just what is sounds like — broken down bark — and you can either generate this on your own by shredding the bark before it’s composted (speeding up decomposition) or purchasing it locally or online. It is light and improves drainage and air circulation. Perlite is expanded volcanic glass that is used for its aeration and drainage capabilities. Vermiculite, made from expanded mica, aids in aeration and drainage, but it is its high water-retentive qualities that differentiate it from perlite. Coarse sand is sometimes used when you want to improve drainage without the added aeration or water retention. Coir and peat moss are made of natural, fibrous material. But while coir is made of coconut hulls, peat is derived from decaying plant material in peat bogs. There is some controversy surrounding peat moss as it takes several millennia to develop and as such is a non-renewable resource. The ratio of ingredients varies from mix to mix, but coir or peat should make up one-third to two-thirds of the mix to make the most of its water- and nutrient-holding qualities.

Seed-Starting Recipe

  • 1 Part fine bark (or screened compost)
  • 1 Part perlite or vermiculite
  • 2 Parts coir or peat moss

To make your own seed-starting medium, toss a combination of compost, fine bark, topsoil, perlite, vermiculite, sand, coir, or peat moss into a large Tupperware bin, wheelbarrow, or dry sink, wet it down so it is the consistency of a wrung-out sponge, and mix. Many gardeners screen their compost, bark, and other materials to achieve a fine blend, but I’ve found that as long as my compost or fine bark is broken down enough (six to eight months), I don’t need to use a sieve. It also ensures that the ammonia is decomposed enough that it won’t harm or inhibit your seedlings’ growth.

Sowing Seed

Almost any plant can be grown from seed regardless of whether it’s an annual, biennial, or perennial. And while there’s nothing wrong with supporting your local garden center, it is substantially cheaper and abundantly more satisfying to grow your plants rather than buy them.

Seeds can be started indoors in trays and pots, or directly in the ground outside, also referred to as in situ. Seeds are programmed to germinate and grow; they come with their own food supply that lasts until they are established enough to produce their own food through photosynthesis. All you need to do is provide favorable conditions and let the seed do its thing. Seeds need water, light, and the right temperature to germinate. Water penetrates the seed coat activating all the metabolic activities inside, and the embryo busts out to release its roots and first leaves. The need for light varies depending on the seed. It’s usually determined by planting depth and whether the seed is covered or not. Some seeds are buried deeper than others, some are scattered on the surface, others enjoy a thin layer of vermiculite over top. The directions for sowing are on each seed packet, but when in doubt the rule of thumb is to plant each seed only as deep as its diameter. Temperature is important for two reasons: it jump-starts germination and root development, and some seeds require a period of exposure to cooler temperatures before they will germinate.

When sowing indoors or early, I prefer to use soil blockers or plug trays to start most of my seeds. It just depends on my mood. Blocking is very soothing and Zen-like, but sometimes I need to sow too much seed, so outcome the seventy-two-cell plug trays. If you are reusing pots or seed trays, you will need to clean them first to ensure there are no lingering fungi or diseases, otherwise your seeds will be dead before they begin. Also, all trays and pots should have drainage holes at the bottom. Using my favorite light seed starting recipe, I firm-in the soil. Do not compact. (Loose soil provides good drainage and air space for roots to tunnel through and anchor to.) Compacted soil inhibits water intake, root development, and aeration. Then scatter or plant your seeds and cover following the instructions on the packet. Some gardeners like to use a dibble to create a planting hole, but a pencil will do the job just as well. To maintain soil moisture, cover each tray with a clear plastic dome; even some cling wrap from the kitchen will do. Additionally, I use heat mats under my flats until the seeds germinate. Consistent bottom heat results in seeds sprouting in as little as half the time! Just remember to remove flats from heating mats once seedlings have emerged, otherwise they can become leggy.

Sowing in situ isn’t much different, but you are more restricted as to when you can plant due to cold temperatures. By using black or clear plastic mulch for two weeks, you can heat the outside soil enough that you may be able to plant earlier if you plan on using some season extension techniques. But the the vast majority of gardeners begin planting once the soil has warmed to 55-60°F, waiting even a bit longer for warm-weather crops like cucumbers and melons. Contact your local agricultural extension office and find out your area’s last frost date, and don’t plant tender seedlings before. Otherwise you’ll become obsessed with the weather forecast and will be running out to protect your new garden from surprise frosts. It’s common to plant in drills down a straight line. Use a pair of sticks and string to map out where you want to plant, then use a dibble, hoe, or shovel to make a shallow V-shaped drill along the line. Water down the new drill, sow seed evenly, space as per packet instructions, and cover with soil. Again, I cannot overemphasize the importance of labeling each drill.

Seeds like baptisia, comfrey, and sweet peas have super hard shells or contain chemical inhibitors that make germination especially difficult. In those cases, you will need to help the process along, and it can be done one of three ways: 1. Soak in warm water for twenty-four hours (no more). 2. Scarify. This involves either scratching the seed coat with sandpaper or nicking the corner before planting to allow water to penetrate. I’ve found that giving a soak after scarifying the seed speeds germination. 3. Stratification. Some seeds need exposure to cold temperatures before they will sprout. To trick the seed into thinking it’s experienced winter, toss the seed packets into a sealed zip lock bag or glass jar, and stick in the refrigerator for a prescribed amount of time. It’s so important to label the bag or jar with the removal date, because as much as you think you will be able to remember when you started the process, you may not. Stratification can last anywhere from two weeks to six months, and the only danger is in removing the seeds from the chilled environment too soon. It never hurts to chill longer. Some seeds will perform even better in the process if mixed with damp sand in the zip lock rather than just the seed packet. Overwatering is the number one cause for seeds not germinating. Too little water isn’t good either, which is why I find it’s best to water from the bottom. This also helps the seedlings develop strong root systems. The tendency to overwater is not the only reason for poor germination. It can also be the result of seeds being buried too deep, the air temperature being too cold, or just impatience. Parsley takes an exceptionally long time to germinate, and every year I question whether it’s going to come in. Of course it always does. So keep the faith!

Once your seedlings are growing, at some point you may see some leaf discoloration and flopping over at the base. This is an indication that they’ve caught a fungal disease, broadly referred to as damping-off. Unfortunately, there is no cure, and you should cut your losses immediately. Do not compost these seedlings — trash them. The best defense against this type of disease is cleanliness. Use clean pots and fresh soil mixes, sow thinly to improve air circulation, and don’t overwater.

As I mentioned earlier, my garden friends know me as “the pincher.” I am ruthless in my thinning and pinching of seedlings. Both of these practices result in healthier, stronger, and more productive plants. Typically you plant more than one seed per pot, cell, or garden bed, and if you’re lucky, more than one will grow. The drawback to keeping all seedlings is overcrowding, which encourages disease and damping-off. It’s vital to remove the weaker seedlings, allowing air to circulate and giving them more room to spread out. I’d suggest thinning in increments, as you’ll find some seedlings naturally die off, are attacked by a pest, or are nibbled on and carried off by a neighboring critter. Cut back at soil level. Once your seedlings have four to six sets of true leaves, it is time to pinch back. You can either use your fingers or some sharp snips to cut out vigorous, center stalks of your plants just above a node and set of leaves. Plants send most of their energy into the development of the main stem and terminal bud, so by pinching it out, all that energy is being redirected back to the roots. This selective pruning encourages branching and side-shoot development, creating a bushier, compact plant that is more productive. You can pinch back multiple times for an even stronger plant if you are feeling adventurous. Once you see the benefits of pinching, you’ll be a believer!

If you’ve raised your seedlings indoors or in a greenhouse, they need to be hardened off before they can be successfully transplanted. This means a gradual exposure to cooler temperature than the seedlings are used to. Place your pots and trays on your porch or deck for a few hours for a couple days, bringing them in at night. Slowly elongate the time spent exposed to the outside temperature, wind, and elements. After two to three weeks the plants should be acclimatized and ready to live outside.

How To Sanitize Your Pots, Trays, and Tools

First, physically remove any dirt and scrub any salt spots. Mix a 10 percent bleach/90 percent water solution in a large tub or garbage can, submerge all pots, and let soak for approximately ten to fifteen minutes. Remove and rinse with water, then let them air-dry. For stone and terracotta pots, rinse and soak in a separate container of clear water for an additional ten to fifteen minutes to remove any remaining bleach from the pot’s pores. Let air-dry.

Soil-Blockers

Photo by Unsplash/
Jen Theodore

These handheld blockers come in different sizes: a large (two-inch) four-block unit and a small (three-quarter-inch) twenty-block unit. These blocks maximize space on your propagation tables and heating mats, in addition to saving money on all those plug trays and pots you won’t be needing. Also, each block is automatically pushed with small depressions for easy sowing.

  1. Mix soil until it has an oatmeal-like consistency.
  2. Insert the blocker into the bin, filling the blocks. Twist against a hard surface until the water flows over the top of the blocker to ensure the blocks come out cleanly.
  3. Press and discharge the blocker into a tray.
  4. Rinse the blocker in a bucket of water between blocking to avoid jamming.
  5. Start sowing!

Heating Mat Hack

Bottom heat speeds up the germination process. A great garden hack is to use incandescent (not LED) outdoor Christmas rope lights under your flats! They will warm, but won’t burn. Then, once germinated, remove your seedlings from the heat source. (Note: Seedlings don’t require as much warmth as seeds.)

Wake Up Your Seeds

Some seeds need a little more TLC before they are ready to break dormancy and germinate. They may require exposure to cold temperatures (mix seeds in a zip lock bag with damp sand and pop in the fridge or freezer for a specific amount of time) or need to be overwintered in the ground to start growing. The latter is often the result of a tough seed coat. Either soak the seed overnight or scarify (scratch with sandpaper or nick with a knife), then soak. The seed should swell, taking in water, and be more likely to germinate once sown.

Testing Seed Viability

Unused seeds should be stored in a cool, dry, dark place if you want to reuse them, as old seed has lower germination rates, or may not germinate at all. To avoid wasting your time and resources, perform a seed viability test in the spring. Place a few seeds on a damp paper towel in an open zip lock bag and expose to the light. Make sure to label which seed is which, and watch over the next couple weeks. You will be able to see if they sprout or not. If you do have success, you can plant the sprouted seeds in pots.

Saving Seed

Collecting and using your own seed is so easy it can become addicting! Let the plant go to flower and wait until the seed head starts to dry (wet seed rots). To harvest, place a paper bag over top of the dried seed head, secure at the base, and cut the stem farther down. Then hang upside down in a cool, dry, dark place for one to two weeks. Once the seed heads are sufficiently dry, take down the stems and shake. You should be rewarded with the sound of delightfully dry seeds puddling at the bottom of the bag. Clean the chaff off any seeds, label, and store in airtight jars, paper seed packets, or envelopes. Keep in your fridge or a cool, dry spot until next year.

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This excerpt is reprinted with permission from The Backyard Gardener by Kelly Orzel, published by Lyons Press, 2017. Buy this book in our store: The Backyard Gardener.