Using Water Efficiently; from Ollas to Huglekultures to Lithic Mulch

We live in a high plains desert, where water is a problem. Denver only gets fifteen inches of precipitation in an average year, and much of this evaporates without infiltrating deeply, or comes as snow in the winter. On the other hand, in many years there is too much rain in the early spring, and summer thunderstorms can drop an inch of rain in a few hours, causing disastrous flash floods. In this post I will focus on how to cope with too little water; many of these strategies work both ways. I’m not going to discuss rainwater harvesting or greywater; both are very interesting and promising techniques, but are outside the scope of this post. There are lots of complicated details in regard to each; hopefully I will be able to give each of them a separate post in the near future.

Our focus is on using water wisely to grow annual vegetables and edible perennials, not ornamental gardens.

Also, I’m only giving a brief summary for each of the techniques below. As we implement them on the farms this summer, I will write a more in depth post on each with photos of our work.

Drip-line/ Soaker hose

These are a much more efficient way of using water then spray irrigation, because they don’t wet the leaves and soil surface. This also helps to prevent fungal disease. However, they are expensive, and tend to wear out over time. They are easy to damage with gardening tools. Also, they only work with clean, high pressure water, so they can’t accept rainwater or greywater.

Ollas/ Bucket Irrigation

Ollas are an ancient irrigation method. Small clay jugs or pots are buried near plants and filled with water. Depending on the moisture level in the soil, more or less water seeps out. Clay pots can be pricey. A cheaper alternative is a five gallon bucket with a small hole drilled in the bottom. Water will slowly dribble into the soil, soaking in deeply without wetting a large surface area. Buckets could be moved around to different beds, unlike ollas, which are immovable, but they lack the sensitivity to soil conditions gained with porous ollas. Delis and bakeries are good sources for free food grade buckets.

Wicking Beds and Containers

Wicking beds contain a subsurface reservoir of water, generally formed by a layer of gravel, which slowly wicks up through the soil to the plant roots. They eliminate surface evaporation and nutrient leaching, and keep the soil evenly moist, avoiding under and over watering. This is very important for some plants, such as tomatoes and lettuce. They are labor intensive and expensive to build. A cheaper variation is a wicking container built on the same principle. They can also be built from 5 gallon buckets.

Dew Catchment

This is the least tested of the ideas on this list. The basic principle of dew catchment is to insulate a smooth reflective surface, thus isolating it from ground heat at night. This lowers its temperature because of radiant cooling to the night sky. Once the temperature of the surface falls to the dew point, condensation collects and is funneled into a container or directly into the ground. Dew catchers can also improve the utilization of light rains, turning a surface dampening shower into a ground soaking drip of water on one spot. If you have any experience with dew catchment in Denver, let me know!

Mulch

Organic mulch is a double edged sword from a water utilization standpoint. A thick layer of wood chips, leaves, straw, or other organic matter can retain moisture in the ground, and works well in combination with ollas, bucket irrigation, drip lines, and soaker irrigation. However, mulch can soak up a surprising amount of spray irrigation or rainfall before any reaches the ground. Since roots usually don’t grow in the mulch layer, this water is wicked away and evaporated into the air. However, when correctly applied, mulch can go a long way towards drought proofing a garden and has many other benefits.

Lithic Mulch

Native Americans in the southwest used rocks as mulch in their gardens, which held moisture in the soil, and also increased the infiltration of light rains by shedding water rapidly into the soil. They may also capture moisture from warm air condensing on the cool lower rocks during the day. However, they can overheat plants and complicate the management of the garden. (For some plants, the extra heat is an added benefit.) In the wild, plants seem to grow lushly in and around talus piles at the base of cliffs.

Soil Management

Raising the organic matter percentage in the soil increases the amount of water that can be stored for dry times. A foot of rich soil can hold three inches of water. Also, deeply loosening soil can increase rooting depth and water infiltration. Double digging can achieve this on small sites, and chisel plowing on big ones. Hugelkultures, which are buried mounds of woody debris, achieve both these objectives. In this climate, sunken hguelkultures are probably better then the mounded types seen elsewhere. Mini hugelkultures can be dug into the ground for individual plants. Soil can also be contoured to catch water running down slopes and retain irrigation water, but this is a complex topic for another article.

Plant Spacing

Plant spacing can work both ways. A dense, Biointensive style planting can be lightly irrigated to create a moist microclimate under the leaves, slowing evaporation and speeding growth. However, wide spacing of large plants gives each plant access to more water, since the plant will react by growing a larger root system in the larger soil volume available per plant. In the end it depends on the objective. If one has a lot of room and hardly any water, then wide spacing is probably best. If one has only a little room and wants to use their available water to best effect, tight spacing will do well.

Fertilization

All else being equal, a plant in a fertile soil can get by with less water then one in an infertile soil. In a fertile soil with all the minerals in balance, a plant has to absorb and transpire less water to obtain its needed nutrients. This does not always apply, and fertilizer should not be overused. Also, woody plants should not be fertilized when they are water stressed.

Pruning

How a plant is pruned makes a big difference in how much water it uses. This is a very complex topic, and I would advise you to do your own research.

Transplants

A flat of transplants can be placed in the shade and watered more efficiently then the same seeds planted out in the eventual bed. This also has the effect of expanding the size of a small garden, since a bed can continue growing crops while the new transplants get going. On the other hand, some plants such as squash can sustain damage to the root system when they are transplanted, which reduces their ability to search for water. Large seeds should be pre sprouted until the root tip is just emerging, then planted. This helps conserve water and avoids root damage.

Timing

If plants can be started a few weeks earlier, when there is still abundant water available, things will be much easier later on. Cold frames, row covers and transplants are all valuable here. Also, deep waterings once a week are much better then shallow ones daily.

Variety

Some varieties are better at searching for water then others, and some types of vegetables are simply more drought resistant. For instance, purslane grows wild here in the summer with very little water, whereas lettuce is always thirsty and wilts in the heat. All else being equal, older varieties are more likely to be breed for tolerable performance in sub optimal conditions, but this is not always the case.

Windbreak/ Shading

For plants that tolerate the shade, an over story crop or shade structure that blocks the wind and direct sun can make a huge difference in the amount of evaporation losses.

Capillary Connection

Soil that is too loose can keep water from moving upwards through the soil. If necessary, the ground should be firmed around new transplants and seeds.

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Breeding “Landrace” vegetables

Our eventual goal is to save all the seeds needed by our farms, for several reasons. It will lower our expenses, and allow us to adapt varieties to our own climate, soil, and growing preferences. It will free us from dependence on the corporate world, and help conserve the world’s threatened genetic diversity. However, the standard methods of maintaining heirloom or open pollinated varieties are difficult and time consuming. (If you are not sure what heirlooms, hybrids, etc. are, please see my last post.) To get around this, we will be raising landrace crops. Before I explain landraces, here is what is entailed in conventional seed saving.

To maintain an open pollinated variety, two dangers must be avoided; cross pollination, and inbreeding. Cross pollination occurs when plants from different varieties in the same species share pollen. Inbreeding occurs when seed is saved from too few plants in one generation.

To prevent cross pollination, plants of a given variety must be isolated from other plants in the same species. The distance necessary to do this varies. Corn pollen blows for miles on the wind, and squash plants can be crossed by bees with other plants miles away. Tomatoes, on the other hand, can be isolated by about ten feet or so. Also, plants that seem very different are sometimes in the same species, and can cross pollinate. Cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi and most kales are all in the same species. Pumpkins, some winter squash, zucchini, summer squash and many gourds are also all in the same species as one another. So for some plants, isolation is difficult or impossible, especially in the city. Hand pollination, with cages or bags to exclude unwanted pollen, is possible but time consuming and difficult.

The need to prevent inbreeding further complicates this issue. Some plants will not suffer any damage even if seed is saved from one plant. But some, such as corn, have a minimum population size of a hundred plants. This makes hand pollination even more difficult.

And for most vegetables, it is best to grow several varieties. This hedges a gardener’s bets against the weather. It also makes a garden more interesting. But it certainly makes conventional seed saving even more difficult.

However, there is a way to avoid all this work, and gain some additional benefits. One can abandon the idea of saving pure varieties and save landraces. Most traditional societies saved landraces, not pure varieties. A landrace is a locally adapted population of plants, which is more diverse then a pure variety. Fruit size and color, pest and weather resistance, and days to maturity may vary from plant to plant. This provides the community of gardeners with insurance against bad weather and other problems. The genetics of the landrace slowly change over the years; new mutations or gene introductions persist if they have value in the local area, or fade away if they do not.

To start a modern landrace, many open pollinated or hybrid varieties are planted together and the seeds saved from each plant. If neighbor’s gardens contribute pollen, that is a benefit, not a problem. Then, each year seed is saved from any plant that does well enough to produce seed. (If only the highest yielding plants were selected, genetics that might be valuable in a year with different conditions would be eliminated.) Over time, genetics that yield no benefit to a given area will be eliminated. If one wishes, separate land races can be created for different traits; for instance, an early tomato landrace and a main season landrace, or landraces based on different colors of produce. A small amount of crossing between these landraces will not be detrimental so long as one selects for the desired trait every year. And a landrace can be as diverse (or not) as one wishes.

This approach gives several benefits.

  • Maintaining a landrace is far easier than maintaining five or six varieties of a given vegetable.
  • A landrace will adapt to a given set of conditions, whereas a bunch of pure varieties will stay much the same. Just because a plant is an heirloom does not mean it will do well in any  garden; much more likely it means that it does well only in one particular area of the country.
  • Landraces will also adapt to a given set of cultural practices. If seeds are planted early year after year, there will be a natural selection for fast emergence in cool soils. If plants are left un-staked, sturdier plants will have the advantage. Similarly, if the best tasting plants are selected, a particular gardeners landrace will reflect that gardener’s tastes.
  • Landraces are interesting; a wide diversity of fruit types can be produced, since the genetics are recombined each year.
  • Landraces are unique. Nobody else will be growing the exact same landrace. And the individual plants may be different than any heirloom or commercial variety out there.
  • With some species, the natural hybrid vigor produced by this method can generate more vigorous plants.
  • For those so inclined, landraces can be used to generate new pure varieties. If a particularly good plant shows up through the constant rolling of the genetic dice, it can be stabilized to produce a new open pollinated variety.
  • The wide range of maturity dates in a landrace can be useful. For instance, most home gardeners don’t want to deal with 50 broccoli heads all at once. On the other hand, this can be one of the small drawbacks of landraces; some gardeners may want uniform harvest dates.
  • For those worried about genetic diversity or food security, landraces make it easier to preserve genetics and produce food, even in difficult climates. In fact, landraces really shine in marginal climates. Most seeds are grown and varieties bred for mild, wet climates, and will not perform optimally in high, dry, cold, or harsh climates.
  • Landraces give gardeners control. All plant breeding reflects the values and ideas of a particular plant breeder or institution. Landraces make it easy for a gardener to become a plant breeder, so that their plants reflect their goals and values.

Of course, standard seed saving practices still have much value. I’m very thankful that seed savers have worked to preserve our heritage, the thousands of diverse varieties passed down from previous generations. We will still isolate some varieties, particularly pepo summer squash to avoid pumpkin genetics, and some tomatoes to generate more varieties for sale. But landraces will make it far easier for us to become self sufficient in seed and maintain high genetic diversity.

Eventually, we hope to start a landrace seed bank in the local area, so that gardeners can work together to maintain and trade a large pool of Denver adapted landraces, with our farms providing the space for larger grow-outs.

For more information on landrace vegetable breeding, check out the Home Grown Goodness forums. There are a lot of folks there who are working on landrace projects. Of course, I don’t agree with everything said on that forum about this or any other topic, but by and large it is a community of friendly and knowledgeable people. I have learned a lot from them.