While planting rooted cuttings is a common way to propagate cannabis plants, the time honored tradition of starting with seeds is still the choice of many. Advantages to starting Cannabis plants from seeds include having a taproot, possibility of male plants for making more seeds, variety, ease of transport, and storage.
Proving
Cannabis seeds contain tiny dehydrated plants that await conditions (warmth and moisture) conducive to sprouting. Close examination of the pointed end of a cannabis seed will show that it does not come to a perfect point. There is a small opening at the tip called a micropyle. This allows for moisture to enter the interior of the seed, causing the dehydrated plant inside to swell, bursting through the seed coat at sprouting. The root tip will emerge from the micropyle and use hydraulic pressure to separate the two halves of the seed coat. To facilitate this process, the seeds may be soaked in water for several hours before proving or planting.
Seeds can be proved before they are planted. This is commonly done by sprouting seeds in a moistened paper towel to prove they are viable and capable of sending out a root.
To prove a seed: Moisten a paper towel, wring it out, flatten, and fold around seeds. Place in a labeled plastic bag and set in a warm location. Moist cannabis seeds germinate best at temperatures between 68 and 86 Fahrenheit, with 75 F being near ideal. In cold settings, a heating pad may be used to raise the temperature of seed trays, but care must be taken that they do not get too hot. Change the paper towel every few days to keep it fresh if needed, and carefully plant the sprouted seed once the seed coat cracks and the radicle (first root) emerges.
Sowing
Seeds also can be sprouted by simply burying them 3 to 4 times their width, and keeping them warm and moist, but not soggy, until sprouting. To prevent the media from drying out too quickly, sometimes domes or plastic sheets are used to keep the humidity high while seeds sprout.
Sprouts
Once sprouted, the tiny plant is no longer in stasis. A properly stored seed can remain viable for years, but once sprouted the plant begins to need warmth, moisture, and air. In fact, it becomes dependent on them and will expire if denied them for extended periods. Once seeds have started to sprout, they must either grow or perish. The radicle spreads underground to become the root system. The seedling leaves will unfurl, the seed coat will drop off, and the shoot apical meristem (growth tip) will develop the first “true” leaves and begin normal growth. Seedlings are tender and susceptible to mortal damage, and as such should be treated with a light hand and care.
Seedlings
Regardless of how they were initially sprouted, seedlings require closer care than adult plants. While an adult plant has an established root system, seedlings start with a single short root. If this root (particularly the tip) becomes damaged while planting, then the sprout may well perish. Likewise, as sprouts have small roots (and few liquid reserves), it can be easy for them to wilt and expire if the growing substrate becomes too dry. Seedlings are also more prone to damage from overfeeding, and from extremes in conditions.
Initially, the seedlings can feed off the nutrition stored in the pair of cotyledons (the rounded seed leaves), but as the nutritional stores are used up, they will begin to need nutrition gathered by the roots. Eventually the cotyledons will become used up, wither, and fall off, at which time they no longer contribute to the plant. If the growing media does not contain nutrients, then they should be supplied before this point is reached. It is common to start seedlings off with a feeding regimen that begins with a very mild concentration (a quarter or so of regular strength), which is increased as the plant develops into adolescence and adulthood. Feeding strength should be reduced (or temporarily eliminated) if there are any signs of nutrient burn. Any yellowing at the leaf tips should be closely monitored to determine if the cause is a lack of nutrition or due to overwatering.
Heat from intense lighting can also have a detrimental effect on seedlings, as they (and their containers) tend to have a smaller mass, and are therefore more susceptible to swings in conditions than larger established plants. For this reason, many gardeners start their sprouts under mild lighting. Seedlings not getting enough light will stretch and become lanky.
Shock
Plants have a defense mechanism to help them through temporary radical changes in their environment. The plant will slow or shut down and wait for conditions to improve. This is commonly referred to as “shock.” A shocked plant will hunker down and then wait a period of time (a couple weeks is common) to see if conditions improve. If the shock is intense enough, the plant can die while in this waiting period. An example of this is a seedling sprouted under mild conditions indoors, which is then transplanted into a harsher environment (either blazing sun or chilling cold). Other common causes of shock are extensive root damage or disturbance (transplant shock), or a sharp increase in nutrient strength.
Hardening Off
To avoid (or at least minimize) shock, plants can be gradually introduced into their new environment. The more radical the change, the longer and more important it is to harden them off. This is done by either moving the plants into the new environment for increasingly longer durations, or in a series of steps. To harden an indoor-started seedling that will be planted outdoors, place the plant outside during the nicest part of the day in a mild location and return it to shelter later. A common method is to put it in the new environment for an hour or two the first day, increasing the time spent in the new environment by an hour or two every day for a week or so until it is acclimated enough to remain outdoors full time. A plant going outdoors may spend longer lengths of time in the shade before moving to full sun conditions, or an indoor plant may start at the edge of the grow light’s range and gradually get closer to directly underneath. Any large change can trigger the reaction, so almost all such changes are easier for the plant to accept if done in a series of steps rather than abruptly. Cannabis can tolerate higher levels of nutrients when the solution is increased incrementally than it can if the levels are increased sharply.
Much like the youth of many living things, seedlings are more susceptible to certain types of injury than adults, and extra care should be taken to protect them. By avoiding conditions conducive to shock, plants can save time, grow healthier, and develop faster than those that lose weeks recovering from the condition.