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5 Soil Amendments to Grow Better Herbs

Culinary flair starts in the garden. Use these tips to build healthy soil your herbs will love.

By Jan Berry


5 Soil Amendments to Help You Grow Better Herbs - Photo by Rachael Brugger (HobbyFarms.com)
Photo by Rachael Brugger

Herbs can be a gardener's best friend, but only if you give them a nice spot to call home. While they’re generally easygoing and will grow in less-than-ideal conditions, properly prepared soil will ensure the most exceptional flavors and harvest. Before planning and planting any garden, it's helpful to know more about the foundation you're working with—aka, your soil.

Garden soil falls loosely into three categories: clay, sand and loam. Clay is heavy and compact, leaving little room between soil particles for oxygen and water to easily pass through. Plant roots tend to suffocate or drown in these conditions. In contrast, sand has such large spaces between soil particles, water drains rapidly through, robbing roots of the essential nutrients they need. Loam, the ideal garden soil, is crumbly and light, has good drainage, and allows roots room to breathe and grow. This is the soil we strive for.

To determine which of these types you have, scoop up a handful of moist dirt from your garden and try to squeeze it into a ball by making a fist. Open your hand and observe what happens. If it falls apart right away, it's sandy. If it holds its shape, including where you pressed your fingers, it's clay. If it formed a ball that crumbles into smaller chunks when gently poked, you have loam.

If you have extremely poor dirt, it doesn't mean that you're doomed to grow nothing but weeds. The following five soil amendments will improve the drainage and structure of both sandy and clay soils. Once a friable loam state is reached—and this may take a few years—organic matter should still be worked in annually to maintain soil quality.

1. Compost
Compost, sometimes called black gold, is created when vegetable scraps, egg shells, pine needles, grass clippings, straw, wood chips, garden waste and other organic materials are allowed to decompose in a controlled manner. You can make it at home or, if a larger supply is needed, buy it in bags at your local garden center. Commercial compost varies widely in quality, so research your choices thoroughly before purchasing.

A good starting point is to spread at least 1 to 2 inches of compost over your entire growing bed. More is better when it comes to adding compost to poor soil. Using a garden fork and shovel, incorporate this into the top 6 to 9 inches of dirt. This method requires a good bit of initial labor, but your soil will become increasingly easier to maintain as its quality increases over time.

2. Worm Castings
Worm castings, or vermicompost, serve a similar purpose as ordinary compost by improving the overall structure of your soil. As a bonus, it acts as an effective fertilizer that won't burn plants. The caution here is to be strategic with its use. Some herbs, such as borage, hyssop and thyme, are less flavorful when soil is too rich. On the other hand, calendula, mint, lovage and parsley will enjoy the extra nutrients. (See the list below for growing details of individual herbs.)

Raising worms for their castings doesn't require a lot of expertise or fancy equipment. For this reason, it makes a great project for interested kids and space-crunched apartment dwellers. For an overview of everything you need to know to start your own worm bin, see this helpful brochure on the Shedd Aquarium website or watch this HobbyFarms.com video.

3. Manure
Manure from farm animals (not dogs or cats) should be well-aged for about six months or composted before adding to your soil. As an alternative, some gardeners spread fresh manure over an empty garden bed in the fall, then turn it under in the spring before planting. The drawback of doing this is a risk of undigested seeds causing a weed outbreak in your garden. 

Depending on how the animals are raised, manure can sometimes contain buildup of persistent herbicides that aren't broken down by sunlight or composting. To avoid these substances in your garden, it's best to seek out a supply from a farmer who treats their land and animals naturally.

4. Peat Moss
Peat moss is a good soil conditioner that can help lighten clay soil while adding body to sandy soils. It's comprised of partially decomposed plant material that accumulates over centuries in boggy areas called peatlands. Most of the peat moss in the United States comes from Canada, where it's responsibly harvested, but one should still keep in mind that it's a slow-growing natural resource to be used in respectful moderation.

Like compost, it can be tilled into your garden bed before planting, but unlike compost, it will acidify your soil. This is a good quality if you're growing acid-loving blueberry plants, but undesirable for herbs that prefer more alkaline soil, such as rosemary and oregano.

5. Leaf Mold
Leaf mold is an excellent substitute for peat and can easily be made right in your own backyard for no cost other than a little up-front effort. It does, however, require at least one deciduous tree and a healthy dose of patience.

To make your own leaf mold, gather freshly fallen leaves in a wire bin or wooden enclosure. Unlike compost, you don't need to worry about heat or constant turning. Just pile the leaves up, moisten them during dry times, and leave them mostly alone for about a year, or possibly longer. Shredding the leaves with a lawn mower before adding to bins or covering the pile with a tarp are ways to speed up the decomposition process.

As an alternative to a bin, you can collect leaves in trash bags and moisten them well. After tying closed, poke several holes in the bag for air flow. Stack the bags in an out-of-the-way spot, and allow nature to take over the process. After enough time has passed, you'll be rewarded with an earthy, crumbly, leafy mixture like you’d find on the forest floor.

When dug into the garden, leaf mold improves soil structure. It can also be used as a top dressing or mulch for plants.

Know Your Herbs
While most herbs share a common love for well-drained soil and full sun, they have varying preferences and requirements. Below is a list of common herbs along with brief growing notes that may prove helpful when planting.

  • Basil: rich, well-drained soil; full sun
  • Bee Balm: average, well-drained soil; full sun
  • Borage: less fertile, dry soil; full sun
  • Calendula: rich, well-drained loam; full sun
  • Chamomile: well-drained, moist soil; full sun to part shade
  • Cilantro: well-drained, fairly rich soil; full sun
  • Comfrey: average soil; full sun
  • Echinacea: average, well-drained soil, only water during severe drought; full sun
  • Hyssop: ordinary soil (rich soil will produce luxurious growth, but less flavor and aroma); partial shade
  • Nasturtium: ordinary garden soil; rich soils makes for few blooms; full sun or partial shade
  • Lavender: dry, well-drained soil; full sun
  • Lovage: rich, well-drained soil; full sun to part shade
  • Mint: moist, rich, well-drained soil; prefers partial shade but will grow in full sun
  • Oregano: dry, well-drained, alkaline soil, not too rich; full sun
  • Parsley: moderately rich, well-drained soil; full sun to partial shade
  • Pineapple Sage: light, sandy, well-drained soil; full sun
  • Rosemary: alkaline, well-drained soil; full sun to partial shade
  • Sage: light, sandy, well-drained soil; full sun to light shade
  • Summer Savory: dry, sandy soil, with added organic matter; full sun
  • Thyme: poor, well-drained, rocky, alkaline soil; full sun (rich soil makes less flavorful leaves)
  • Yarrow: average, well-drained soil; tolerates poor soil and drought; full sun

Get more herb-growing tips from HobbyFarms.com:

About the Author: Jan Berry lives on a small hobby farm in the Blue Ridge mountains of Virginia with her husband, two children and assorted collection of goats, ducks, chickens, bunnies, dogs and one cat—aptly named Rascal. You can find her online at www.thenerdyfarmwife.com.

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5 Soil Amendments to Grow Better Herbs

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Reader Comments
Hi Wendy, That's a great question. You're correct - leaves are a good addition to the compost pile too.

The benefits of letting leaves decay all on their own though, is that the resulting product (leaf mold)has its own special qualities. Leaf mold is better at absorbing water than just regular compost - up to three or four times its weight. This is why it's an excellent substitute for peat moss. Because it's strictly carbon based (from leaves only) it has a different and more subtle nutrient profile than nitrogen containing compost. Leaf mold is broken down slowly ("cold" decomposition), whereas compost is created using a "hot" method. In the fall, many people have far more fallen leaves than a compost pile can hold, so separate leaf bins or bags for making leaf mold is a good use of the extra.

While those are a few differences, I also listed leaf mold separately to hopefully help draw a bit of extra attention to it since it doesn't always get the press that compost does. I appreciate your thoughtful question and for giving me the opportunity to talk about it a bit more!
Jan, The Nerdy Farm Wife, VA
Posted: 5/14/2014 5:27:24 AM
I don't understand why you would handle leaf mold like that & not just compost it with everything else.
wendy, Round Rock, TX
Posted: 5/12/2014 5:58:54 PM
Good article!
Randy, Van Buren, AR
Posted: 5/1/2014 5:45:33 AM
Thank you! I'm clipping this article to file with my Herb Growing Guide.
Dante, Hyde Park, MA
Posted: 4/30/2014 1:07:45 PM
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