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Raised Beds: Respecting the Law of Return

By: Maureen Gilmer

To enrich a full raised bed, use low volume, high potency organic fertilizers before planting time in early spring.

If you’re growing vegetables in raised beds, you must respect the Law of Return.  This law states that nutrients extracted from the soil by growing plants must be compensated for by tilling their dead remnants back into the soil or fertility loss will result.  Because plants are often grown more densely in small or raised beds, proportionately more nutrition is drawn from the soil each year than in in-ground gardens.  The chances of running a deficit are very real, and your plants will show it, but by then it’s too late.

The challenge of raised beds is that there’s no room for adding gobs of compost to the box because it was filled to the top in the first place.  The fertility of all raised beds will decline each year unless you return it with fertilizer to compensate for these losses.

Add Organic Matter

High-density gardening in raised beds draws proportionately more nutrition from the soil over the course of each season.

To keep microbe populations high, organic matter is needed.  If your potting soil is decomposing so the soil level has dropped, can you refill it with any of the Black Gold potting soils with RESiLIENCE® or just use Black Gold Garden Compost and work it into the old stuff.  But if your soil mass is maxed out, use fertilizers that provide higher levels of nutrition without much volume. Older soilless mixes can also acidify, which will inhibit plants from taking in needed nutrients while reducing soil microbes and overall soil health. A simple soil pH test should be conducted to determine soil acidity/alkalinity. To return acid soils to a  neutral ph is ideal, a liming agent is required.

Fertilize

Organic fertilizers are slower to become available to plants than synthetics, so preparing your raised bed soil well in advance of planting time.  Fall is ideal, but early spring works just as well.  This allows time for the various raw materials to decompose, interact and create the synergy between plants, microbes, and earth to give your garden everything it needs, naturally.

For gardens where there’s little space, two organic fertilizers offer everything needed to fuel this year’s vegetable crops.  They’re like ordering a la carte or choosing a combination plate at a Mexican restaurant. The combination is a tomato & vegetable fertilizer with added alfalfa meal.

An organic tomato & vegetable fertilizer, with a balanced ratio of nitrogen, phosphorus, and potassium should be added.  Estimate at least one bag of fertilizer for each 4′ by 8′ raised bed to calculate how much you need.

Rose growers have always been keen on using alfalfa Meal a la carte, which contains about 3% nitrogen plus other benefits.  What makes it doubly valuable is that alfalfa is a legume, a nitrogen-fixing plant, so all of its remnants from baled hay to this byproduct of milling also contain vestiges of the mycorrhizae, unique fungi that live symbiotically within these plants.

To apply these fertilizers, spade up your raised bed with a fork to open it up a foot or so deep, then sprinkle the fertilizers evenly over the soil.  Let them filter down into the nooks and crannies, then spade over each bed again to help the soil tighten around the fertilizer.  Once thoroughly blended, rake the surface smooth so it’s ready to plant.  Water deeply, if there has not been sufficient rain.

The Law of Return

Replenished raised beds perform better!

The longer the garden sits after you’ve returned nutrients to the soil, the more fertile it becomes.  As temperatures warm, microbes activate and enrich the soil further.  So when it’s time to plant your peas in March, and anything else after that, complying with the Law Of Return will guarantee you vegetables show their appreciation with the most generous harvests you can imagine.

About Maureen Gilmer


Maureen Gilmer is celebrating her 40th year in California horticulture and photojournalism as the most widely published professional in the state. She is the author of 21 books on gardening, design and the environment, is a widely published photographer, and syndicated with Tribune Content Agency. She is the weekly horticultural columnist for the Desert Sun newspaper in Palm Springs and contributes to Desert Magazine, specializing on arid zone plants and practices for a changing climate. She works and lives in the remote high desert for firsthand observations of native species. Her latest book is The Colorful Dry Garden published by Sasquatch Books. When not writing or photographing she is out exploring the desert on her Arabian horse. She lives in Morongo Valley with her husband Jim and two rescue pit bulls. When not writing or photographing she is usually out riding her quarter horse.

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