We delve deeper into the whys of a poor garlic crop this year, and although I highly suspect it was a combination of a long wet winter and spring, incessant strong winds, and too thick a mulch, I thought it might be a good idea to buy an NPK soil-test kit and see what the soil could tell me.
First, About My Garden and Soil
I have six 25-ft-square (more or less) plots around which I rotate the garlic. The first plot, however, I have decided to reserve for the family veggies, and I might turn the 2nd into a berry garden – but that still leaves a 4-year rotation for the future. When it comes to garlic, rotation is important in preventing diseases.
Last fall, I turned under a green-manure crop of crimson clover and also purchased 3 yards of very good plant-based compost for the plot (thank you Lazy J Tree Farm!), which I spread around in September. I built four 4-foot-wide beds the length of the plot and added lime, bone meal, and some raked maple leaves to the beds during the process.
I thought I would have the best crop ever this year. The soil seemed almost fluffy in the beds. Throughout the year, I was able to pull out long (very long!) dandelion roots with my bare hands. Weeds were rather prolific along the sides of the beds. I let them grow through much of the winter to help hold the beds in place, but in the spring, I whacked them all back and turned them into compost.
However – and this is a big however – in digging up the garlic plants (keep in mind, all watering had been cut off for a good 2 or 3 weeks prior), the soil did not seem “fluffy” at all to me. In fact, quite the opposite. Which was extremely disappointing, because I had been working green manures into this plot for several years now. And despite the dry streak, some areas seemed almost cold and damp.
So Now for the Test
I took only 2 samples to start with, a few inches down beneath the surface, as directed on the package.
Back at the house, I donned my lab coat and safety glasses. Ahm. As an aside, I used to work alongside chemists at a national lab (actually, I did administrative and marketing work, but our offices were next to each other, so I gained an appreciation for chemistry by close association), and I learned that one of the key things when taking samples for analysis is not to contaminate your own sample. This seems like a no-brainer, but is surprisingly easy to do. Well, let me just say to all my chemist friends out there that I totally disregarded “ultra-clean” techniques (Sorry. Have I learned nothing?). I got my bare hands right in the dirt and mixed it all around. I used spoons right out of my silverware drawer. I breathed all over everything. I used water right from our well. This is just a little home-test kit, after all. Jeesh. But if I really wanted to know exactly what was in my soil, I’d be more careful and send it to a lab where they would do it right.
Ok. So what do my tests tell me.
According to the ATTRA National Sustainable Agriculture bulletin, a pH of 6.8 – 7.2 is ideal for garlic. Our soils usually benefit with a light dusting of lime, which I apply every year on the garlic beds. The pH reading looks about right. This is good. Fungi and molds like a low pH. Healthy microbial populations cannot survive in extreme pH ranges. pH also affects availability of phosphorous and other nutrients. pH is not the problem. (whew)
In the spring, the garlic is a starving leafy plant and requires a lot of nitrogen to do its photosynthesis miracle. Bigger plants make bigger bulbs (yes, size matters, relatively speaking). Also, vigorous plants are more resistant to disease. Microorganisms play a strong role in converting organic nitrogen to an inorganic form that plants can use. Heavy soils with a high clay content, however (which I am always battling), have a tendency to make nitrogen unavailable. When the garlic starts making a bulb, its nutritive needs shift accordingly; if you have too much nitro at this point, the bulbs will suffer.
I usually plant green manures in the off seasons, incorporate compost into the soil at planting time, and use a light side dressing of blood meal in the spring, along with foliar sprays of fish fertilizer and worm tea. Adequate? Maybe not.
My nitrogen reading is on the “depleted” end of the scale. This was a surprise to me. Unfortunately, I have no idea what the N levels were in early spring. I am leery of nitrogen when it comes to garlic. One year I topped everything with about an inch or so of well-composted and washed dairy manure, and I had a similar harvest to this year’s: lots of mold, neck rot, and insect damage. I was not sure whether it was too much nitrogen or whether the mulch kept everything warm and moist, ideal conditions for critters and fungi. Probably a combination of both. (That said, I am still a believer in the dairy compost and had approx. 7 yds of it dumped on the plot for next year – so we shall see how it goes! Thank you Dungeness Valley Creamery!)
I have already started my fall veggie garden where the garlic was. This low N reading tells me I better feed the broccoli. Soon.
Phosphorous is needed for roots, stems, and fruit – which is just about everything. A symbiotic relationship with mycorrhizal fungi assists this process. However, even though phosphorous is often abundant in soils, it is not always in an available form to plants. Clay soils (like mine) tend to bind the P. Plus, phosphorous is easily eroded in rains.
My P reading is somewhere between sufficient to surplus. Even though my P levels are high, I don’t think it negatively affected the plants. I usually add bone meal to the soil before planting, and I am going to keep doing that based on the advice of old-time farmers in my area who have been at this a lot longer than I have.
K: Potassium / potash
Potassium is needed for flowering and fruiting and helps plants resist disease. I think of potassium like the plant’s thyroid – it controls metabolism, helps them function, converts food into energy, controls water uptake, etc. Like phosphorous, though, it is difficult for the plant to get adequate amounts because it is either leached out in sandy soils or bound to particles in clay soils. Availability is also reduced by low moisture, low temperatures, or low root growth. Plants low in K have low root growth (you can see the cycle here), weak stems, and the outer edges of older leaves may appear burned from lack of water.
My K readings are, again, between sufficient and surplus (it’s kind of hard to match up the colors on these things, but it’s definitely more dark than light). If lack of K is a problem, I would guess it would be because it is not available. My main sources of potassium are grass clippings, alfalfa meal, and kelp. Some years I have added a little greensand to plots with particularly stubborn clay streaks, but I have read that greensand, although a good soil amendment, releases potassium so slowly that is not a good way to add K. Next year, I might take a soil reading midseason before adding more K supplements.
The Rest of the Story
The NPK readings tell us one part of the story. Amount of organic matter, minerals, and micronutrients tell another. I highly suspect these latter are the key to good garlic, but it seems like a roulette game to start throwing a bunch of single-sided amendments onto the beds and hope they work themselves out in the season. I make a growth booster that is a combination of seed meal, lime, bone meal, and kelp, as recommended by Steve Solomon in “Growing Vegetables West of the Cascades.” I have added alfalfa meal, but it makes more sense to me to just grow and turn under alfalfa. It is easy to go overboard on this stuff, and at a per-box price, the $$ quickly add up. It’s kind of like vitamins: if you eat a variety of whole foods, you have a better chance of getting what you need in balance. In the end, I am a strong believer in good ol’ compost, fish fertilizer, and worm teas, although I never seem to have enough compost.
Test my soil both before planting and after harvesting (i.e., before planting something else in its place) and maybe again midseason
Keep adding organic matter to the soil – as much and as often as I can – to build a lighter soil with balanced nutrients and one that supports microbial populations. Good soil structure is key to good garlic.
Keep records of what I do.
International Plant Nutrition Institute: http://www.ipni.net/ – “The mission of IPNI is to develop and promote scientific information about the responsible management of plant nutrition for the benefit of the human family.” International focus; lots of useful information.
Growing Vegetables West of the Cascades: The Complete Guide to Organic Gardening – written by the founder of Territorial Seeds, this book contains a wealth of information about soil and how to build it. I refer to it for all my gardening questions, including garlic.
The Complete Book of Garlic: A Guide for Gardeners, Growers, and Serious Cooks – I have not read this book, but I did browse through it for quite awhile at my local feed store. It is definitely on my “next to buy” list. When they say “complete,” they really mean “complete.” It’s the best I’ve seen yet on the subject of garlic.