Water in the Garden: Too Much or Too Little

June 1, 2023

By Will Bonsall

Water is essential to every biological process, so successful gardening depends on enough water being available at the right time. It may be in the soil or even in the plant tissues themselves, but it must be present and available. Without it you can load the soil with endless nutrients and they will be quite useless if not actually harmful. Plants can only assimilate nutrients that are in an aqueous solution: a reminder that it all started in the primordial sea.

Therefore, providing adequate water is a central concern, but what about too much water? For one thing, plants also need air (including oxygen), and while some air is dissolved in the water itself, waterlogged soil becomes anaerobic (air deficient) and intolerable for plant rootlets. Moreover, excessive water dissolved in the air (read “humidity”) is conducive to disease, especially fungal infections.

Water 1
One of several 400-gallon tanks that hold water from a 150-foot well and gravity-feed it to wherever it is needed on Will Bonsall’s farm. Courtesy of Sandy Tiner

Too much water, too little water, too much air, not enough air, too warm, too cold. How are we to manage all these Goldilocks conditions to make things “just right”? Fortunately, we mostly don’t need to. Garden plants can tolerate a certain range of imbalances; indeed, they make some corrections on their own. After all, those plants evolved without our being around to tweak everything for them. However, there are some things we can do to temper the extremes and assist garden plants in doing their own thing.

Whenever natural rainfall is inadequate — increasingly common in these changing times — we must bring water to the plants, i.e., irrigate. I use a combination of leaky hoses and drip tape. I used to have a strong bias against using all that black plastic (which is made out of ticky-tacky and doesn’t grow on my farm), especially when I was given to believe it had to be replaced every year. Then my cousin, Tom Vigue, pointed out that some of his drip tape has been used for 15 years with careful handling (he even designed a clever device for rolling it up every fall for storage indoors). Now I have used plastic ballpoint pens that don’t last a year, even with refills, so I consider drip tape a much more reasonable compromise, along with the 400-gallon recycled plastic tanks that I combine to make a gravity-feed storage system. I greatly prefer drip tape to overhead sprinklers, which waste much water through evaporation (plus they splatter dirt on foliage). By covering my tape with mulch (mostly shredded leaves), the water gets delivered gently and precisely, and is better retained.

For some soils, especially heavy clays, it may be necessary to remove excess water by ditching. I’ve developed a few styles of ditches for different situations. A simple dug ditch, created either with a spade or plow, will often suffice to remove waterlogged surface soils, but it is a constant obstruction for mowing, tilling or just getting around. Moreover, the rim of the ditch will eventually sod over, a good thing to prevent constant refilling of the ditch, but that’s a new edge or border strip to harbor witchgrass and other invasive weeds. Sometimes I’ve wanted a deeper ditch than I wish to work around, say a couple of feet deep. It is usually needed to allow standing or subsurface water to slowly seep away rather than carrying actual flowing water. I may fill that ditch with stones, larger on the bottom for more interstices, and smaller near the surface to minimize loose dirt sifting in and clogging the drain over time. By filling the ditch to the brim, I can continue to move equipment (wheelbarrows, etc.) around without obstruction. In a few cases, such as under a roadway, I’ve dug the ditch extra deep (2-3 feet) and instead of merely dumping in stones I’ve shaped a channel by laying two rows of stones (the walls) and capped it with larger flatter stones for a roof before filling the rest of the way as described previously. This elaborate extreme is only necessary where the ditch is carrying flowing water as opposed to mere seepage. Of course, one could simply use PVC pipe for that channel, but that doesn’t grow on my land whereas rocks do, and abundantly.

Of course, whether one needs such ditches at all depends a lot on the natural soil texture. In very light sandy soils, the question is moot; indeed, it’s a question of too much drainage, which I’ll discuss soon. Heavy clay soils are quite a different problem and not just because water tends to collect and stay too long, but in the meantime the soil tends to be anaerobic, sometimes developing a “garbagey” smell. Of course, one can add lots of sand to clay soils for greater porosity, and one can a work in lots of clay into sandy soils for better retention (of water and nutrients); however, that can be pretty extreme, given the huge quantities needed to make a real difference. For less severe situations there’s a simpler solution, which is a remedy for extremes of every kind. I’m speaking of course of the hallmark of every organic system: humus. High humus levels serve as a buffer for many soil problems. Too acidic? Too alkaline? Too wet? Too dry? Some mineral imbalance? Bring on the humus. By absorbing excess moisture and retaining it until needed, humus moderates all these problems to a high degree.

When we speak of humus, most people think immediately of compost derived from animal manures. While those may be helpful, they’re far from adequate. Animal manure is so high in nitrogen and phosphorus that in order to add enough humus to effect water stabilization, you will necessarily be adding an excess of those nutrients, creating a soil imbalance while polluting the ground water. To profoundly impact the soil texture (of either clay or sandy soils) we need to add longer-lasting organic matter, materials which are richer in carbon, especially cellulose, and thus more absorbent. (See my article on ramial wood, “Too Many Wood Chips,” in the winter 2018-2019 issue of The Maine Organic Farmer & Gardener.)

Ramial wood, or chipped brushwood, will take much longer to decay than, say, a cowpie, and thus will allow a much greater buildup of organic residue without creating imbalances. And since water is what we’re talking about here, such high-carbon residues will absorb vastly more water than animal wastes and release it over a much longer time — we’re looking at a 10-15 year effect from a single application. During that long span, the humus is not so much a material as a community, largely composed of lifeforms living and dying and giving rise to new life, which incidentally includes your crop plants. Like all the other building blocks, water will be constantly sequestered and released, buffering any extremes.

Lastly, there’s another form of excess water: that which is dissolved in the air as humidity. When excessive it can encourage the growth of plant pathogens, especially fungal maladies. Of course, humidity is largely a function of the weather, and we can’t do much to effect the weather, but we can do something to avoid air stagnation. We can space crop plants at appropriate distances for good air circulation, perhaps orienting the rows to the prevailing winds. Crowding plants for greater yields may make sense up to a point, but if the gain is offset by losses to diseases, then what’s the point?

Will Bonsall lives in Industry, Maine, where he directs Scatterseed Project, a seed-saving enterprise. He is the author of “Will Bonsall’s Essential Guide to Radical Self-Reliant Gardening” (Chelsea Green, 2015). And indeed, he is also a distant cousin of another exemplary Maine horticulturist: Tom Vigue. You can contact Will at [email protected].

This article was published in the summer 2023 issue of The Maine Organic Farmer & Gardener, MOFGA’s quarterly publication.

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