11 minute read
Living Organic Soil - Part 2
BY GARETH HOPCROFT AND BEN BLANDFORD,
A living soil mix is quite different from a standard potting soil, which is often just a blend of peat, perlite, and synthetic or organic base fertiliser designed to last only a few weeks. The ingredients for a standard potting soil are selected mostly based on cost and to allow a smooth production process without any real concern for the quality of inputs. Although a living soil may use peat and perlite as well, the critical ingredient is a high percentage of quality compost. When blended with natural organic inputs and minerals, the mix is allowed to ‘cook’, enabling microbial activity to bring everything to life. This process takes several weeks – not an easy feat for commercial production – and requires specialist knowledge, skill, and attention over this period.
Building the Basis of Living Soil
A quality living soil structure needs a right balance of water retention and air space, but also must be able to drain freely and dry evenly. There are three components to build a good soil structure: compost, aeration, and organic growing medium. Compost sources will either be from thermophilic compost or vermicompost. Thermophilic compost is made by mixing and building piles of green and brown plant material, and sometimes manures and other natural by-products as well. This helps to encourage biological activity from aerobic bacteria. The compost piles are regularly turned to avoid overheating caused by the feeding and reproduction of the microbial colonies and then, once stable, they mature, allowing a diverse range of microorganisms to develop.
Vermicompost uses similar ingredients but incorporates the action of worms to break down the organic material without any heat generation. High-quality vermicompost often uses finished thermophilic compost as a proportion of the inputs. The constituents of compost and how the process is managed are both essential as they form the engine that drives everything else. Compost is a powerhouse of nutrients and microbes and is the life source of your living soil mix.
Aeration is vital when building a new soil mix. Aeration additives provide small air spaces throughout the mix to allow root respiration and healthy microbial activity. A functional aeration additive will also add structure to the blend to avoid compaction over time. The most popular options are perlite, pumice or lava rock. Some growers also opt for crop by-products such as rice or buckwheat hulls.
Finally, we need an organic growing medium to enable both the roots to grow and microbial processes to occur. Sphagnum peat moss is the most popular choice with growers, but coco coir is also a good option. Peat, however, is acid and needs to be pH buffered with the addition of limestone, whereas coco coir doesn’t.
When building your living soil, an excellent ratio to start with is ⅓ compost, ⅓ aeration, and ⅓ peat or coco. Tweaks may be needed depending on the water-holding characteristics of your compost and aeration additive, and the grade of the peat or coco. You can always make a small mix and see how it feels and acts once in a pot. A good rule of thumb is to grab a slightly damp handful, squeeze it, and look for minimal runoff. It should also break apart again quickly when you release your grip. This will encourage strong root development to support vigorous, healthy plants.
Buckwheat hulls
Credit: Ben Blandford
Once the structure is complete, some additional inputs are required to help achieve a good nutritional balance. It’s essential to use amendments that break down at different speeds and contain a diverse range of nutrients. Some of the best ones are kelp (seaweed), crustacean and neem meal, rock dust, limestones, and gypsum. There are options such as fish meal, alfalfa, comfrey, nettle, and insect frass as well to boost the soil even further. Some growers turn to animal by-products to build their soil nutrients, such as blood meal, bone meal, hoof and horn for a quick and cheap fix, but it is important to check the sources of these materials as they will often come from non-organic GMO fed livestock, full of antibiotics and growth hormones. A good soil mix can obtain the nutrient sources from plants and the sea, and when in balance, the nutrients will be released slowly throughout the growth cycle.
Basic Recipe
The basic ingredients for living soil.
Credit: Ben Blandford
• 1-2 parts kelp/alfalfa/comfrey meal
• 1-2 parts neem/Karanja meal
• 1-2 part crustacean/fish meal
• 6-8 parts basalt rock dust
• 2-3 parts gypsum
This should be all mixed together then used at 200-400g per 50L of base soil. If using peat in your base soil mix, you will need to use some limestone to raise the pH, around 4-6g per L of soil mix.
The nutrition in living soil comes from the microbes in the compost that start to feed on the inputs and break them down to their mineral forms so the plants can use them. Until the bacteria have done their work, the minerals are locked up in the amendments, and therefore, the plants do not get overfed. The plants release something called “root exudates” into the soil to attract the different microbes they need to release the minerals they want. It is a trade between plants and microbes - exudates for minerals - working together to help each other. This type of exchange is what soil scientists and ecologists call “mutualism”. When growers bottle-feed organic nutrients, they create a similar blast of microbial activity that causes a flash of nutrition, but it is gone as fast as it comes. A well-made living soil will have continuous availability of nutrition.
Soil cooking with microbial growth.
Credit: Ben Blandford
Another benefit with real organic living soil is that you can introduce worms to your containers and use them as a team of composters and aerators working 24/7 to keep the cycle of nature moving. They don’t eat and digest, but rather filter the decomposing organic matter into its mineral forms and coat it with enzymes that help with the availability of the nutrition. With worms, you can re-use the same body of soil over and over, just like in nature.
With worms, you can reuse the same body of soil, over and over, just like in nature.
Most living soil growers use a mulch layer to cover the surface of the soil, keeping moisture in and allowing root and microbial activity to occur right at the soil surface. Popular materials for mulches are chopped straw, hay, and even stalks and leaves from the previous crop’s waste trimmings. If you can create a good layer of composting nutritious mulch, it will feed the soil as you water. If you have worms in your soil, they will consume the decomposing mulch and create vermicompost on the soil surface.
Worms consume decomposing mulch to create vermicompost.
Credit: Ben Blandford
If growing no-till style with mulch and worms, you will also develop a population of other insects that are beneficial to the living soil system. Don’t be put off by these insects; they will protect your plants and keep things in balance. The most common is hypoaspis miles (now called stratiolaelaps scimitus), which feed on fungus gnat larvae and thrips pupae. They often build up good populations and also commonly come from the compost source, helping you by patrolling for bad guys. There are many other specialist predator species you can use to combat common grow room pests as well to avoid the need for sprays and pesticides.
To get the soil life working well, having more than one plant species growing in the pot can help. Living soil growers often cultivate a "cover crop" such as clover, peas, millet, vetch, and buckwheat. These plants establish quickly and can help fix nitrogen while promoting the establishment and continued growth of mycorrhizal fungi. Cover crops can grow through the mulch layer and help form living mulch. Once the plant canopy is well established, a common technique is to "chop and drop" the cover crop, allowing it to decompose and become food for the soil and microbes and worms.
Cover crop growing through mulch.
Credit: Ben Blandford
Depending what you’re using in your soil mix and the pot size, some growers like to supplement additional inputs throughout the cycle. The easiest and most effective way is often to top dress; this means dusting the soil surface with whatever you choose to use, and then let it get drenched into the soil as you water. Top dressing the same balanced blend of organic inputs and minerals used for the original soil mix is ideal, or you can use other straight dry amendments such as malted barley powder, insect frass, or comfrey powder.
If growing long term in containers, a regular top dressing of amendments and a fresh layer of compost at the start of bloom and again at the end of each cycle keeps everything status quo. If adding some different inputs that you didn’t have in the soil initially, then top dressing is also ideal. Compost teas have been widely used and recommended within the no-till scene. If using compost teas, we suggest making a compost extract instead of a brew. Add compost to water, agitate thoroughly, then apply straight away. This allows the microbial development to happen in the soil, not in a tub of bubbly water. The same can be said about instant microbial teas, which are equally effective.
Top dressing to maintain vitality.
Credit: Ben Blandford
You can also use liquid additives such as seaweed extract, liquid fish hydrolysate or emulsion, amino acids, humic and fulvic acids, coconut water and Aloe Vera extract to name a few. If you are keen on using bloom boosters, be sure to do your research and find out what’s in them. You don’t need to apply PK booster with living soil, but some organic bloom boosters made from fermented plant extracts are compatible. Many no-till growers tend to make their fermented plant extracts using Korean Natural Farming (KNF) techniques.
Of course, anything added should be carefully considered as the quality is of the utmost importance. Do not add something unless absolutely necessary. Keep it simple, and nature will provide.
It is recommended to use four 40L to 50L pots per square metre to provide an adequate reservoir of nutrition for your plants. That’s a total of 160-200L of living soil per square metre of the canopy! Choosing fabric pots with handles is a good option, as the plants remain fairly portable if required. Some growers like to plant cuttings or seedings directly into these final pots, but if it is a new soil mix, then it is often best to have plants already established in smaller containers with a good root ball ready to adapt to its new home.
Alive with activity.
Credit: Ben Blandford
Watering Living Soil
The key to living soil is the moisture level; it is essential not to over or underwater the containers. Because they are much larger than that which growers may be used to, they can hold water longer, and if the plant is still small, it may cause overwatering. When starting with living soil, you need to ease the plant in gradually by watering little and often. A good rule of thumb for watering after planting is 5-10% of the total pot volume (40L pot = 2-4L of water). Watch how they use that water by checking the soil surface over a couple of days, then steadily increase the water volume the more they transpire.
Keep the top wet without water-logging the bottom. Water will sink to the bottom of the pot, which means there is a risk of overwatering while trying to keep the top moist. You may need to use a pump-sprayer or fine rose watering can to moisten the top layer regularly, rather than drench the whole container. While the plants are small it is best to be extra careful, but once in full bloom, they will be able to drink much more. Typically, a grower using 40L pots will be watering each pot up to 2-4L per day, but some plants may even need a bit more every few waterings.
With timer and pump-powered drip irrigation systems, it is highly recommended you know exactly how much water the soil needs in your growing environment before switching to full automation. Autopot irrigation systems that are fed by a valve in the bottom tray or other sub-irrigated planter systems are also suitable for living soils. With systems like this, it’s still important to get the living soil volume per M2 correct (160-200L). It is also best practice to water by hand from the top until the plants need watering every day, then you can automate the bottom feeding. Perhaps the most attractive aspect of growing using living soil and no-till methods is what happens at the end of the growing cycle. Rather than throwing away the soil or adding it to outdoor beds, growers can retain the same containers of soil for re-use. That means no tipping out containers, no dust, and no re-filling. If you look after the soil, it will improve over time, and your harvestable goods will also get better. If intending to re-use the soil from the start, you should already have worms doing their work and a mulch layer creating a compost effect from the top. This way, all that is needed is the addition of new plants as space becomes available. Just dig a little hole and go again!
Mulch layer creating compost.
Credit: Ben Blandford
Reinvigorating Living Soil
If you didn’t plan to re-use the soil but still want to, all you need to do is remix it with some fresh compost or vermicompost, along with a few other amendments. Most growers start with the 40L pots and then end up with 50L once they have added around 10% more compost plus the amendments. When remixing, you will need to empty the container, but don’t worry about removing any root mass, as it will get consumed by the microbes. Depending on the pot size the new mix goes into, it may heat up and feel warm to the touch. This is where the microbes are breaking down the quick release inputs for some immediate nutrition, but it will then start to cool down after 7-10 days and be ready to use. Planting a cover crop and waiting to see if it comes up green and healthy is an excellent way to tell if the soil is ready for the main crop. Some companies now sell amendment kits that include everything you need to re-amend used living soil, but remember; it is important to start with highquality living soil, not just regular potting soil.
When the soil life is well-fed and in harmony, the plants will grow themselves. Use what is available locally and don’t over complicate anything unnecessarily. Just remember to start with high-quality organic soil, and you will already be halfway to having abundant, glorious produce for your effort!
