Filthy, Stinking, Rich Dirt

Worm Castings

So you aren’t ready to go all-in on a worm bin. But your plants can still benefit from the wrigglers’ manure. Combine it with your soil mixture or with water to make a compost tea—­a brown fertilizer liquor of sorts—to spray onto leaves.
Best for: Potted plants, which are more easily burned by chemical fertilizers. $36.86 for 30 lbs. at Hydrobuilder

Coco Coir

The inner husks of ­coconuts improve drainage by creating air pockets while simultaneously sponging up moisture in otherwise quick-draining, sandy soils. Coco coir is also a sustain­able, pH-­neutral ­alternative to peat moss, which is highly acidic and takes centuries to replenish.
Best for: Herbs. Coco coir doesn’t add any nutrients, but most herbs taste better grown in ­nutrient-poor soils, anyway. $36.95 for an 11-lb. block at Eartheasy

Kelp Meal

This dried, ­pulverized form of seaweed adds organic matter to soil and delivers minerals and enzymes. It swells up when wet, which helps dirt retain moisture. Think of it as an investment, not a quick fix, to improve the quality of soil over time.
Best for: ­Lettuce, potatoes, and other potassium-­loving plants. $29.95 for 4 lbs. at Gardener’s Supply Co.

Alfalfa Meal

Because it pulls nitrogen out of the air and fixes it in the soil—a neat trick of pea-family plants—alfalfa is often used as a cover crop. In dried and powdered form, it’s just as effective at adding nitrogen and trace minerals.
Best for: Roses. Alfalfa meal contains ­­triacontanol, a growth hormone that’s especially effective on the flowers—and thus, on such others in the rose family as strawberries, blackberries, pomes, and stone fruits. $14 per lb. at Greenway Biotech

Greensand

An outstanding amendment (and indeed, a lovely shade of green) that sometimes goes by the name glauconite, this iron silicate is a great source of potassium to make most plants more vigorous. It can also improve the texture of a heavy clay soil, helping it retain moisture better.
Best for: Cucumbers and melons. The potassium helps them produce fruit. $26.95 for 6 lbs. at Woodies Garden Goods

Zeolite

If you have a set-it-­and-­ forget-it mentality, this all-­around soil savior is for you. It reduces the need for water by improving moisture retention in sandy soils and ­upgrading aeration in heavy ones.
Best for: Plants that are sensitive to heat stress, such as pumpkins, squash, and beans, which prefer the cooler temperatures of damp soil. $16.97 for 5 lbs. at Home Depot

Azomite

If sea minerals mixed with ancient volcanic dust sound like something you’d pay a lot to soak in, think how your heirloom varietals will feel.
Best for: Peppers. Studies show that Early Perfect Italian and other roasting varieties had significantly higher yields when azomite was added to the soil. $14 per lb. at Greenway Biotech

Langbeinite

Often labeled as sul-po-mag, it’s found in ancient ocean beds in the U.S. Southwest. The mineral provides a unique source of sulfur, potassium, and magnesium, useful when you need a micronutrient boost without adding calcium or changing the soil’s pH balance.
Best for: Salt-sensitive ­pansies and zinnias, which respond to added calcium with wimpier, weaker blooms. $13.39 for 5 lbs. at Arbico Organics

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