Geoengineering Your Garden

Photo by YoungToymaker

When life gives you liminality, make lemons or some other subtropical (or even tropical) fruit. For us here in hardiness zone 7, climate change will probably have us in zone 8 in a decade. My palm trees and peaches will feel right at home. To grow citrus or bananas, however, a little geoengineering will be needed by way of tweaking areas of our property where the microclimate can be pushed a bit further in the warm and humid direction. In Paradise Lot, +Eric Toensmeier and +Jonathan Bates offer many suggestions on expanding your hardiness zone.

Raingardens, ponds, and swales all contribute to higher ground-level humidity. Our future hops vines, growing at a angle to a height of 35 feet should also create a quasi-greenhouse beneath, especially with the compost pit dug into the ground near their base. We also want to leverage warm, sunny spots created by South-facing walls as good areas to tropicalize.

And for that, we have a secret ingredient. Biochar, with its low reflectivity, is a great infrared energy absorber, warming the soil. It also holds about 3x its weight in water. The elevated temperature and moisture create a high humidity zone in the immediate airspace above high biochar concentrations.

My tomatoes and peppers grow prolifically, in part, due to top-dressing with biochar. Where I have cut holes in the black plastic, I mulched with biochar to prevent weeds, capture moisture, discourage pests, and further decrease albedo. I add extra organic fertilizer when it's time to feed the plants, in order to adjust for the nutrient sink created by the biochar. Next season, the biochar will be already charged and populated with soil microbes so that it can be dug in and do long-lasting service in the ground. I prefer this technique over composting of biochar, as it saves time and effort (though compost plus biochar is a superior soil amendment).

Maximizing the biochar concentration in garden beds (up to 50% of soil volume) will produce similar results. The terra preta effect will move your garden to more equatorial climes. We have a lime tree that's been container-grown for 12 years, but one day it might find its place in the sun where the snow never sticks.

Your Own Little Rainforests

Lawns do a fair job of capturing runoff, but just putting an average-sized house on a lot can double the amount of runoff from that property. Much of that increase is channeled to gutters and then downspouts, at which point an owner can take a number of further measures to reduce problems downstream. Outlets from downspouts, be they splash blocks or French drains will often evince erosion where the water is let loose to run freely on the soil. This is the place to intervene with a rain barrel and/or a swale. These may still lead to erosion wherever the water discharges, so a garden can be added to infiltrate the excess.

By concentrating the captured runoff, areas of Maryland properties typically receiving 44 inches of rainfall per year can easily get double that amount, making them like miniature rainforests.  Forest gardens are very good absorbers of groundwater, as are rain gardens.

Photo by Dion Gillard

One of my rain barrels discharges through a 25 foot garden hose into a French drain which discharges to a rock filled swale that empties into a rain garden 80 feet from the house. That easily meets the minimum distance requirement of 15 feet from the foundation and is also at a low point on the corner of my property. The rain garden contains a good deal of biochar and compost and I am planning to fill the cracks between the swale rocks with biochar once I obtain plants that grow well in rock gardens. I also have rain barrels for the other three downspouts on my home, two of which are for keeping mushroom logs watered and one for watering the five terraced garden beds in the backyard.

For water coming off an impervious surface such as a patio onto a lawn, a swale or series of them can be added that run on contour. These are interspersed with raised bed gardens that use the water captured by the swales. Yards with slopes up to 33% can use this device, so where such slopes themselves are the source of runoff, these would also be very helpful. The key to making all these alterations efficacious is gardening. To some that may create the impression of unending toil, but it needn't since the gardens will be watered by the rain flowing to them and can be kept moist and fed with the help of biochar.

Char Your Lawn

Of the nutrients that pollute the Chesapeake Bay lately, phosphorus has been the worst. "Why, of course, with all those chicken factory farms on the eastern shore," might be one's reaction to this statement. In fact, the major phosphorus inputs are coming from tributaries on the western shore of the Chesapeake. The cause has not been identified, but it could well be leaching from residential yards. Maryland soils are generally high in phosphorus, so soil disturbances by developers could also play a role.

In 2012, Maryland passed a law that prohibits the use of phosphorus on lawns except for one-time applications in cases of repairing patches, establishing a new lawn, renovating an entire lawn, or if a soil test shows a deficiency. As the phosphorus gets used up over the years, lawns will then suffer, more soil testing will be needed, and more phosphorus. Biochar can help here. Along with its many other soil enhancing benefits, biochar is very good at adsorbing phosphorus and feeding it to plants, including turfgrass. Most biochars, e.g. those made from wood, also produce a temporary liming effect in the soil, raising high acid soils' pH to one more suitable for turf (6.0 to 6.8). By applying biochar to turf, you can avoid frequent repeat applications of phosphorus and help to reduce pollution of your watershed.

Photo by Mr Thinktank (CC BY 2.0)

The steps to take when renovating a lawn include dethatching with a thatch rake or machine, and then using an aerating machine to remove small plugs throughout. After aeration, apply fertilizer-charged biochar with particle sizes small enough to drop into the newly created holes. (If phosphorus is adequate per soil test results, fertilizing with biochar will still help preserve other nutrients added, as well as the extant soil phosphorus). Spray with water to wash the char into (but not off) the lawn, then seed and water again. The biochar will also help keep the lawn moist while the seed germinates. Check the pH semi-annually to see if lime is needed and don't mow it less than 3 inches.

Permasoil

Weeds like cypress spurge can establish themselves where nutrients are scarce, but most horticultural plants require more care and feeding in order to grow to their full potential. Nitrogen is the macronutrient in highest demand by vegetables, requiring most gardeners to supplement their soils with fertilizer at certain times in a plant's lifecycle. Farmers typically use aged manure as a nitrogen source, which may put their customers at slight risk of pathogens in their produce. Synthetic fertilizers are used by most non-organic farmers and gardeners, leaving a large carbon footprint and upsetting soil microbial communities. Compost adds some nutrients, but the nitrogen is typically consumed within six weeks.

Healthy soil has the ability to cycle nitrogen to plants from the activity of microbes with no outside supplementation. Healthy soil requires the presence of live plant roots throughout the year, e.g. cover crops, with no more than three weeks dead space. If one added compost at a high rate every year, the soil could become nutrient sufficient after many decades. In the meantime, a grower needs to fertilize in addition to using compost.

The missing piece from this discussion is biochar. Biochar raises the cation exchange capacity (CEC) of soil better and more permanently than compost, meaning more nutrients will be available to plants for a longer period. If small portions of biochar are added annually to a plot of land, poor soil health can improve to a self-sustaining level in only a decade or two because it harbors a plethora of soil biota. Once soil reaches that state, it becomes a treasured renewable resource rather than a recurring receptacle. Biochar that is pre-charged with nutrients and inoculated with microbes can bring soil to a regenerative state most quickly.

Photo by Willi Heidelbach (CC BY 2.0)

You can be a successful grower by relying on synthetic fertilizers, or you can be even more successful by following organic practices, including natural fertilizers and compost, but unless you grow on prime farmland already, you can only be fully successful in your lifetime if you use biochar. Until your soil gets to that point, keep the fertilizer handy (but please hot compost the manure).

Pretty, Hardy Weed

After considering problems in critical areas, the next logical runoff concern is that from slopes in general - the steeper the slope, the greater the concern. Slopes not only erode easily, but they also often carry water away too quickly for it to infiltrate the soil. A slope of sandy soil can wash out very quickly and sandy soils are the norm here in Calvert County.

Such was the case at my church where a pocket pond filled up with sand that eroded from its banks before vegetation could stabilize the slopes. The county inspectors finally caught up to us and put us on notice to fix it. The repair plan involves filling up woven bags with the sandy deposits and stacking them on the eroded banks. In short order, we need to also establish better vegetation cover to avoid future problems. Here might be a good place to show how biochar and compost can allow things to grow in difficult conditions.

Not many plants want to grow on sandy slopes, but cypress spurge is one that I found recommended for that situation. I will be on the lookout for it on the roadside as I go about in the next few weeks. If it's as invasive as it's reputed to be, the plant should be pretty easy to find. In fact, I believe I noticed some recently, but wasn't in the market for it at the time. Though normally considered invasive, cypress spurge is the only plant for poor soil among ten recommended by the University of Maryland extension for stabilizing slopes.

Clueless Commissioners

Hugelkultur may not be in the Maryland Stormwater Design Manual, but it doesn't matter for the majority of properties. If a development activity doesn't disturb more than 5,000 square feet of land, the Manual isn't applicable. Most developed properties under private ownership are not going to build more large surfaces or structures, they just get landscaped, so we can do lots of things not discussed in the Manual that will contribute to cleaning up the watershed.

Some locations are still subject to local restrictions; critical areas, for instance. There are many homes in Southern Maryland located in critical areas, i.e. within 1,000 feet of a tidal waterbody. They are critical for the obvious reason that their proximity to the water makes them, by far, the major potential contributors to water pollution. Critical area buffers are therefore, the primary element of watershed protection that should be enforced everywhere.

Violators of critical area rules are sometimes fined when they are reported by neighbors or passersby, but there could be reinforcement of the rules by a more systematic monitoring effort to identify those who bypass the permitting process or don't follow requirements when they develop their waterfront properties. One such effort was proposed by our local Watershed Restoration Specialist that would have entailed making observations of properties via boat and reporting concerns to homeowners and authorities, if necessary. The knee-jerk rejection of said proposal by a St. Mary's County commissioner elicited the rejoinder,"Why Mr. Commissioner? What are you doing illegal on your property?"

Clueless in Tarcoles by Carol Blyberg  (CC BY-NC 2.0)

I hope someone does finger that particular politician and that he ends up paying in full for whatever he is trying to hide. Meanwhile, in Calvert County, Evan Slaughenhoupt, has raised the ire of environmentally conscious citizens by his favoring of Dominion with their white elephant LNG plant construction. He also seems to favor opening the gates wider in the county to land development, with all of the lovely environmental consequences, one of which is the failing D grade given to the Patuxent River on the latest Chesapeake Bay Report Card.

Charcoalkultur

Infiltration berms belong at the public works level, but a comparable practice for us masses is hugelkultur. I attended a talk last year at the Mother Earth News fair comparing biochar to hugelkultur and discovered that hugelkultur is generally easier and less chancy than making and applying biochar. Yet, a hugelkultur bed will not be as long-lived as one with a load of biochar.

Hugelkultur is the practice of piling soil and organic material on top of a bunch of logs and sticks to form a mound (mainly on contour) which can capture runoff in order to grow plants like a super high raised bed. +paul wheaton published a DVD about it and  +Sepp Holzer put some good instructions on Paul's richsoil website.

I've been using hugelkultur to augment swales in order to reduce erosion on the back slope of my property. My previous post about infiltration berms brought me to consider hugelkultur not as an alternative to biochar, but as another opportunity to put biochar to good use. Filling the gaps with biochar (or some percentage thereof) while building a hugelkultur bed is one way. Biochar could also be applied in areas where there is a need for extra moisture.

Such was the case with my wife's hydrangea which she wanted planted in a sloped area that normally would not stay moist enough for this plant. Yet, there is a roof downspout nearby which spills out onto the slope (via a splash plate) once the rain barrel fills up. I built a quasi-hugelkultur bed to direct the overflow to the hydrangea and loaded the outlet with unground biochar in order to slow the flow of water and hold it close to the plant.

There is enough of a dam behind the biochar to keep it from being washed away. Over time the biochar will break down into small particles and leach into the soil where it can do even more good.

I can see using biochar in a similar fashion on the uphill toe of a hugelkultur bed in order to reduce the tendency of the toe to erode where runoff sheetflow meets the mound. For highly steep slopes (> 25%), a deep swale on the uphill side of the hugelkultur mound containing some percentage of biochar could serve the same purpose.

Swales are an approved ESD practice in the Maryland Stormwater Manual. Hugelkultur beds aren't, but there may be enough latitude in the specs and descriptions that it would fit without requesting special approval. Beyond these practices, terracing is the next step for reducing runoff on steep slopes. For that, heavy equipment is needed, so it's better in most cases to think in terms of swales and mounds.