Care of Seedlings
Successful seed germination requires optimal conditions including moisture, warmth and suitable grow media. Light is not necessary until the first leaves, or cotyledons, have emerged from the seed shell. Once seeds germinate, it is important to maintain substrate and environmental conditions for optimal seedling development.
Seeds can be started in a variety of growing mediums, including rock wool, peat moss cubes or loose potting soil mixes. If using a potting mix, be sure to use a seed starting or untreated blend to avoid any possible salt toxicity on young plants. Also, be sure to avoid using mixes that have large, chunky bark particles. This can cause the medium to dry too quickly and harm new root development. Seeds can be soaked or wrapped in a damp paper towel one day prior to planting to encourage faster germination.
Moisten growing medium of choice with filtered or distilled water, place seeds in medium, cover seeds slightly, and keep in a warm and dark area. Plain water or a light nutrient feed(200 ppm) can be used during this stage. Ideal ambient air temperatures are 75°-85°F, with 75-85% relative humidity. Soil temperatures should be 60°-70°F to encourage seed germination. If outdoor soil has not reached this temperature range, seeds should be started indoors. Ambient CO2 levels are ideal; no supplemental CO2 is required at this stage. If levels are higher, seedling development may suffer. Keep a close watch on seeds and provide low levels of light once germination occurs. As plant matures, increase the light intensity gradually. This can be provided with fluorescent T5, LED or metal halide bulbs.
Once roots develop and the first set of true leaves has formed, the young seedlings will need nutrients. Begin or continue the light nutrient feed at 200-250 ppm. For best results, continue to use distilled or reverse osmosis water for seedlings. Tap water with a pH over 7.0 or an EC over 0.4 (200 ppm) can be problematic for nutrient availability and root development. As more leaves develop, increase feed rate up to 400 ppm as needed, using a vegetative nutrient solution to provide the necessary nitrogen and other elements required for early plant growth.
Essential Nutrients for Growing Cannabis
All plants, including cannabis, require certain essential nutrients to grow healthy, strong, and productive. From essential macronutrients to secondary nutrients and micronutrients, find out how much you need of each.
Source: Maximum Yield, September 23, 2019
Cannabis has thousands of unique properties, but like any other plant, it requires the same essential nutrients to properly grow and produce the desired yield of buds. Plants need relatively large amounts of macronutrients, lesser amounts of secondary nutrients, and small to trace amounts of micronutrients to germinate, grow, flower, and produce seed. All told, there are about 20 essential nutrients needed for optimal cannabis growth and development.
A nutrient is considered essential when it meets certain criteria. It must be directly involved in plant nutrition, be a vital component to the plant’s life cycle such that without it the plant would die or not be able to perform one or more of its necessary functions, and it must be unique enough that no other nutrient can replace it or perform the same function. Let’s examine which nutrients found in nature are essential for the cultivation of top-shelf cannabis. These vital nutrients can also be found in organic fertilizers.
The group of nutrients needed in large quantities by plants is collectively known as macronutrients. Some of these are provided by the environment, while others are provided by or need to be added to the soil.
Provided by air and rain, Oxygen (O), hydrogen (H), and carbon (C) are sometimes excluded in discussions of essential nutrients. This is because they are not elements that are often lacking, despite being needed in large amounts. They are also not ones that are components of any fertilizer or commercially-available nutrient package.
The other macronutrients that are needed and can be added to soils or other media are nitrogen (N), phosphorus (P), and potassium (K). Most commercial formulations of dry or liquid fertilizers will have three numbers on their packaging. These three numbers refer to the percentage by volume of N, P and K. Each of these individual essential nutrients performs a different –but vital– function to cannabis plants.
What follows is an oversimplification of the exact roles of each nutrient (in some cases, we still don’t know what all essential nutrients do and how exactly they interact with one another). Nitrogen is needed for the development of foliage and the production of proteins. Phosphorus is critical for root, flower, and seed development. Potassium is a requirement of overall plant health and aids in water absorption.
Cannabis needs different amounts of essential macros depending on the stage of development. Nitrogen is needed in higher quantities during the vegetative and bud-forming stages than during the flowering stage.
For its part, phosphorous is needed more during the flowering stage and is only required at about half the ratio of N levels during the vegetative phase of development. During this phase, K is needed at between half and two- thirds the level of N.
Essential Secondary Nutrients
Some sources do not separate the secondary nutrients and instead lump them in with the macronutrients since they aren’t needed in the same high quantities as the macronutrients.
They do, however, need to be in a significantly higher quantity than the micronutrients, so they are separated here. The essential secondary nutrients are magnesium (Mg), calcium (Ca), and sulfur (S). These nutrients are often unavailable to cannabis if proper pH levels are not maintained (more on that later).
These secondary essential nutrients perform a wide range of critical functions to proper cannabis development. They are often necessary components or complementary parts to other nutrients and functions. They are all needed for plant and root growth, but they do have specific roles. Calcium assists in transporting other nutrients and aids in their absorption. Magnesium is a critical component of chlorophyll. Sulfur aids in the transport of chlorophyll, but also assists with plant metabolism and transpiration.
The lesser amount required to aid in the proper growth and development of healthy cannabis should not be mistaken as being less important than the micronutrients. The same can be said for the diminutive amounts of micronutrients needed.
The number of micronutrients listed as essential can vary based on the source. Like secondary nutrients, it is somewhat a matter of classification as some list the secondary nutrients as micronutrients. Either way, they represent minerals and elements that are not as abundantly available on Earth and as such are not needed in very high amounts by cannabis plants, but are still necessary.
No matter what source, boron (B), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe), and molybdenum (Mo) are always listed as essential micronutrients. Like the other essential nutrients, all micronutrients either have a unique function or serve to assist in the functions and processes of the other nutrients.
What follows is not an exhaustive list, but a sampling of some of the roles of micronutrients and how they aid in the development of cannabis plants:
- Boron — helps with the development and growth of root tips. It also helps plants to absorb Ca and transports sugars within the plant.
- Manganese — is a vital component of chlorophyll production and the photosynthesis process. It also aids with enzyme interactions.
- Zinc — aids in the development of stems, leaves, and branches. The more mature a plant is, typically the more Zn is present and required.
- Copper — aids in the development of plant proteins and helps with the strengthening of stems and branches.
- Iron — is important for chlorophyll production. Iron deficiencies often present themselves as a yellowing of the leaves between the leaf’s veins (nueinal chlorosis).
- Molybdenum — helps to process nitrogen.
Other trace minerals thought to be essential include cobalt (Co), silicon (Si), chlorine (Cl), and selenium (Se). Not all sources agree on their inclusion in the essential group, though they are important to support all plant life.
pH and Nutrient Availability
As important as nutrients –if not more so– is the pH of the soil or media the cannabis is growing in. The pH is a measure of the acidity or alkalinity of soil or growing medium.
Soils or other media with a pH of less than 7.0 are acidic; soils or other media with a pH greater than 7.0 are alkaline. The pH scale is exponential, with each number representing a factor of 10 times greater or less than the number next to it. For example, a pH of 6.0 is 10 times more acidic than a pH of 7.0, and 100 times more acidic than a pH of 8.0.
What does this have to do with the essential nutrients needed for growing cannabis? Nutrients may well be present in sufficient amounts to support robust growth and plant function, but they can be locked out or otherwise made unavailable to the plant. The ideal pH range to try to maintain for cannabis is generally accepted to be in the 6.0 to 6.5 range, with some variation depending on media selected. To determine pH, make sure to perform a soil analysis.
Soil testing can be a simple do-it-yourself procedure or can be done by a reputable lab. It’s a routine procedure and is relatively inexpensive either way. A soil testing DIY kit costs only a few dollars and involves sending a smart amount of soil or growing media to a private or university-owned lab. Within a few days to a week, you will receive a detailed report with your soil’s current nutrient levels, along with the percentage of organic matter, and other relevant information. Doing this test can help you make the necessary adjustments to ensure your cannabis as what it needs to thrive.
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Seed Germination: How to Give Your Seeds a Strong Start
Planting seeds ends in either the thrill of that first tiny green shoot or the disappointment of a failed germination. Here’s a few tips on how to make sure your plantings end in smiles, not tears.
Seeds are amazingly compact packages of stored genetic material that are conveniently portable, readily available, and, given the right conditions, an easy method of establishing a new hydroponic crop. However, a rapid and healthy germination process is vital to their success.
While indoor gardeners have the advantage of a carefully controlled environment—which vastly assists germination compared to the fluctuating environments and predators in outdoor fields—the germination process is still reliant on a few essential conditions, as it’s a sensitive stage of development that can be prone to problems.
A seed consists of an outer protective cover surrounding an embryo and its stored food supply. For a seed to germinate, it must meet three basic requirements: the embryo must be alive and viable, the seed must not be dormant, and the environmental conditions of moisture, oxygen, and the correct temperature must be present to trigger the process.
Most of the seeds we buy for common hydroponic crops do not have any biologically imposed dormancy; however, seed viability is an often-overlooked issue that can account for unexpected germination failures.
It’s not possible to visibly determine if a stored seed is viable and able to germinate; a live seed looks very much like a dead one and both will imbibe water when sown.
A seed lot that has lost some viability due to age or poor storage conditions may be slow and uneven to germinate, and the resulting seedlings may lack vigor and be deformed or prone to pathogen attack.
For this reason, only investing your time and effort into fully viable seeds prevents the disappointment of germination failures.
How well a seed lot germinates depends on the qualities of the seeds at harvest and how they were stored, both before and after sale to the grower.
Seeds are living and respiring tissue, and those that remain viable the longest tend to have the largest nutrient store and low moisture content.
The water content of most ripe seeds is around five to 20 per cent of fresh weight, compared to 80-85 per cent for most live plant tissue. Drier seeds remain viable for longer than those with more moisture.
Seed storage conditions—in particular, lower temperatures, slow respiration, and low humidity—aim to slow the rate of respiration and therefore increase shelf life of viable seed. Since seed respiration uses oxygen, decreasing the oxygen supply also increases seed longevity.
At the same time as slowing the rate of respiration, the embryo must be protected from conditions that may cause injury and reduce viability of the seed.
Seed producers and seed companies tend to store each species under the correct conditions and in suitable packaging—often made of moisture-proof material—marked with seed lot testing information.
Sourcing Your Seeds
Seeds obtained from reputable suppliers will also have an expiry date printed on the packaging. These seeds should remain viable until the expiry date or even for some time after if the seed packet remains sealed.
However, growers are often unsure how to best store open packets of seed. Seed hoarding, which is the inability to throw out expired seeds contained in open packets, is fairly common among gardeners and a frequent cause of germination issues or the production of overly weak seedlings.
Opened seed packets, which have been exposed to moisture in the air, can be resealed or placed into a plastic container with desiccant.
Also, both sealed and opened seed packets are best stored at temperatures of less than 50˚F, so for most vegetable and other common seeds, refrigeration is a good option.
Storage of seeds in warm conditions hastens respiration and speeds up the depletion of the nutrient stores within the seed tissue.
Ability of seed to maintain a high level of viability during storage is also somewhat species dependant. Tomato seeds stored for years are often capable of geminating with few problems, whereas pelleted lettuce seeds may only remain viable for a few months after the package has been opened.
For those species that have a limited shelf life, growers should only purchase the amount of seed required for immediate sowing, even if it means only buying in small quantities each season.
Of course, sometimes you miscalculate the amount of seed to buy. Considering that some hybrid seeds used for hydroponics can be expensive, throwing out expired packets can be somewhat challenging for thrifty growers.
Seed Viability Testing
Fortunately, it is possible to test the viability of a seed lot to determine if it is worth investing the time and effort into sowing.
Viability testing is carried out by placing a small sample of seeds on moist paper towels inside a plastic bag. These are then placed into a warm environment at the correct temperature for germination of the species being tested.
The seeds are checked daily and those that germinate—that is, the radicle (young root) emerges from the seed coat—are counted.
The test is complete when no further seeds germinate for three consecutive days; at this stage, the non-germinated seeds can be considered non-viable.
Then, the percentage of seed that germinated can then be calculated—the higher the percentage, the more viable the seed lot—and a decision can be made on whether it is worth sowing the rest of the seed.
The Germination Environment
Assuming a seed is fully viable, germination issues can arise due to problems with the environment. Incorrect temperature is one reason.
Each species has its own ideal temperature for germination. Some species, such as lettuce, prefer cooler germination temperatures and can fail to germinate if it is too warm (seed may enter a secondary dormancy if this occurs). Others such as tomato, cucumber, and capsicum require much warmer conditions.
Another common problem is overwatering, which eliminates vital oxygen, as many inexperienced growers tend to overestimate how much moisture is required for germination.
A good seed-raising substrate should be able to retain sufficient moisture while being free-draining so that plenty of oxygen is present. Many seeds benefit from not being watered while germinating, so a light plastic or paper covering to retain moisture is usually beneficial.
Above: Damping off caused by disease pathogens is much more common under saturated conditions.
Another often overlooked factor to consider when starting from seed is water quality. Many seeds and young seedlings are more sensitive to poor water quality, water treatment chemicals such as chlorine or chloramines, hard water, high pH, and other factors than hardier older, more mature plants.
Damage can easily occur, so serious propagators may want to consider investing in a small reverse osmosis unit to provide mineral-free water.
Small growers can use bottled or carbon-filtered water for the early stages of germination, while those using rain, dam, or well water would be best advised to boil or sterilize their water to eliminate the potential for soil-borne pathogens that can cause root rot and seedling disease.
Damping off is a term used to describe the death of small seedlings from attacks by certain fungi, primarily Pythium ultimum and Rhizoctonia solani, although other fungi, such as Botrytis and Phytophthora species, may also be involved. Insects such as fungus gnats can transmit Pythium and these other pathogens.
Conditions usually associated with damping off include contaminated water or media, overwatering, poor drainage, and a lack of ventilation.
To reduce the risk of attack, keep propagation areas clean, hygienic, and free of old plant debris that may be harboring spores with regular cleaning of all surfaces, trays, and equipment.
Other potential sources of pathogen spores are some organic growing mediums, such as composts and peat, and untreated water supplies. So, starting with a pathogen-free substrate and a clean, high-quality water supply can help prevent many of the problems associated with pathogens.
Also, seeds that have low viability produce weak seedlings, which are far more prone to attack by opportunist pathogens. In fact, any factor that weakens the plants or slows the germination process also predisposes the germinating seed to Pythium.
This includes low or high temperatures, lack of air movement, and excessive humidity as well as over saturation of the growing substrate.
High salinity or salt buildup around the developing seedling can also stress young plants and promote disease occurrence, so it’s best to use low-mineral water supplies during the germination process.
A low EC nutrient solution should only be applied once the first seedling leaves have expanded and the plant is able to take up minerals in the developing root zone.
Seed treatments are a technology worth taking advantage of both to increase the speed of germination and help prevent issues such as seed rot. Many small and difficult to handle seeds such as lettuce can be purchased in pelleted form. This “thermo pelleting” assists the seed to germinate in a wider range of temperature conditions.
Some seeds may be coated in fungicides to help control pre- and post-germination rot pathogens. Other seeds may be “primed” to promote rapid germination and most are viability tested before sale.
For soilless growers, the use of specialized propagation materials is a worthwhile investment. Most hydroponic gardeners raise seedlings in specially designed propagation mediums. These can be made of synthetic or organic materials, such as sterile foams, rock wool, coconut fiber, composts, and more.
Seeds play a vital role in plant production, allowing growers to reproduce the best genetics for uniform crop growth, high yields, and other desirable characteristics.
Seeds also allow plant varieties to be easily packaged and transported around the globe or to be stored for future use. These days, even small growers have access to high-quality, viable seeds for a wide range of cultivars.
Germination is a fairly straightforward process, but paying attention to moisture, oxygen, temperature, and seed viability, as well as maintaining a clean and well-designed propagation area all help ensure reliable results with every crop.