Most every gardener thinks about things like the condition of their soil, whether/when to mulch and what to use, what kind of fertilizer is best for what they grow, and myriad other questions that have to do with supporting their gardens so that they flourish. Luckily we have lots of experts in our midst here in the Portland gardening community, and one of those folks is Heather Havens of Concentrates Inc. If you’re not familiar with them already, Concentrates is a supplier of agricultural products specializing in organic soil amendments, fertilizers, feeds, minerals, and salts.

Concentrates’ staff members include organic farming and ranching professionals with degrees in Agriculture, Horticulture, Chemistry, and Resource Management. They are available to answer any questions you may have concerning your organic crop and livestock needs, including soil test interpretation, balancing feed rations, organic pest management, cover crop rotations, troubleshooting livestock health issues, vegetable planting schedules, home orchard maintenance, irrigation system design, season extension, and more.

They’re located in Milwaukie, OR, and conveniently right near Bob’s Red Mill, so you can make a trip out there to not only stock up for your garden, but also for the baking season ahead!  I asked Heather a few questions that frequently come up with gardeners…

Q: What do you think about using fallen leaves as a mulch?

I’m a big fan of using fallen leaves as fall & winter mulch, but there are few things I keep in mind when using leaf mulch:

When you are ready to plant again in that area, unless those leaves are completely composted by then, move them aside before working that garden soil, don’t mix them into the soil, as they will be a Nitrogen sink (will rob the soil of Nitrogen, as the plant material decomposes), rather than a soil nutrient.

• Don’t use leaves from a tree that has allelopathic leaves, like black walnut.
• Don’t heap them on TOO thick, especially easy to do if they are already wet, as they will clump and prevent good aeration of the soil.
• Don’t let them touch the base of trees or shrubs.
• Shred them with your lawnmower if you can, although I rarely have had that opportunity.
• Don’t use leaves that come from piles left on people’s curbs, they will have pollutants from gasoline engine exhaust, tire & brake dust, oil, etc…

Q: How do you know what kind of soil you have in your garden?

I very strongly recommend getting a soil test done, as most people over-apply and misapply fertilizers when they don’t get soil tests done. We recommend getting A & L Lab’s test done, and particularly their “Full Graphical Analysis with Recommendations”, for about $36 plus postage, or about $47 if we mail it in for you. Their website also gives excellent instructions for collecting your soil samples. Concentrates is happy to help interpret the results from A & L Lab. I also recommend getting tests done in late summer or in fall, while the soil is still warm, your soil has long since been amended, crop production is about done, and the rains haven’t started yet. It is a great way to get a preview of your soil’s condition in the following Spring, and in the Spring the soil is cold, heavy, and wet, so soil test results aren’t as accurate, and labs are very busy.

Q: What’s a good bacteria or fungi vs a bad one? What does a vibrant and flourishing microbial community in your soil do for your garden?

Beneficial soil microbes are the workhorses of a vibrant garden. These microbes actually digest and process the natural soil amendments and fertilizers that we add to our gardens, and break these products down into plant-available nutrients, which are in forms that your plants can take as they need them. Beneficial soil microbes, and healthy plants, will also help fend off pathogenic soil microbes if they are present.

Q: Is fertilizer necessary to use in a garden? When do you use it? Why is organic fertilizer better than synthetic?

You may or may not need fertilizer. If you are growing natives, or established perennials, you may not need to amend at all. If you are growing this type of plant, and they look good, they probably are good!

If you plan to grow food crops, or annuals, or want a plant to be a heavy producer, you will probably need to fertilize, and the best way to know what you need, is by doing a good soil test (see above). When I do fertilize, I normally add some good plant based compost (as a soil conditioner and soil microbe inoculant), the correct fertilizer/soil amendments for the situation, lime if the pH needs to be raised, and gypsum if clay soil is a problem, or if Ca or S are needed, but the pH doesn’t need to be adjusted.

I prefer Organic or Natural soil amendments over synthetic ones, because when soil microbes and natural soil amendments work together, they create plant nutrients that plants can take up as they need them, vs synthetic fertilizer that essentially force-feed plants, and are often more nutrients than the plant needs, and can salinate the soil and pollute the environment and groundwater. Natural fertilization also promotes healthy, sustainable, growth, rather than growth that is too fast, leading to other problems.

Another caution against synthetic fertilizers is this: They can cause a flush of growth that literally “pumps & heats up” the plants, and insects can see this, and this attracts them to an easy meal! Not good!

Q: What are the benefits of mulching your garden? When should you do it & what’s best to use?

Healthy mulching keeps down weeds, preserves moisture, keeps roots cool, and prevents damage from the cold. Incorrect or over-mulching can cause problems, however, so don’t over-mulch, and never allow mulch to be in contact with the crown, stalk, or trunk of trees or shrubs. Any time you want to prevent weeds, protect seeds, keep soil cool, or prevent damage from cold, mulching is a good idea!

Ideally, a mulch is coarse and non-nutritious enough that weed seeds will not germinate on it (this is why compost is not really an ideal mulch, seeds love to germinate on, in, and under it). I like a mulch that is coarse, and also easy to move aside if I want to plant or seed, and move back once the plant is planted or germinated. I find straw too full of seeds which become weeds, and difficult to work with once it is all soggy and moldy. I do like alfalfa hay or “chaffehaye” (fermented alfalfa hay, comes in a nice big plastic bale), but they can be expensive for mulch. I also like wood chips (free with getchipdrop.com) or bark mulch (uncolored & untreated), because seeds don’t like to germinate on these, and they are easy to move aside, then move back, or set aside until later. I also like rice hulls, as they aren’t very coarse, but they are very non-nutritious, and are OK to work into the soil.

Ideal mulches are very carbon and fiber/cellulose rich, which means they take a long time to break down. This means they are NOT good to incorporate into your soil, because they will take a very long time to break down there, creating a “nitrogen-sink”, sucking nitrogen from your soil system to make decomposition happen, making your plants very malnourished and unhappy. So, DO NOT mix wood chips or bark dust into your soil if you plan to grow anything there any time soon!

Q: What amendments will help our gardens be more resilient to climate changes?

First, grow plants that will do well in the climate that is coming, in the places you plan to grow them. After that, add organic matter as needed, by adding good plant-based compost (manure is not the same as compost), cover cropping (entire books are written about this), or adding worm castings. Organic matter inoculates your soil with beneficial microbes, and gives these microbes places to live. Organic matter is a source of long term, slow release nitrogen, the plant’s most used nutrient. Organic matter retains moisture in your soil, “buffers” it (makes incorrectly fertilizing more forgiving), and keeps it cooler. Organic matter, and the corresponding microbes and soil organisms, add porosity to the soil, keeping it properly aerated and drained, and allowing for root penetration. Top dress with compost yearly in most circumstances, and work in if you are planting (never more than half compost to half native soil).

Q: What are some ways we can help our gardens be more resilient in the winter so that they bounce back quickly in the spring?

“Put your gardens to bed” before winter. Remove (or sheet mulch, or cut short) weeds (make sure to remove any weed seed heads especially!), and “done” annuals. Add (top dress or lightly till) slow release soil amendments like compost, rock dusts, and lime and/or gypsum. Plant or seed as appropriate. Then mulch for the winter. Once Spring comes, you can move aside the mulch, add fertilizers made from plant or animal meals if needed (seed meals, feather meals, bone meal, etc…, need determined by soil testing) and start gardening once the soil dries out enough (never work wet soils, you will create compaction and destroy healthy soil structure).

Many thanks for Heather for this wealth of knowledge!