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Seed Germination

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It all starts with a humble seed…

Seeds are truly magical. They are organic logic bombs, containing everything a plant needs to grow and reproduce.  Although a large part of indoor plant propagation focuses on cloning, another part includes growing plants from seeds. And this is where indoor gardening takes on a nice spin, because a grower can cultivate plants that are as unique as the parent plants.

Seeds can be germinated in many different substrates. Each medium has particular qualities that will ether enable or hinder adequate germination and growth, and so growers must familiarize themselves with their medium of choice in order to ensure high germination and seedling success rates. Although many choose to germinate seeds in potting soil, I find most to be too nutrient rich and/or too dense for seedlings. The medium of choice for seedling propagation must be light, porous, inert (or with a low nutrient content), and must provide a root zone with a well-balanced air-to-water ratio.

coco_coirCoco coir – Coco coir is my favorite substrate when growing from seed. Roots seem to go crazy in coco! It can be used to germinate seeds in small planters, trays, or cups. Coir provides a good air-to-water ratio and is less likely to waterlog than peat based potting soils. I would, however, shake off any excess water from planters or cells before planting seeds in coco.

Rockwool_cubesRockwool cubes – Rock wool cubes provide an excellent foundation for growers who plan to grow their plants in rock wool blocks or slabs. They are also widely used for plants that will later be transplanted in media such as LECA (clay pebbles), coco chips, or silica rocks. It is a neutral substrate (pH 7), so requires pre-buffering in water with a pH of 5.5 before use. Rock wool cubes need to be presoaked and the excess water expelled, either by shaking off the cubes or by placing several of them in a mesh bag and gently swinging. Cubes must feel light yet moist. This moisture ratio should be maintained until a plant germinates and its roots crowd the cube. The cube’s hole can be widened using a variety of ‘dibbers’, make sure whatever you use is clean and sharp (toothpick, nail, pen etc).

Rapid-RooterPeat-based plugs and polyethylene-based “rooter” cubes (Rapid Rooter / Sure to Grow cubes) – Suitable for soil, soilless, and hydroponic culture, they each retain quite a bit of water. The peat-based plugs and Sure to Grow cubes should be presoaked and their excess water gently squeezed out until the plugs are moist, but not soaking wet. Their holes can be widened with some light scissor work.

peat-pelletsPeat/coir pellets (Jiffy pellets) – These are compressed disks of peat or coir that expand when soaked in water. Encased in a net sheath, each disk expands to form a small cylindrical plug in which a seed can be planted. After presoaking, a plug should be lightly squeezed until water ceases to run out. The peat or coir in a plug is loose, so it’s possible to make a hole, plant a seed and fill the hole back in. These are great for soil or coco growers, are very easy to use and ‘beginner friendly’.

oasis-cubesSteady Gro and Oasis cubes – These two substrates are similar in structure: spongy and brittle. Oasis, however, are usually preferred for plants that will be grown in soil later. Both must be presoaked lightly, as shaking off the excess water will result in the inevitable breaking of the whole sheet, so treat gently and be light on the watering. “Light yet moist” is the key.

perlite_soiless_mixSoilless mixes (perlite / peat and perlite / vermiculite) – These mixes, typically at a 50-50 ratio, are excellent for germinating seeds and raising seedlings, because they are porous, retain water, provide good root zone aeration, and are inert. Watch the pH of peat-based soilless mixes, though, for they can sometimes be too acidic.

paper_towel_crop_out_brocolPaper towel – I like this method because it enables me to germinate the seeds first and then transfer them onto any of the starter grow media previously mentioned. It prevents having to throw away a cube in which a dud seed rotted (thus contaminating the cube and rendering it useless for propagation). When seeds are germinated in paper towel, their progress can be checked with minimal disturbance and either sterile or selectively-inoculated conditions can be maintained with ease. Paper towel is, by design, quite absorbent. Make sure excess water is drained before germinating your seeds.

Handling seeds

Seeds should be stored in a cool, dry area, preferably in a sealed environment. Many growers prefer to either refrigerate or freeze their seeds in order to preserve them until they decide to use them. Once you decide to germinate plants from seed, make sure the seeds are viable by inspecting them individually. Check for dried up, cracked, discolored, diseased or deformed seeds and discard them. If your seed packet looks moldy, discard it!

Presoaking

Many seeds have such a hard outer shell that they may benefit from presoaking in either plain, filtered water or a mild solution containing humates, B-1 vitamin, or kelp (which is rich in naturally-occurring growth hormones). Seed starting formulations or additives containing these three basic ingredients are easy to find in your local grow store and can be used to make a presoak solution. Soaking times vary depending on the thickness of a pericarp, or outer shell, and may last from a few minutes to a few days. Over-soaking can lead to macerated and rotted seeds. An alternative to presoaking the individual seeds is to simply add the seed-starting additive to the water used to soak the medium where the seeds will germinate.

Scarifying

Some seeds need to undergo scarifying. This can be achieved by two methods, depending on the plant’s habit: erosion of the pericarp or refrigeration. Erosion simulates the passing of a seed through an animal’s gut, where the digestive enzymes soften a pericarp enough for a seed to be able to germinate. Refrigerating seeds for a specific period of time simulates winter, which in many species is necessary for the seed to germinate. Check the Internet—most land-grant universities offer websites full of detailed information on the grow habits and proper cultivation techniques of almost every plant you can imagine. With a little digging, you will be able to determine which varieties benefit from which scarifying method.

Planting depth

Plant your seeds as deep as the seed is long. For example, if your seeds are 5 mm long, plant them 5 mm deep. When germinating in cubes or plugs, make sure that the hole is of adequate depth. A dibber can be used to make planting holes in loose or soilless substrate.

Orientation

Some seeds need to be planted upright because the taproot emerges from the bottom of the seed; others need to be planted sideways because the radicle (emerging tap root) tends to do a twist and a turn before it begins to grow in a downward habit. When planting larger, flat seeds like pumpkin and squash, it’s best to plant them on their thin side rather than flat side down. This helps to avoid water or wet growing media collecting on the seed surface. When in doubt, I plant my seeds on their narrow side at a 45⁰ angle. Works like a charm.

Lighting

Most seeds require no light to germinate. A plant’s light intensity requirements at this early stage are not that high, so putting a high intensity discharge (HID) lamp over your newly sprouted newborns is not a good idea. T-5 fluorescent lamps are excellent for seed propagation; one or two per seedling tray should suffice. LED lights are still in their infancy, so I cannot comment or recommend their suitability for propagation. Always wait until the plants pass the seedling stage and begin true vegetative growth before placing them under HIDs.

Nutrition

Seedlings require no food! Nature has invested them with cotyledons (baby leaves) rich in carbohydrates, hormones, and amino acids. It’s good practice to refrain from adding nutrients to your seedlings’ water until at least the appearance of the first set of true leaves. Once a first leaf pair begins to grow, a plant enters the seedling stage. As the weeks go by, increase your nutrient concentration gradually, starting with one fourth (¼) the recommended strength at the beginning of the seedling stage, not going beyond 375 ppm (0.5 NaCl scale), and using good filtered water. Increase the concentration by an additional ¼ every 2–4 weeks, depending on the length of your plant’s vegetative period. In indoor gardening we tend to do things rather quickly, so a ¼ increase in nutrient strength every 2 weeks will provide most indoor growers with an acceptable vegetative time frame, which will produce plants that are mature enough for reproduction, but compact enough to manage indoors.

Beneficial biology

Many people are recommending the introduction of a broad range of beneficial microbes into their propagation substrates. Some even recommend sprinkling seeds and clone tips in powdered inoculants or soaking them in microbial teas. My personal experience with this practice has been mixed, with some failures in seed germination and cloning. Then it dawned on me that I was introducing too many of these organisms, with their broad spectrum of activity, too early in the game. The seedling stage is not the time to put plants into overdrive—they simply are too young. Compost Tea’s and other microbial inoculants may be used during germination, but there are so many products on the market, that you have to be sure to use a high-quality, effective one that has been prepared correctly.  Tea extracts used for propagation should be substantially diluted and applied only once before transplantation. Wait until your plants have established root zones in the late stages of propagation, or in the early vegetative stages, before bombarding a substrate with beneficial biology. There are some specific microbial products that can help with seedling germination and propagation; just be aware that it’s not black and white when it comes to beneficial biology and propagation.

Temperature

Every seed species has an optimal temperature range for germination. Land-Grant university websites are a good source for information regarding your seed’s optimal germination temperature range. A seedling tray heat mat and a thermostat will ensure that your seedlings bask in the warmth of mild, bottom heat. Ensuring even temperatures increases homogenous germination and can help prevent root borne diseases. It also maintains optimal metabolism and enzymatic function at the root zone, which promotes overall plant growth.

Moisture

What is the easiest way to kill a seedling? By overwatering it! Excess moisture in the root zone accounts for most seed and seedling failures. An easy way to determine if your seedlings need watering is to fill a planter of the same size as your seedlings’ with the same mixture of substrate. Irrigate and shake off excess water. Compare the weight of the “control” container with your seedlings’. If your seedling container feels less than half the weight of the control planter, you should irrigate. If you want to get technical, you could use a scale to weigh your planters and irrigate once you notice that the seedlings’ planter weighs 75% less than the control planter. It’s better than sticking your finger and disturbing newly-formed anchor roots. This method can also be used with seedlings grown in cubes and plugs.

Relative humidity and propagators

Seedlings need a high relative humidity in order to thrive. Cold drafts, in particular, can shock or even kill days-old seedlings surprisingly quickly. However, too much humidity may aid the growth of opportunistic pathogens that can destroy your younglings even before they peek out of their shell. Covering your seedling tray with a propagating dome is a good way to prevent abrupt changes in temperature and humidity. Once seeds have germinated and established, the dome can be raised or vented, gradually over a few days. This will get the seedlings acclimatized to drier air; it’s a process known as ‘hardening-off’, which prepares them for the vegetative growth stage.

Do-it-yourself mini propagator

Put one or a few seeded planters (or cubes) in a zip-top, clear plastic bag. Make sure the bag is large enough to allow some room for air. Do not vacuum-seal it; rather, have it hold some air before closing and put it in your propagation area under fluorescent lights. Check the bag daily and tap-off any excess moisture that may form inside the bag. Once the seeds begin to germinate, begin opening the bag gradually as explained previously.

From seedling to early vegetative

Defining the line between the seedling and vegetative stage is a bone of contention among growers. Let us simplify things: observe your seedlings. A few clues will tell you when your plant is ready. Many plant species begin their vegetative period once the first set of true leaves is fully developed and a second node begins to open. The stem’s girth and rigidity will also increase. Yet the definitive sign of entering the vegetative stage is the aging of the cotyledons (or “baby leaves”). Once a plant has used up the food packets contained in the cotyledons, it is ready to feed from outside sources. The seedling has then grown to a young vegetative plant, and it is ready for you to initiate a nutrient feeding program until the root mass is large enough to transplant into soil or a soilless mix.

Step-by-step seed germination using the paper towel method

  1. Gather your materials. You will need: a plastic tray with lid (I’m using a Chinese takeout container), paper towel, seeds, & water.
  2. Soak your seeds.
  3. Fold paper towel pieces and place in the plastic tray. Moisten the paper towel with water. Do not overwater the paper towel! Use a fine-mist nozzle spray bottle, if possible, to thoroughly moisten all sides of the paper towel sheets. Drain off excess water.
  4. Gently place the pre-soaked seeds onto the paper towel. Try not to touch the paper towel, so it stays supple & well-saturated. Make inventory of the kinds of seeds you used, note their location on the sheets, & the date you began germinating them. This will save you a lot of headaches trying to identify which is what & will enable you to track how many days your seeds have been germinating.
  5. Gently cover the paper towel. Notice that some seeds may germinate better placed on the paper, uncovered.
  6. Cover your tray with an airtight lid, as moisture retention is crucial for proper germination. Place your tray under a gentle heat source. Wait for seeds to germinate.
  7. Check your seedlings daily, but only once a day: you want to maintain the seed environment as clean as possible, so always wash your hands before opening the lid. Keep in mind that seed germination times vary according to plant species.
  8. When the first root (usually called the “taproot” or radicle) begins to emerge from the seed, it is time to transplant the seedling into its starter environment. If the radicle has stuck or pierced through the paper towel, carefully cut the paper around it with clean, sharp scissors, taking great care not to cut the radicle. Transplant to your starting medium; the paper towel will degrade.
  9. Lay out your rooted seedlings under a light source of moderate intensity, such as tubular or compact fluorescent lamps. Try using a nursery tray with an air-pruning, raised wire screen. Ensuring good air circulation helps prevent root rot & enhances rooting.

steps

Words: Eliab Lozada


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