Water and Drainage

Water is essential to plant growth, and both lack and excess of water are of great concern to the grower. While the requirements of individual species vary tremendously, and for many plants are detailed in the species database, general principles will be discussed in this document.

Drainage

While plants often recover readily from some degree of drought, overwatering is very frequently the death of a prized plant. The gardener may not be at fault: poor soil conditions, bad weather, and/or a high water table can create environments that will not support most species.

An excess of water deprives a plant's roots of oxygen. As such, even most water-loving plants will prefer loose, well-drained soil, where ideally both moisture and oxygen are readily available. This principle is key to hydroponic gardening, but useful also in problem-solving ordinary gardens.

Waterlogged soil is also cold, and inhibits growth in spring; fungal disease does better in cold, damp soil. Well-draining soil is not created instantly, though well within reach of the determined.

Compost (yet again), manure, straw, peat, as well as coarse sand, will all improve poor-draining soils. These should be dug or tilled in, as deep as is possible. Gently mounding the surface of this area helps shed water, and tends to keep people off, and thus prevent soil compaction. Especially if developing a new area of soil: do it right the first time.

Raised Beds can locally vastly improve drainage, even in areas of heavy clay; see the separate section on this topic. Alternatively, the technique of double digging, while working in large amounts of nice, light compost, can create very well-drained areas within your garden.

If spring melts and local run-off contribute to waterlogging, then gently sloping the land in desired directions may be helpful. Open ditches are most effective at carrying away surplus water, but may be cosmetically unacceptable. However, any form of gravel-filled drainage ditch will work well. The drainage tile or pipe is surrounded by coarse gravel, and both ditch and tile should angle downward.

One such form, the French drain, consists of a layer of coarse sand over the actual drainage ditch, upside down sod layered over this, and covered with topsoil, and works almost as well as an open ditch.

Drainage ditches must be laid judiciously to be effective, to not create new problems elsewhere. If in doubt about where and how to install a drain-age system, contact a local landscaper for advice.

Double digging

Double digging is a method of deeply working the soil, and is ideal for creating raised beds, or normal beds of very well-drained soil in areas where drainage is a problem. It involves removing the topsoil, cultivating the subsoil, and returning the worked topsoil to its original location; as such, it's an arduous process best done over several days, and only once. A loose, very well-draining soil results, and the resulting bed need in future years only be worked lightly with hoe and fork before planting.

The process is simple: starting at one end of the bed, remove the soil from a trench some 12-24" wide and the depth of the spade, setting this aside in a dump cart or on tarp spread onto the ground. Next, dig the subsoil at the base of this trench, again to the depth of your spade, very thoroughly until nice and loose, and rocks have been removed.

Move over and dig a second trench along the first, loosening the soil well as you remove it, and tossing rocks aside. Deposit this well-worked top-soil onto the worked subsoil of the first trench, filling it in completely; the soil will naturally mound to some degree. Next, work the subsoil of the second trench as before. Then start a third trench and continue this process, using its topsoil to fill trench number two, etc., until the other end of the bed has been reached.

When finished - again, double digging takes plenty of time and effort - fill the final trench with the topsoil removed and set aside when the first trench was dug. Limit yourself to creating only one or two beds a year in this fashion.

Using Water/Irrigation

While all plants require water, some are far more drought-tolerant than others. Still, most garden varieties require a regular supply of abundant water. Water takes time to penetrate soil, and if administed as a large amount, even over a few hours, directly to a flat soil surface, most will be lost. Water slowly and thoroughly, not too often, rather than frequently and shallowly.

Soil is important: well-draining soil will allow water to be absorbed effectively, to penetrate down to the roots, as well as allowing oxygen to reach the roots, thus encouraging larger and healthier root systems. Soil rich in organic matter will also retain moisture well, and mulching can help trap moisture further.

Creating a small trough around individual plants forms a simple way of reliably administering water, eliminates runoff and ensures that water soaks down to where it's needed.

A very old but efficient delivery system consists of good-sized clay pots planted into well-dug and compost-rich soil, which are then filled with water. Water slowly oozes through the sides into the adjacent soil, and can provide water for several days to a week. Standard flowerpots work well for pitcher irrigation, but should have the bottom drainage hole sealed off; covering the top of the pot prevents evaporative losses. Note, however, that pots will break in areas of significant frost.

Sprinklers are inefficient: much is lost to wind and evaporation, and the amount reaching different areas varies tremendously. Still, they are inexpensive, can cover large areas, and are quite suitable for lawns, if used in moderation. Note however that over-reliance on sprinklers leads to plants with very shallow root systems, and lawns less healthy and resilient than many that are neglected, and sometimes dry and brown in summer.

Soaker hoses are a marked improvement on sprinklers, and far cheaper than drip irrigation, though less easy to regulate. It's ideal for vegetable beds, borders, anyplace plants are found in rows. Water is readily aborbed, little is wasted. Still, while good on flat ground, soaker hoses do not distribute water evenly on slopes, and algae can build up in the hoses and become a problem especially with untreated well water.

Drip irrigation slowly delivers small amounts of water, at carefully regulated rates, directly to the soil surface, and is efficiently absorbed. Plant yields increase while water losses to evaporation are virtually zero. Better systems compensate for slope, and deliver the same amount of water at each emitter.

A good drip irrigation system consists of shutoff valve, an antisiphon valve and filter, pressure regulator, valves for each drip line, a timer, the hose, emitters (sometimes just holes in the hose) and optionally emitter tubing. Avoid most 'kits' unless these are based on industry-standard parts. These systems are very effective, if expensive, and often not portable.