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Refreshing Raised Bed Soils Using Sunshine Community Garden’s Custom Recipe

4/19/2021

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In this video Charlotte from the SCG Education Team gives a breakdown of Sunshine Community Garden’s custom recipe for refreshing raised bed soil that has been depleted or sitting without proper protection from the Texas heat. This volunteer project by members of the Sunshine Community Gardens was at the Texas School for the Blind and Visually Impaired Garden which is also located at Sunshine. This soil refresh recipe is perfect for school or community garden beds, container gardens, or any raised beds that have been sitting unused for a period of time. Many of these tips apply to all soil amending in central Texas, even for in ground beds. 
​
PLANNING
  1. All stages of this work require a dust mask and gloves for all workers.
  2. Think in terms of the volume of “spent” old soil mix to new mix. Aiming for a ratio of 50:50 is a good rule of thumb but you can vary this by your situation and budget. Try for at least 2/3rd of the old soil mix to 1/3rd amended mix.
  3. A good portion of the renewal mix should be a good quality compost, whether purchased or homemade, since this is the best resource for the new “living” components of your renewal mix. The kelp meal we use in this recipe provides food for our renewed soil’s living community.
  4. If worms are encountered at any time during the process, carefully set them aside in a good amount of moist soil to protect them from the “mixing” steps. Gently reintroduce them to the refreshed bedding mix after it has been returned to the box or raised bed.
  5. A bed that is going to rest for a season is built slightly differently than one that you are going to use right away. You do not want excessive compost activity to compete for nitrogen during your plant’s growth stage, especially the green growth prior to the fruit setting stage, so you may need to add your favorite more immediately available amendments near new plants so that they neither compete, nor wait, for slower releasing components. 
  6. Prior to mycorrhizal reformation in the soil, which will take some weeks, your transplants may need more water too since these networks must form to extend your plant root’s “water reach” and improve drought tolerance.
  7. These mycorrhizal networks are part of your “soil food web” which needs time to establish following all of the mixing disturbance of this refresh method. These networks will regenerate and establish their symbiotic relationship with your plant roots becoming their nutrient and water “help mates.”  
  8. Refreshing raised beds is also possible using “lasagna” (or similar) no till methods by adding refreshed layers regularly each season. This will be covered in a future video.

RECIPE
The following is Sunshines Community Garden’s custom soil refresher recipe. It does not require precision and the amounts are approximate.

Major components
6 – 10 parts        spent (previous/old) old bedding mix
4 - 5 parts            compost
1 part            rice hulls (premoistened)
1 part            shredded coconut coir (premoistened overnight if possible)
½ part             kelp meal (i.e., use ½ to all of a 5lb box from Down To Earth)
½ part             perlite (optional, i.e., use ½ to all of an 8-quart bag) 
½ part            diatomaceous earth (optional)

Mineral Amendments
Add by the cup or by the handful. Use product packaging or the internet for reference:
  • Green sand – very slow release micro mineral
  • Azomite – very slow release micro mineral (or get the powder for faster release)
  • Sulfur pellets – slow release acidifier
  • Magnesium Sulfate (Epsom Salt) – rapid release – makes calcium available 

Optional Amendments 
Best added on top of refreshed soil for more immediate availability:
  • Worm castings
  • Seaweed spray
  • Fish emulsion spray
  • A balanced, gentle “N-P-K” meal or granules: Down to Earth or Jobe’s 

BREAKDOWN IN STEPS
STEP 1:
On a tarp, remove old soil from beds into piles of around one-fourth cubic yard each (30-40 gallons) to make mixing easier. In the video we give a suggestion for cases when it is not possible to amend all of the old soil by inserting the compostable layer (normally at the bottom of a raised bed) above any soil that will not be amended. Amend 100% of shallow beds but 50-70% of deeper beds is fine if you have time or budget limitations.

STEP 2: Next to the pile of old bedding mix, start with a separate pile, with compost, close to the same size (20-30 gallons.) Any type of organic compost works and we chose to use turkey compost. 

STEP 3: Add a significant amount of nitrogen-rich structural amendments that will break down more QUICKLY (in 1-2 seasons.) These types of organic matter are often agricultural by-products and can be free or inexpensive. Follow our recipe, product packaging or internet to determine the amount to add.

While certain amendments (like rice hulls, coconut coir or diatomaceous earth) are best pre-moistened before adding them, it is easier to mix your piles if everything is drier. 
  • RICE HULLS – A combination of structure (temporary in hot climates) & nutrients including silica. Silica strengthens cell walls, guards against environmental stress, improves the uptake of water and minerals and adds an extra level of protection against diseases like powdery mildew.
  • COTTONSEED MEAL  –  Cottonseed meal feeds nitrogen, potash, phosphorus, and other micronutrients over a period of time, eliminating runoff, and promoting vigorous growth
  • DIATOMACEOUS EARTH (DE)  –  Water retention and reduces amendment leeching. (See section at the end on amendments that can be confusing.)
  • SPENT MUSHROOM BLOCKS  – A waste product from growing culinary mushrooms. The blocks, composed of sawdust and grains, are colonized with mycelium which is high in nitrogen, carbon, phosphorus and trace minerals. It will increase the water-holding capacity of the soil. To get mushroom compost blocks for your garden, sign up here.
  • COFFEE CHAFF  –  A waste product of the coffee bean roasting process. Coffee chaff wards off harmful slugs and snails. Coffee chaff adds helpful nutrients, like nitrogen. On the other hand, brewed coffee grounds require nitrogen to breakdown in the soil so do not use brewed grounds as a structural element in refreshing soil. (See section at the end on amendments that can be confusing.)
  • KELP MEAL – Seaweed or Kelp Meal adds potassium (K), trace minerals, salts, alkalinizing the soil. It's an excellent bioactivator, waking the microbes in the soil to help break down organic matter. Add kelp meal at this “significant volume” but quicker break down stage, if using:

STEP 4: Add a significant amount of structural amendments that break down SLOWLY such as coco coir, peat moss, perlite and vermiculite. Follow our recipe, product packaging or internet to determine the amount to add. 
  • COCO COIR – Coconut Coir is a natural fibre extracted from the outer husk of coconut and has a neutral pH range of 5.2–6.8. 
  • PEAT MOSS – Peat takes millennia to generate, and bogs store 10 times more carbon than forests. Coco coir is more sustainable but needs to be shipped from a distance.
  • PERLITE & VERMICULITE - Extremely slow breakdown near zero. Commonly used in commercial potting and bedding mix formulations with coir or peat. These are used to  improve aeration of the soil, promote consistent release of added fertilizer and improve moisture retention. 

STEP 5: Add minerals & silica for nutrition and cell structure. Follow our recipe, product packaging or internet to determine the amount to add. 
  • TEXAS GREEN SAND – slow-release trace minerals. Texas greensand (Glauconite) is an iron potassium, silicate that is green in color due to the minerals it contains. Greensand is a marine deposit that contains traces of many if not all of the elements which are in seawater. It has been used successfully for enriching soils for over 100 years. 
  • AZOMITE, EXCELERITE – Azomite is a natural volcanic mineral which is mined from the Utah desert and contains trace minerals. It has been reported to improve root systems, yields and general plant vigor in a variety of applications; from field crops and orchards to lawn and garden use. 
  • EPSOM SALT – Magnesium sulfate allows plants to take in these valuable nutrients including calcium, nitrogen and phosphorus. Ratio Ca 7-8 : Mg 1
  • SULFUR PELLETS – Sulfur, when converted by bacteria to sulfuric acid, lowers soil pH (acidifies), increasing plant-root access to many nutrients. Sulfur plays a critical role in the formation of plant tissue proteins and vitamin formation and is essential to the flavor of onions, garlic and other alums. For most garden annuals, vegetables and perennials, your goal is to create neutral-to-slightly-acid soil, with a pH of 6.5 to 7.0 . 

STEP 6: Mix enriched pile of amendments until all components are uniformly distributed. 

STEP 7: Combine old soil with enriched amendment pile. As you return your refreshed bedding mix to your box or containers, moisten each layer as you go so that your final result is moist enough to form a loose but distinct clump when squeezed in your hand.
 
STEP 8: Add cardboard on bottom of the bed or on top of left-over soil. This prevents weeds and adds more worm food. 

STEP 9: Add leaves or other brown and green debris (carbon) and coffee (attracts worms) on top of cardboard. Water this layer.

STEP 10: Fill bed with half of the renewed bedding mix, followed by a watering, and then fill with remainder with another watering.

STEP 11: Top mulch the bed with any of the following types of mulch to help retain moisture. Some of these will continue to add nutrients to the soil:
  • ALFALFA HAY - High in nitrogen and long lasting.
  • LEAVES -  Collect them in the fall and the more decomposed or “moldy” the better for your garden. 
  • WHEAT STRAW - Make sure not to use hay because it contains seeds.
  • PINE NEEDLES -  Helps create a more acidic soil.
  • HARDWOOD MULCH - Avoid cedar mulch. The oils from the cedar are antimicrobial / antifungal which you don’t want to disrupt in the soil
  • WOOD CHIPS - Do not mix into the soil because the decomposition process requires nutrients and will steal them from your plants.

MORE ORGANIC AMENDMENTS 
SEAWEED OR KELP MEAL
– Seaweed or Kelp Meal adds potassium (K), trace minerals, salts, alkalinizing the soil. It's an excellent bioactivator, waking the microbes in the soil to help break down organic matter.
SEAWEED SPRAY (alkalinizing) Alternatively, mix in a few handfuls of dried kelp meal.  Supposedly helps with heat tolerance but cannot find a reference for that yet. NOTE:  Excessive potassium or potash will decrease the soil's acidity so use it in a balanced way.)
FISH EMULSION  –  A fast-acting, organic liquid fertilizer made from the byproducts of the fishing industry. It is rich in nitrogen, phosphorus and potassium, plus trace elements such as calcium, magnesium, sulfur, chlorine, and sodium.
SHRIMP MEAL –  nitrogen, phosphorus, calcium, and chitin
CRAB MEAL, OYSTER OR LOBSTER  – nitrogen, phosphorus, calcium, and chitin
BONE MEAL – phosphorus “roots and fruits”
BLOOD MEAL – nitrogen “greening the giant”
ORGANIC N-P-K SLOW-RELEASE GRANULES  –  Down to Earth or Jobe’s 
WORMS
WORM CASTINGS
INSECT FRASS  –  Mealworm castings, cricket frass, is simply the feces of the insect. 
ROCK DUST (and/or regular sand) – very slow-release minerals and SOME water retention. (Less sophisticated than Azomite, Excelerite or Green Sand)
LIME - Generally not needed in central Texas because it is too alkalinizing

AMENDMENTS THAT CAN BE CONFUSING
Biochar (alkalinizing) “potash”–  If you're adding potassium to decrease the soil's acidity, use 1 to 2 pounds of hardwood ash per 100 square feet of soil. Other ways to add potassium are: add cut up banana peels and bury them 1 to 2 inches down in the soil or mix in a few handfuls of dried kelp meal or spray the soil with a liquid seaweed spray.

Coffee grounds – Brewed grounds are pH neutral but they do consume nitrogen as they decompose and compete with growing crops…but worms are mad for them. Some gardeners drop into vertical “wells” so worms can visit without significant contact with growing plant roots. ONLY UNBREWED COFFEE GROUNDS ARE ACIDIC.

More Epsom Salt for tomatoes, peppers or calcium loving plants at the time of transplant and for maintenance

Food Grade Diatomaceous Earth (FG-DE) is derived from fossilized remains of algae-like, single-cell plants called diatoms. Diatoms are some of the oldest plants in the world. They date back millions of years. These plants left behind chalky deposits called diatomite which is ground into a powder and purified for the consumer market. Chemically speaking, diatomaceous earth is 84% silica, and contains some 20 trace minerals, including small percentages of magnesium, sodium, iron and a good dose of calcium in the right ratio with magnesium for good utilization in building structures such as cell walls for healthy leaves and stems. In humans and animals, silica is essential for the building of healthy bones and teeth, skin, hair, and nails.

FG-DE is often used in the garden as a natural pest control substance. However, it can harm bees, other pollinators and ladybugs so use proper precautions as needed to reduce the chances of harm such as only using when needed for a specific pest, not over applying and avoiding use on vegetables and pollinator plants that are flowering.

Many studies have also been conducted to analyze the effect that FG-DE has as a soil amendment. These studies have shown promising results, suggesting that diatomaceous earth may significantly enhance nutrient retention and moisture retention in soil. https://www.absorbentproductsltd.com/food-grade-diatomaceous-earth-as-a-soil-amendment/ 
So far the conclusion is that diatomaceous earth doesn’t harm most beneficial microorganisms in the soil. Worms, for example, are not affected by the microscopic edges in diatomaceous earth particles.


 WHERE TO BUY AMENDMENTS
We recommend the following local garden store for many of the amendments in our recipe. Austin Organic Gardeners, Sunshine Community Gardeners and other Austin area community gardeners are eligible to receive a discount at: 

Brite Ideas Aquaponics, Hydroponics and Organics
South Austin (NEW LOCATION)
12110 Manchaca Rd. Ste. 103
Austin, TX 78748
Local: 512.444.2100
Owner: Troy Smith

SOUTH AUSTIN STORE HOURS (CLOSED ON MONDAYS)
Tuesday-Friday 10:00 am – 6:00 pm
Saturday 10:30 am – 5:00 pm
Sunday 12:00 pm – 4:00 pm

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