The Practical Gardener

Sand box soil in need of improvement - Under layers of sand and weed barrier cloth. Compacted and receiving no organic matter (no leaf drop etc.)

So you can’t improve your soil by changing the texture (see last post), what can you do?

Well, first I need to clarify exactly what most people want from their soil – what exactly is the goal of “soil improvement”? Well, in most instances the ideal soil has the following properties:

1) Well draining – After a soil is saturated, a  certain amount of the water drains out  quickly so that there is both air and water in the soil pore spaces. Roots need both water AND air to function. Water-logged soils often lead to root rots and plant death.

2) Good water holding capacity – Ah, sounds a bit tricky to have soil that both drains well AND holds on to water well but that’s what we’re looking for.

3) Good infiltration rates – This is how quickly water enters the soil.  You don’t have to stand there with the hose turned to “slow dribble” to prevent water from running off or lose your soil to erosion as it is entrained by water during a storm.

4) Good nutrient holding abilities – Plants need nutrients, they are held in storage in the soil. You need adequate “storage” facilities.

5) Easily penetrable by roots – Okay, if you have good drainage chances are roots will also be able to move through the soil fairly easily.

If your soil is lacking one or more of these properties, you probably want to improve it. How?

Granular soil structure (good). (Picture from NASA soil science website.)

Well, I established in the last post that you can’t change a soil’s texture, but you can change a soil’s structure. Soil structure is the way in which the individual mineral grains and organic matter in the soil join together to form clumps or aggregates. You want your soil to form aggregates because you end up with a variety of pore sizes. Little pores are good at holding onto water and larger ones drain quickly providing air pockets for the roots.

Soil structure is easily destroyed and slowly built (excessive tilling, particularly when wet, and compaction are two ways to destroy soil structure). Clay soils tend to form aggregates because the clay pieces in it have a lot of – are you ready for it? – unsatisfied surface charges and they stick together like little magnets. Organic matter is also a fabulous glue. Fungal filaments, and various secretions and excretions by things living in the soil stick soil particles together.

Soil loosened with fork demonstrating massive structure (not good)

Sometimes in the top layer of soil, most of the soil aggregates are actually worm castings (worm poop). The soil passes through the worm’s gut (along with the organic material it means to eat) and everything gets altered and glued together. So keeping adequate organic matter in your soil (about 4-10%) hugely benefits soil structure and improves your soil.

Don’t just willy-nilly add piles of organics to your soil, however. (See Dr. Linda Chalker-Scott’s discussion of this.) Too much organic material can actually be bad for the soil. Get a soil test before you act. A variety of labs are available to do soil tests. I send mine to UMass Amherst because it’s cheap.

Soil had a surface layer of clay (pale) that is the remnant of former sod (mesh netting still in place). This layer will inhibit infiltration. I worked to incorporate it into the rest of the soil.

To summarize:

To improve your soil, disturb it as little as possible (minimize compaction and tilling), maintain adequate organic matter and preserve soil life – those earthworms and other soil organisms will do a lot of the work for improving your soil if you let them – so minimize herbicide/pesticide use.

Texture triangle

You often hear that adding organic matter to your soil will improve its texture. WRONG. You can’t, practically speaking, change a soil’s texture. Period. Don’t even try. more →

Low maintenance planting

IPM was developed for agriculture, where people’s livelihoods rest on the yields and appearance of what they produce.  Consequently, preventing and controlling pests, diseases and weeds that can impact the bottom line is essential.  To protect that bottom line in the least toxic, invasive and costly way possibly is how IPM decisions are made on farms.

The purpose of a home garden is different. more →

They sure aren't letting this lawn go dormant!

The key to having a green lawn with less water is to pay attention and do a little digging. more →

For some plants, the best thing you can pair it with is a wall.

Angelica sylvestris (taiwanese) ‘Vicar’s Mead’ is one of those plants. With its mahogany foliage and airy flowerheads, it can get lost in a mixed border but put it up against a wall and its dusky, sculptural beauty becomes art.

This angelica is mostly a biennial [I had one come back for a 3rd year].  It self sows, heavily close to the plant for me, but it hasn’t wandered off into the yard and become a nuisance, at least not yet. It comes true from seed. Sun-shade, reasonably drought tolerant in shade here in the Pacific NW. Simply lovely.

Is this not the most pitiful August basil you've ever seen?

Okay, it’s a bad year for basil here in Seattle – We seem to be skipping summer altogether. An article in the paper said that we have had more low clouds this summer than any other on record (since 1951) – oh joy.

One well-grown basil plant that I had kept inside from mid-May to mid-July stopped growing (essentially) and ran to flower when placed outside. All the others either stopped growing or stopped growing and went to flower.  Sigh. more →

Missoula, MT - brown hill, green trees - it's summer!

I went to graduate school in Montana. Before that, I’d never been west of Georgia where the grass grows green all summer. I still vividly remember how perplexed I was, upon arriving in Missoula in August,  to see that the grass on the hill behind the campus was brown.

“Aha,” I thought, “they recently had a fire, that must be it.”  more →

My father grew tomatoes, nothing else, just tomatoes; it’s one of my most lasting memories of him. When he lived in a condo with no sunny area, he grew them outside his office door. He grew up during the Depression, dirt poor, share-cropping in Georgia and said he never wanted to farm again but that didn’t include giving up home-grown tomatoes. more →

Photo 1 - Basil from cloche - See it hiding down there?

Oh those poor little basils that I sent out into the cold last month, how they’ve suffered. Summer only started here in Seattle on 7/6 going from coat weather to 90° heat in the space of a day. I’m not kidding about the coat weather; the kids came home from watching fireworks on the 4th wearing heavy coats with the hoods on and that is what the poor tropical basils had been out in. more →

“A ladybug can consume 50 aphids per day,” says the Ladybug Lady.  Whohoo, aphids watch out.

This assertion is supported by the folks at Cornell University.  Each day a convergent lady beetle larvae may eat its weight in aphids while an adult can take out 50.  Since this is the kind of beetle typically sold for biological control,  it sounds like our aphid problem can be solved for an investment of  $13.95 (give or take) plus shipping. Right?

Wrong. Well probably not. Here’s why. more →