Soil for your sensi
The best quality bud will always be produced organically in soil. Hydroponic systems with synthetic nutrient formulas may produce better yields, but they will never touch the quality of the best soil-grown organic pot.
Aside from the quality issue, there are many reasons to choose soil over hydro. Soil gardens pollute much less than hydro ones due to the method of fertilizer application ? there's no reservoirs to dump down the drain or heavy leachate from rockwool slabs running off into the environment. Plants grown in soil tend not to produce as much odor while growing as a hydro plant, due to the plants transpiring less. This, along with the fact that there are usually no irrigation timers to malfunction, have given many a grower a better night's sleep. How many days can an aeroponic unit keep your plants alive without power?
What is soilless mix?
When we talk about soilless mix, we are generally talking about a peat moss based substrate with additives that vary between brands and mixes. The most popular North American brands like Sunshine Mix and Pro Mix usually have sphagnum peat moss as the body of the mix, chosen for its water holding abilities, relatively inexpensive cost and high "cation exchange capacity" ? ability to hold nutrients for plant uptake.
Lime is added in two forms to raise the acidic pH of peat moss and supply a base of calcium and magnesium to the crop. Hydrated lime is usually added in very small amounts to provide long-term pH adjustment.
Perlite is added in varying sizes and quantities to make for a more porous mix. Wetting agents are used to help break the surface tension of the water and wet the mix more evenly upon irrigation. A starter charge of fertilizer is usually added to an EC of about 1.5 to provide enough nutrition for the first few days of growth.
Some brands offer mixes meeting organic standards with the main difference being the use of an organic wetting agent and a small amount of natural source fertilizer.
When buying soilless mix, it is best to stick to the big names like Premier, Berger and SunGro. There are a lot of garbage soilless mixes out there, and many vastly different qualities of peat on the market. Even among the big companies, the grade of mix that is sold in many retail garden center chains is not the same as what is sold to commercial greenhouses or nurseries.
The best quality peat moss comes in long strands, which translate into more air spaces in the root zone. One of the best byproducts of making top quality peat mixes is an abundance of peat dust and very small peat fibers. This is what soilless mixes sold in garden centers are made with. The problem with this is that the small fibers compact too heavily and do not let as much air into the root zone as a higher grade would.
The best bet is to buy the large 3.8 cubic feet compressed bales of soilless mix, as these are the ones that are usually top grade.
3 types of water
Regardless of whether you use drippers, water wands, or just a plain old watering can, understanding the properties of peat moss will make you a better gardener.
There are essentially three types of water that can be present in a soilless medium: unavailable water, available water, and free water. Unavailable water is water that is present in the medium, yet unavailable to the plant's roots because it is held tightly to the peat. Peat needs to be hydrated to a certain point before it has excess water that can be taken up by the plant.
Available water is that which is present over and above this amount.
Free water is water that fills the pore spaces in the soil, displacing oxygen. This type of water is something that should be minimized wherever possible, as this is what can damage roots, causing Pythium and other root diseases. The only time that free water has a place in pot growing is during the first few days of seed germination until radical (root tip) emergence, or when some amount of leaching is required. Even during leaching this should be minimized by using the methods described below.
Peat has a waxy coating that actually repels water; this effect is magnified when the peat is dry as a tighter waxy layer is formed. This is why if you water a very dry pot most of the water will run down the sides and out the drainage holes without wetting the medium.
Both to limit the amount of free water in the medium and to work around peat's water repelling abilities; staggered watering techniques works well. By applying the desired amount of water spread out over two or three waterings at 20-30 minute intervals you accomplish two things: First of all the surface tension of the peat is lessened after the first application so that the peat can more readily absorb the applied water. Secondly, free water in pore spaces has time to disperse through the medium or out drain holes, which minimizes the displacement of oxygen in the root zone.
When purchasing drippers, the best type are ones that are pressure regulated, which means that a specific pressure of water must be on the emitter before it will open. This eliminates the common occurrence of plants closest to the reservoir receiving more water than the ones at the end of the line. Nefatim is a common trade name for this type of dripper although several other companies manufacture them.
Staggered irrigation cycles are especially important when using drippers, as all of the water has to disperse from a single source point.
Capillary matting, trough systems, flood benches and wick systems all allow pots to be watered from the bottom. This offers advantages in convenience, minimized soil compaction and less disease in some cases as the foliage remains dry. This method, however, is more suited to growing ornamental plants than cannabis. The main problem is that the fertilizer salts accumulate in the top inch or so of the medium rather than being flushed out the bottom of the pot as in conventional practices. Soil tests taken at the bottom, middle, and top portion of the pot can be substantially different. This technique is more suitable for professional flower growers with access to proper testing equipment and lab analysis than for the average hobby pot grower.
Capillary matting, however, can be used very successfully as a complement to top-fed systems, especially in "sea of green" applications. Using capillary matting in conjunction with drip or wand watering works to ensure the entire crop is evenly watered, as pots that are a little drier than the rest can absorb the balance of water from the mat. Whenever possible use the porous black plastic mats designed to cover capillary mats as they cut down on algae growth as well as insect populations.
There are two limiting factors to the marijuana plant's growth rate which need to be kept in mind when watering; and unfortunately the two work against each other. Adequate water is required for plant growth, yet having a wet medium limits the amount of oxygen in the root zone, which reduces growth rates. A good wet/dry watering cycle maximizes both of these factors.
By irrigating until there's a slight leach (or a heavier one if you have bad water), then letting the soil dry out before watering again, you are balancing both of these limiting factors. This is not to say that the wet/dry cycle cannot be deviated from ? slight water stress is a great tool in controlling internodal stretch during vegetative or early flower.
There are also times in certain grow situations when keeping the soil fairly wet to encourage internodal stretch may be advantageous. For example, if growing a tight-noded Indica Screen of Green style you may want to encourage longer internodes during late veg/early flower in order to fill the screen more efficiently.
Either keeping the soil too wet, or more commonly, allowing the soil to become too dry between waterings, will both have negative effects on yield during bud formation.
Synthetic vs organic
On of the best things about growing in soil is how conductive it is to using organic source nutrients. Certainly it is possible to use organics in a hydro setup, but many who have tried simply find it to be too much trouble.
The organic versus synthetic fertilizer argument has been covered many times before, both in marijuana as well as normal gardening and farming circles. Proponents for synthetics often use the argument that a plant cannot tell organically derived nutrients from their synthetically derived rivals. Although this is true, what they don't mention is that with both organic and synthetic fertilizers, you are exposing your plants to much more than what is shown on the label.
The main downfall of synthetics is in the heavy metal contaminants like cadmium, lead, arsenic, zinc, which are often present in the formulation. Cadmium and arsenic for instance have been shown to cause cancer as well as other problems. Levels of these contaminants vary considerably between fertilizer brands and are also present in some amounts in organically based formulations.
Synthetic proponents often argue that organic fertilizers come from unknown sources which may contain many of the aforementioned contaminants. Proof is in the pudding, however, and recently the state of Washington has required all fertilizer companies to show the pudding. Take a look at their website and do the detective work yourselves. Most of the popular brands used by marijuana growers are listed along with their respective heavy metal contents.
By and large the organic fertilizers provided extremely clean sources of nutrients according to this database. It would seem that marijuana would be more likely than many plants to cause ill effects on humans from heavy metal contaminants, both because of its efficiency at accumulating them and because the product is often inhaled directly into the lungs. Cannabis is well known for its above ordinary ability to accumulate heavy metals as it has been used on many occasions to clean up contaminated soils. To my knowledge, no studies have been done on where these heavy metals accumulate within the plant.
Organic fertilizers can be applied to soilless mixes in liquid form, by pre-mixed powdered slow release nutrients, or a combination of both. Most of the liquid mixes that have been around
for a while, such as Earth Juice, Pure Blend and others, are safe bets.
Fish emulsion formulas work well and are inexpensive, although they likely should not be used exclusively. Out of the organic source fertilizers commonly used to grow weed this is probably the highest in heavy metal contaminants, as fish are well known to accumulate mercury and other metals. Some growers also claim that it affects the taste of bud when used in flower.
All-Mix or "Super Soil" recipes abound among growers and on the Internet. Some are good and some are not, so do your research and you should be able to find a good one. Some hydro shops also sell pre-mixed products for this purpose.
There are many synthetic fertilizers available on the market, many of which are tailored to meet the needs of marijuana (although this is likely not mentioned on the label!). Stick to the popular brands or ones that are popular in your area.
Large-scale growers who wish to be able to tailor nutritional needs more carefully to the strain and growth stage may wish to try using bulk greenhouse grade fertilizers. These come in bags such as 10-52-10, 14-0-14, 20-10-20, or can be custom made from raw salts such as calcium nitrate and monopotassium phosphate. These items can be obtained inexpensively and without hassle from your local agricultural suppliers, but they usually come in 15 kg bags minimum.
Fertilizers similar to these are usually available in your local nursery as "all purpose" fertilizers. All of these can be used successfully to grow marijuana, but must be used in conjunction with calcium and magnesium based fertilizer like 14-0-14, which is usually only available from agricultural suppliers in the large bags.
These types of "all purpose" labeled fertilizers common in garden centers contain little if any calcium or magnesium. This is not an issue for people growing houseplants, as the lime in the soil provides sufficient quantities. However, for fast growing plants like marijuana, calcium and magnesium based formulas must be used in conjunction.
The cal/mag formula can be either mixed with the other fertilizer in appropriate amounts in the reservoir, or applied on an alternating watering schedule. For instance, during the veg stage, water once a day with 20-10-20, then the next day with 14-0-14. Or flower one time with 10-52-10, and one time with 14-0-14. The frequency of the 14-0-14 applications can be staggered depending on crop stage or desired fertilizer ratio. It does not have to be on a 1:1 ratio.
Newer growers would do best to stick to tried and proven pre-made formulas (General Hydroponics, etc.) from your local hydroponics store if growing with synthetic nutrients. Many of the organic formulas described above are also very beginner friendly.
When soilless mix suppliers prepare their mixes they are not gearing them to any specific plant and certainly not the needs of cannabis. The pH and porosity is designed to provide adequate conditions for a wide variety of plants. Some plants like a low pH, some like a high pH, some like a wetter root environment, and some like it drier. Most soilless mix takes a middle ground on these issues.
All of these factors can be easily adjusted to better suit the needs of cannabis. Extra dolomite lime can be added to raise the pH from the usual pre-adjusted 5.8 into a more acceptable 6-7 range (6.5-7 seems to work best for organic nutrients). Additional perlite will increase the drainage and amount of air space in the medium more to Mary Jane's liking.
Cannabis grows best in soil at a pH between 6 and 7 and an EC of 1 to a low 2, depending on the strain. The absolute lowest you should ever let your pH drop to is 5.8, as below that toxicity problems are likely and accumulation of heavy metals in the bud become more probable.
Both pH and EC in the soil can change drastically depending on the water source, nutrients, and other factors. High phosphorous synthetic "Bloom Boosters" can easily make soil pH drop drastically especially if using cheaper grade fertilizers, which do not have "pH stabilizers" included in the formula.
Many veg formulas with large amounts of urea or ammonium nitrate in the formula can also cause rapid pH decline. Water or fertilizers containing high amounts of calcium or potassium generally increase the pH of the medium over time. Most of the higher end hydroponics fertilizers on the market are well balanced and adjusted to help avoid wide pH swings.
Always remember that in soil the pH or EC or the irrigation water is not as important as the actual pH or EC of the medium. Medium conditions can be measured by catching leachate for testing, using high quality soil probe meters, or mixing a soil sample with distilled water before measuring. Leachate tests can be considered fairly accurate at determining the actual pH and EC, provided it is not a heavy leach, which may alter the readings. About 5% leaching is about right for this.
Soil probe meters are available for both pH and EC, although they are a fair bit more expensive than a normal meter. These probes will give the most accurate reading, but the cheap versions are no good (anything under $100 is suspect).
As distilled water has an EC of 0 and almost no buffer capacity, mixing a soil sample at a water to soil ratio of 2:1 will provide an accurate yet diluted EC measurement and a very accurate pH indication. Let the mixture sit for twenty minutes then take a measurement using standard meters or test strips. The pH can be taken as is, but the EC must be multiplied by 2.4 to take into account the pore space and dilution factor.
Soil temperature is just as important in soil growing as solution temperature is in hydro growing. Many garden supply stores sell soil or compost probe thermometers, which are inexpensive ($30-40.00) and well suited to this application. They can be left permanently imbedded in the medium or used as needed. Keep in mind that they take a few minutes to display the correct temperature after being inserted.
Proper soil temperature should be constantly maintained at around 70?F (21?C). Allowing soil to sit cold even for the first couple of hours before the lights warm up the pots can cost you in yield, as it makes it harder for the roots to uptake phosphorous. Usually just keeping the plants up off cold concrete floors or insulating them with foam panels is sufficient to keep temperatures warm enough.
In colder rooms with no night cycle heating it may be necessary to use a bottom heat source. An easy method to create bottom heat is to fill a shallow tray with moist sand and run heat cables through the sand. The pots can be placed directly onto the sand or on a plastic covering.
One downfall to growing in soilless mix is that bugs and their eggs may enter your grow room with the soil. It does, after all, originate in a peat bog somewhere. Although some people claim that spider mites were brought in with their soil, this is the exception rather than the rule. Fungus gnats, however, do occur with some amount of regularity.
Most batches of soil will be free of these pests, and even when they are present they are quite easy to deal with. Mixing diatomaceous earth into the top half-inch of soil in the pot gives good control. Drenching the medium with organic pesticides such as bacillus thuringiensis variety israelensis (common trade names are Gnatrol or Vectobac), neem oil or SM90 also gives excellent control.
Fungus gnats can spread diseases and viruses and certainly are not a tasty addition to a nice cone of kind bud. Keep an extra careful eye out for these critters when rooting cuttings directly in soil as the larvae can burrow into the wounded base and cause serious damage or death to the cutting.
Pot size and color
Pot size will be determined both by your strain and growing cycle. Sea of green growers usually use anything between one and three gallon pots, while bush growers use pots up to about 10 gallons. Ideally, your plant should be just slightly pot-bound by the time they are going into heavy bloom. It is not clear why this is, but it seems to give a slightly fuller bloom. Anything more than this is a waste of soil.
Transplanting should be done when a firm root ball has been formed and smaller feeder roots have filled out to the sides of the pot. Using several container sizes before the final one provides a much denser root ball, which in turn provides better buds. Roots tend to shoot straight out for the sides of the container and then circle it, leaving much of the area in between relatively void of roots. For example, by transplanting a clone in a 4" pot to a 6" one gallon pot before its final 8" three gallon pot, you will achieve a much denser root ball than if the 4" pot was transplanted directly into the 8" container.
Square pots are always better than round as they hold more soil in the same square area of space. Many growers debate whether white pots or black pots are better, but for the average indoor grower color likely makes little difference.
Black ones will get hotter (not always a good thing) and block light from reaching the roots, while white ones stay cooler yet may let some light into the outer perimeter of the root zone.
Clone growers may prefer to grow in large bed-type systems where many plants are planted in the same tub. This allows more room for root growth and avoids the circling problem associated with pots.
Peat moss is not a renewable resource. As I like to think that a good portion of marijuana growers are environmentally conscious, it is in everyone's best interest for growers to take a good look at some alternatives.
Coconut coir is a good substitute that many growers have been experimenting with or switching to altogether. A byproduct of the coconut industry, coir is a sound alternative to peat. The main problem experienced by growers so far is that coir can have higher levels of sodium than ideal when harvested from coastal areas. Any good grade of horticultural coir should be low sodium.
Some non-cannabis growers have also experienced problems in rooting cuttings of some types of plants, presumably from some type of hormone present.
Yet aside from its environmental aspects, coir has a much better starting pH than peat (6-7) and is more porous. As with anything new in growing, don't jump right in until you have done some trials to make sure it will work properly with your given conditions and techniques.
Growing pot organically in soil is one of the finest examples of the benefits of keeping things simple. The world would be a better place if more people rolled up their sleeves and dug around in the dirt.
? Washington State fertilizer database: www.cannabisculture.com/news/fert