Fertilising Cannabis - Foliar Feeding, Fertigating & Manures

Nutrient Fertilisers create Healthy Roots and Healthy Cannabis

Almost no soil is naturally rich, while fertilizers, manures, and potent composts mainly improve the topsoil. But the water-wise gardener must get nutrition down deep, where the soil stays damp through the summer. Below are some old school gardening techniques that served their purpose well long before modern techniques took over.

GROW prefer the natural approaches and strongly suggest only using natural organic farming techniques to grow the cannabis safest for consumption. Also growing indoors using organic soil will prolong the effects of being high and make for a far more balanced effect, same as outdoor grown by the sun. That said if you are growing hydroponically indoors you may still benefit from an organic approach for fertilising your cannabis crops.

If plants with enough remaining elbow room stop growing in summer and begin to appear gnarly, it is just as likely due to lack of nutrition as lack of water. Several things can be done to limit or prevent midsummer stunting. First, before sowing or transplanting heavy feeders like cannabis, dig out a small pit about 40cm deep and below that blend in a handful or two of organic fertilizer. Then fill the hole back in. This double-digging process places concentrated fertility mixed 40-50cm below the seeds or seedlings.

Foliar Feeding Cannabis

Foliar feeding cannabis is another water-wise technique that keeps plants growing through the summer. Soluble nutrients sprayed on plant leaves are rapidly taken into the vascular system. Unfortunately, dilute nutrient solutions that won't burn leaves only provoke a strong growth response for 3 to 5 days. Optimally, foliar nutrition must be applied weekly or even more frequently. To efficiently spray a garden larger than a few hundred square feet, I suggest buying an industrial-grade, 3-gallon backpack sprayer with a side-handle pump. Approximate cost as of this writing was $80. The store that sells it (probably a farm supply store) will also support you with a complete assortment of inexpensive nozzles that can vary the rate of emission and the spray pattern. High-quality equipment like this outlasts many, many cheaper and smaller sprayers designed for the consumer market, and replacement parts are also available. Keep in mind that consumer merchandise is designed to be consumed; stuff made for farming is built to last.

Increasing Soil Fertility Saves Water

Does crop growth equal water use? Most people would say this statement seems likely to be true.

Actually, faster-growing crops use much less soil moisture than slower-growing ones. As early as 1882 it was determined that less water is required to produce a pound of plant material when soil is fertilized than when it is not fertilized. One experiment required 1,100 pounds of water to grow 1 pound of dry matter on infertile soil, but only 575 pounds of water to produce a pound of dry matter on rich land. Perhaps the single most important thing a water-wise gardener can do is to increase the fertility of the soil, especially the subsoil.

Poor plant nutrition increases the water cost of every pound of dry matter produced.

In terms of nutrient balance for outdoor crops, the best foliar sprays are organic. Any combination of fish emulsion and seaweed or liquid kelp is best. The most useful possible organic foliar is 1/2 to 1 tablespoon each of fish emulsion and liquid seaweed concentrate per gallon of water.


Foliar spraying and fertigation are two occasions when I am comfortable supplementing my organic fertilizers with water-soluble chemical fertilizers. The best and most expensive brand is Rapid-Gro. Less costly concoctions such as Peters 20-20-20 or the other "Grows," don't provide as complete trace mineral support or use as many sources of nutrition. One thing fertilizer makers find expensive to accomplish is concocting a mixture of soluble nutrients that also contains calcium, a vital plant food. If you dissolve calcium nitrate into a solution containing other soluble plant nutrients, many of them will precipitate out because few calcium compounds are soluble. Even Rapid-Gro doesn't attempt to supply calcium. Recently I've discovered better-quality hydroponic nutrient solutions that do use chemicals that provide soluble calcium. These also make excellent foliar sprays. Brands of hydroponic nutrient solutions seem to appear and vanish rapidly. I've had great luck with Dyna-Gro 7-9-5. All these chemicals are mixed at about 1 tablespoon per gallon.

Fertigation every two to four weeks is the best technique for maximizing yield while minimizing water use. I usually make my first fertigation late in June and continue periodically through early September. I use six or seven plastic 5-gallon "drip system" buckets, (see below) set one by each plant, and fill them all with a hose each time I work in the garden. Doing 12 or 14 plants each time I'm in the garden, it takes no special effort to rotate through them all more or less every three weeks.

To make a drip bucket, drill a 3/16-inch hole through the side of a 4-to-6-gallon plastic bucket about 1/4-inch up from the bottom, or in the bottom at the edge. The empty bucket is placed so that the fertilized water drains out close to the stem of a plant. It is then filled with liquid fertilizer solution. It takes 5 to 10 minutes for 5 gallons to pass through a small opening, and because of the slow flow rate, water penetrates deeply into the subsoil without wetting much of the surface. Each fertigation makes the plant grow very rapidly for two to three weeks, more I suspect as a result of improved nutrition than from added moisture. Exactly how and when to fertigate each species is explained in Chapter 5.

Organic gardeners may fertigate with combinations of fish emulsion and seaweed at the same dilution used for foliar spraying, or with compost/manure tea. Determining the correct strength to make compost tea is a matter of trial and error. I usually rely on weak Rapid-Gro mixed at half the recommended dilution. The strength of the fertilizer you need depends on how much and deeply you placed nutrition in the subsoil.

Worm Castings and Manures

One of the best fertilisers of the soil is made by saturating charred wood with urine. This may be drilled in with seeds in a dry state. For old gardens liquid manure is preferable to stable manure, and if lime or chalk be added it will keep in good heart for years without becoming too rich. A good manure is made by mixing 64 bushels of lime with 2 cwts. of salt. This is sufficient for one acre. It should be forked in directly it is put upon the ground.

Superphosphate of lime mixed with a small amount of nitrate of soda and forked into the ground is also a fine manure, but is more expensive than that made from lime and salt. Charred cow-dung is ready for immediate use. For established fruit-trees use, in showery weather, equal quantities of muriate of potash and nitrate of soda, scattering 1 oz. to the square yard round the roots. Peruvian guano, in the proportion of 1 oz. to each gallon of water, is a very powerful and rapid fertiliser. In whatever form manure is given, whether in a dry or liquid form, care must be taken not to administer it in excessive quantities, for too strong a stimulant is as injurious as none at all.

In ordinary cases loam with a fourth part leaf-mould is strong enough for potting purposes; and no liquid except plain water should be given until the plants have been established some time. For roses, rhubarb, and plants that have occupied the same ground for a considerable time, mix 1 lb. of superphosphate of lime with ˝ lb. of guano and 20 gallons of water, and pour 2 or 3 gallons round each root every third day while the plants are in vigorous growth. Herbaceous plants are better without manure. Liquid manure should be of the same colour as light ale.

Why AB Nutrients are better than a 1-for-all

This is a very simple one. When you use a 2 part nutrient solution, you will be able to achieve a wider spectrum of vital elements your product's needs. 1 part nutrients cannot achieve this because then then they will "self-react”. ALWAYS use a 2 part nutrient solution.

This is a section from our vegetation phase of the grow guide. Please also see our glossary of cannabis terms used in Australia.