The Dirt on Saving Water in the Garden: Good Soil

Gardeners can take many steps to save water, such as saving rain water and using drip irrigation. But one of the most crucial steps lies beneath our feet, in the soil that protects and nourishes roots and controls water drainage and aeration.

black sand beach Maui
Black sand in Maui along Hana Highway. The black sand is made from lava rock.

What you can’t see: soil microbes

Tiny microbes feed soil and plants, relying largely on humus, the rich organic matter that results from decay of natural materials. When conditions are right, insects, earthworms and microorganisms in healthy soil create humus. Organic matter in the soil ensures that microbes thrive and the soil drains as it should. And when a plant is otherwise healthy, it’s less vulnerable to diseases and can likely survive with less water. In Master Gardener training, I learned that New Mexico soils have organic matter of 20 percent or lower on average. At our place, rocks take up 90 percent of the soil (slight exaggeration). We located our vegetable garden in an area that used to be part of an apple orchard and that’s near the river. The soil is much better than near the house, likely because of organic matter working its way into the soil over the years.

xeric rock garden
Got rocks? We’re certain the rock garden walls and borders were made with rocks excavated on our land! Many of the native and xeric plants have adapted to soil conditions.

Xeric plants and soil drainage

The thing is, many xeric plants are more affected by soil that remains wet than by lack of water. Lavender comes to mind; wet feet can cause root rot. Add a sudden drop in temperature to the dampness and lavender plants are at risk of dying. I’m seriously worried about ours after 18 inches of snow. Plant care instructions for nearly all xeric plants read “place in well-draining soil” because too much water in the soil suffocates a plant’s roots. Sand dries too quickly, but clay and compacted soils fail to drain.

Lavender does better with well-draining soil and less water.
Lavender does better with well-draining soil and less water.

Plants use valuable energy to pull moisture from soil. When they have to work harder to access water in soil, plants become stressed and wilt. If your soil drains quickly, you have to water more often and less deeply. Loam is the name used for balanced soil that has a fairly even mix of sand, clay and silt. As mentioned, clay soils hold too much water. Amending either extreme (sand or clay) with organic matter helps plants access the appropriate amount of water needed with less stress. Instead of adding sand or clay to balance soil, gardeners should use organic matter to gradually improve soil health and function.

This soil at the entrance to our vegetable garden is compacted foot traffic. Notice how water from snow melt stands in the soil.
This soil at the entrance to our vegetable garden is compacted from foot traffic. Notice how water from snow melt stands in the soil.
Only a few feet away is this raised bed with organic matter added. No standing water under the same conditions; the water is working its way down through the soil.
Only a few feet away is this raised bed with organic matter added. No standing water under the same conditions; the water is working its way down through the soil (and rocks).

Here are a few tips for ensuring your plants’ soil is healthy, providing nutrients, water drainage and oxygen to roots:

Add organic matter. The type of matter you add is more specific to your soil’s pH and other factors. But most natural organic amendments, such as manure or green manure, can help.  Also called cover crops, green manure is the purposeful planting in fall and winter of crops that restore soil nitrogen and organic matter used up by summer plants. When using animal manure, add it to compost or make sure it’s cooked completely; don’t add fresh manure to growing plants.

You can see the difference in the color and texture of the mushroom compost that sits on top of the summer vegetable bed. The soil needs some help.
You can see the difference in the color and texture of the mushroom compost that sits on top of the summer vegetable bed. The soil needs organic matter from the compost and some broken-up plant residue.

Properly handle plant residue. Although some schools of thought are in favor of letting spent plant material stay on the ground to decay and provide organic matter, gardeners should use caution. Insects overwinter in plant residue on the ground (good if you want monarchs, but you can’t really go around selecting which insects get to take up residence). And it’s never a good idea to use diseased plant material. We kept some healthy plant material, but anything that looks funky goes into compost bins or garbage. We don’t mess with “wilder” areas around the property.

An unripe pear and leaf material remain under a large, old pear tree. They'll compost and improve soil, but also attract ants and other insects.
An unripe pear and leaf material remain under a large, old pear tree. They’ll compost and improve soil, but also attract ants and other insects.

Use organic mulches. Adding mulch around (but not against) the base of the plant helps slow water evaporation from the soil. Organic mulches eventually break down, improving soil make-up.

Here at the Los Angeles County Arboretum and Botanic Garden, landscapers have added mulch around many beds, including blue fescue.
At the Los Angeles County Arboretum and Botanic Garden, landscapers have added mulch around around many plants, including blue fescue.
Cacti at the Arizona-Sonora Desert Museum in Tucson, Ariz. need no mulch!
Cacti at the Arizona-Sonora Desert Museum in Tucson, Ariz. need no mulch!

Rotate crops and use cover crops. In vegetable and herb gardening, move annual crops around so that the soil nutrients get a break. Families of plants differ in how they use soil nutrients.

Stop tilling. Rototilling, the traditional farm method, burns off carbon and adds to weed emergence. It also breaks soil up into smaller particles, which makes it less permeable for air and water. Repeated tilling leads to loose top soil. Heard about the Dust Bowl? Work added organic matter into the top few inches only, or let it sit on top of soil.

When in doubt, test your soil to determine how much of it is sand, clay or loam. You can perform your own home test pretty easily using a mason jar, as described on page 11 of this publication from the San Diego County Water Authority.

 

Our Garden is Hard at Work This Winter

Winter is tough for gardeners who live in zones with shorter growing seasons. In New Mexico, we can typically get outside in winter to work on between-season chores because we usually have dry, sunny conditions. Not so much this year. We’ve had unusual cold, wind and now about 18 to 20 inches of snow.

Our latest snow covered many xeric plants in the garden and keeps wildlife from eating grass and insects on the ground.
Winter storm Goliath dumped at least 18 inches of snow that covered many xeric plants in the garden and keeps wildlife from eating grass and insects on the ground.

Even with snow and cold, there are a few things gardeners can do in winter to satisfy their outdoor cravings and grow a bit of their own food. And our gardens certainly don’t rest all winter; with a little help, the soil rebuilds to nourish next year’s plants. Dormant or dried plants feed wildlife while their food is scarce.

Extend the season with row cover

Like I said, most winters are relatively mild in New Mexico. Although nights in the high desert cool considerably, the days can warm up to at least 50 degrees F. I covered an existing carrot trough to keep the carrots from freezing; they keep much better in the ground than anywhere I can store them once harvested. If you live in zone 8 or warmer, you can grow carrots in winter. We’re trying a new crop and storage/preservation of an established crop in our trough planter.

These carrots were planted in late summer and we're still harvesting after Christmas.
These carrots were planted in late summer and we’re still harvesting after Christmas.

We constructed a small hoop house with row cover cloth to extend the season for early spring or late fall. We spread our carrot, lettuce and spinach seeds inside the hoop tunnel in fall and had a really good germination rate. The carrots are growing slowly, however, and I hope to plant them a little earlier next year. Then again, I also hope for a warmer winter.

We got hoops and row cover cloth from Johnny's Seeds. I've harvested spinach and lettuce. The carrots are growing slowly, but hanging in there.
We got hoops and row cover cloth from Johnny’s Seeds. I’ve harvested spinach and lettuce. The carrots are growing slowly, but hanging in there.
Considering this winter has brought many nights below 20 degrees F, the covered hoop house appears to be working.
Considering this winter has brought many nights below 20 degrees F, the covered hoop house appears to be working.

Prepare the vegetable garden for spring

Before the snow came, we got outside a few times to at least prep our vegetable and herb gardens for next spring. We didn’t have a chance to plant cover crops, and that’s on our list as a strategy for next year in part of the garden. But we want our gardens to rebuild important soil nutrients, so we pulled up some of the frost-bitten plants. Any that looked unhealthy went into a weed pile, but we added much of the material to our compost bin, and left some in the garden. We chopped up the healthy plant material left in garden rows to help it break down faster.

A friend introduced us to mushroom compost, and it's our favorite choice for amending soil and fertilizing grass.
Although we would prefer to buy fresh compost in bulk, there are no certified compost sources nearby. We have to buy these bags in Albuquerque and transport them down. Mushroom compost is our organic matter of choice for building beds and fertilizing grass.

Although we compost, we don’t generate enough to cover our entire vegetable garden, so we purchased mushroom compost, our favorite organic matter. We busted up compacted dirt and built the beds up so they’re slightly raised. Next, we used a small cultivator to work the compost into the top few inches. It’s not the same as tilling, which turns up deeper soil and weed seeds. We’d love to cover the beds with leaves or other mulch, but the wind rules that out. So we used plastic or black fabric cloth on hand. The purpose is mostly to keep weed seeds from blowing onto our clean beds and taking root. In spring, we’ll add a little more compost and mix the soil lightly a few weeks before planting.

Tim works the mushroom compost gently into a row.
Tim works the mushroom compost gently into a row.
We ran out of plastic, which we prefer so that sun reaches the soil. So we used black landscape fabric on one bed. We'll see how they compare in the spring.
We ran out of plastic, which we prefer so that sun reaches the soil. So we used black landscape fabric on one bed. We’ll see how they compare in the spring.

Leave some plant material for wildlife

Schools of thought about fall garden clean-up differ. On the one hand, the more leaves and other plant material you leave on the ground, the higher your chance of insects and weeds using your garden as their winter home. And I agree in many ways with that school of thought. We didn’t want the mess of dried annuals everywhere, and I wouldn’t want a giant pile of leaves up against areas of the garden or house.

Our garden and landscape are partially wild in winter, just enough to help feed wild turkeys!
Our garden and landscape are partially wild in winter, just enough to help feed wild turkeys!

Leaving leaves on grass as mulch for the winter is a great idea, but only if you have a way to break the leaves up with a mower or other method. If you don’t, they’re not likely to compost down before spring. Not cutting back any ornamentals can leave your winter garden looking sad and messy. Plant debris can build up and leave you with more work than you bargained for in spring, when you’d rather spend your time planting than cleaning.

We take a middle-of-the-road approach. We pulled up many, but not all, annuals to keep the garden from being a messy jungle and home to critters we don’t want. We left some for birds to land on or feed from. They take shelter in and eat from roses and other bushes left unpruned until early spring. And we don’t mow our grass late in the season; that’s proven to attract and feed wild turkeys, deer and elk.

Three fawns graze on grass and a pyracantha in our front yard.
Three fawns graze on grass and a pyracantha in our front yard right outside the kitchen window (which explains the mysterious reflection of my coffee cup planter).

In some areas, we cleaned up fallen leaves and used them to mulch tender perennials. But we didn’t try to rake leaves down by the river. That might help butterfly and other larvae through the winter, and if it also helps insects we don’t want, at least it’s far from the gardens.

What? More snow? Yep, as I was wrapping up this post. El Nino ...
What? More snow? Yep, as I was wrapping up this post. How about a break, El Nino?

The bottom line is that even if you can’t do much in your garden in winter, your garden and soil are doing lots for you and other living creatures. I try not to stress over whether I’m handling it perfectly, but choose and alter our approach based on what works best and what makes me feel best as I stare out the window at a blanket of white, itching to get back outside.

Another Reason to Plant Natives: No Soil Amendment Needed

Where I live in New Mexico, the soil is more alkaline than acidic. That means I might as well forget ever trying to grow blueberries, but asparagus is a great choice. We even found some old or wild stalks along our ditch bank last year.

And a soil’s pH balance is just one consideration. Soil texture and drainage are especially important to a plant’s success in a vegetable, herb or ornamental garden. If we didn’t add some organic matter to our vegetable garden each year, the soil would compact from foot traffic and lose nutrients from its work feeding plants. So each year, we work the soil with mushroom compost to keep it rich, water absorbent and well draining.

amended soil for vegetables and herbs
This is part of our ornamental garden, amended with organic matter to grow edibles this year.

Native plants

I couldn’t – and wouldn’t – rework my ornamental garden soil each year. For one, it would be nuts to dig up perennial plants! So gardeners often are advised to add a little bit of compost to the hole dug for a new tree, bush or flowering plant. The compost enriches the soil around the roots, and as long as you water as suggested in the first year or so of more rapid growth and root set, the plant should thrive. But what happens as the plant grows beyond your amendment, especially if you put in a rapidly growing shrub or tree? Eventually, the roots work their way into the soil you haven’t amended. If the soil is so poor or compacted that the roots can’t break through or thrive, the plant could be stressed at the least.

If you choose a native plant, especially for a xeric garden, it’s likely that you won’t have to amend the soil at all. A plant that is adapted to your area’s typical soil makeup will do better if you just loosen the soil around it, usually to an area at least three times larger than the root ball. No need to add anything.

chocolate flower in New Mexico rock garden
The chocolate flower (Berlandiera lyrata) is a native to our region. It crops up from seed around our garden and lawn. And yes, the blooms smell like chocolate! That’s a rosemary in the right foreground.

If plant instructions, or one article or expert tell you to add to the soil, it helps to verify the information with another source. That’s especially true if installing a native plant in your xeric garden. And it’s even truer depending on the first source of advice. There are plenty of reputable sources, and then there are myths, many of which can be perpetuated by those who stand to profit.

lavender in rocky soil
We placed several lavender plants in one of our beds, and maybe should have tested the soil first. Lavender is native to the Mediterranean, where the soil is rocky and alkaline. So it grows well here, but this soil had compacted more than we realized.That and some some cool, wet weather gave our plants a rocky start! Lesson learned.

When amending

It’s also good to check local sources when amending soil. For example, you might hear that adding sand improves drainage, but if you add too little sand, or add sand to clay soil, you can make matters worse, and your soil sets up like concrete. Oh, those poor plant roots…

Most organic matter is good for soil, but plenty of myths abound there as well. For example, manure needs to cook down or compost with brown materials before throwing it on your vegetables. Wood ash is often touted as an amendment, but not in New Mexico, where the soil already is alkaline. Wood ashes also are high in salt. I talked about Epsom salts in a previous post. The bottom line? Get local advice from a few good sources, and if you go with native xeric selections, you probably won’t have to amend the soil unless you have a severely compacted or poorly draining area.