Orchids are supposed to do best if the water is slightly on the acidic side, with a pH of about 6.5. However, they have been grown successfully in alkaline water with a pH of 7.5. Most municipal water supplies will present no problems, but there are exceptions. Water high in calcium and magnesium salts can be very hard and not lather easily so the householder often puts it through a water softener. This replaces calcium and magnesium with sodium. Sodium in large quantities is not good for orchids, which will prefer the untreated water.
Some areas have water supplies very high in solutes (dissolved substances) that may have an effect on flower growth. The only useful way of improving this water in any quantity is to put it through a reverse osmosis device in which the water is put under pressure through a membrane. This results in two lots of water: one very low in solutes and the other very high in solutes that are then discarded. These setups are fairly expensive and waste a lot of water but many growers use them. Rainwater properly collected and stored is fine for orchids. Collection from an unpainted galvanized steel roof is unsuitable due to zinc toxicity. Painted metal roofs are probably safe, but if repainting such a roof ask the paint manufacturer to confirm their product is safe for drinking water. If so, it will be safe for orchids. Water collected from the various plastic coverings used on greenhouses should be safe for flowers. Rainwater is best stored in a covered tank where it is protected from leaves and other wind-blown debris that could introduce disease organisms, particularly pythium and phytophthora. These diseases are spread to flowers by infected water.
- Watering practices
- The growth of a flower can be limited by too little water but it is not a question of the frequency of irrigation. Orchids that must be dried out between waterings must always be dried out. But when it is time to water, do it well. The logistics of watering in both home and greenhouse needs to be thought out. When it is time to water, the potting mix needs to be thoroughly wet. This may mean taking the container to a sink, so the excess water can drain, or, if watering in place, removing excess water so the flower doesn’t sit in water. The medium on the surface of the pot is not likely to show what conditions are like below. Push a finger down into it to get a better indication of whether the flower needs watering.
Epiphytes which need to dry out seem to make better growth with a short drying cycle and thus more frequent watering. If these flowers remain regularly (not occasionally) wet for as long as a week there will be a risk of root loss. The growing environment will need to be adjusted to correct this.
In the home, it can be difficult to adjust the watering regimen. The generally low humidity in the home causes the surface of the potting mix to dry out quickly, yet the generally lower light levels can mean the flower doesn’t take up as much water as would be usual.
When using a hose in a greenhouse go back in half an hour and water the same pot again and repeat this even a third time. Labor-saving overhead sprinklers can be automated and are widely used by commercial growers.
- What happens when you over-water a flower is that there will not be enough oxygen around the roots. Roots take in oxygen in order to convert the stored sugars made by photosynthesis to a usable energy form, in a process called respiration. In respiration, the oxygen taken in by roots produces carbon dioxide, which is given off by the roots. A lack of oxygen around the roots combined with carbon dioxide that can’t be carried away means root rot, which eventually means a dead plant.
Watering too often can also cause plant leaves to yellow and shrivel due to starvation because stored sugars aren’t being released. Beginners tend to panic at this sight and think that the shriveling is a sign of insufficient water, so they compound the error by pouring on more water. A look at the roots, however, will reveal rot in the form of mushy brown or black roots. Stop watering until the flower can dry out. Overwatered organic potting mixes break down much more quickly, exacerbating the problem by retaining even more water around the roots. Orchidists with a heavy hand in watering can adjust their mix to accommodate the tendency. Clay pots also help.
Watering from above the plant, such as with a hand-held watering can or overhead sprinkler, can likewise damage orchids. Water-soaked plant leaves can lead to several problems. Water standing in the crown of plants such as phalaenopsis or in the new, softer growths or leaves of many plants will cause rot. Overhead watering can also deposit calcium, magnesium, or iron residues on the foliage, reducing leaf photosynthetic ability. Direct the water to the potting mix rather than the leaves. Permanently tip forward the pots of plants that tend to collect water in the crowns, to allow water to run off. Slightly tipped is how the flower would grow in nature.
- Under-watering can result in problems too, usually less severe than those caused by over-watering. There are two kinds of under-watering. The worst is just sprinkling the top of the mix. Such watering destroys the plant’s incentive to grow deep roots since water never reaches deep enough in the pot. Likewise, because the water never drains completely through the pot, salts in the water and in fertilizer settle around the roots and cling to the mix, which is ultimately toxic. Letting water -particularly pure rainwater -drain fully and thoroughly through the pot on a monthly basis allows harmful salts to be leached out in a beneficial flushing process.
The second method of under-watering is by watering correctly (deeply and thoroughly) but not often enough. Under-watered roots shrivel, turning grey and brittle. The potting mix can be fine-tuned with the addition of more water-retentive materials. Plastic pots also aid the infrequent watering, for they hold twice as much water as clay ones will.
- Rescuing over-watered and under-watered orchids
- Over-watered plants can be rescued if the problem is discovered in time. If the mix is badly deteriorated, repot into something coarser. Plants with destroyed roots will recover better if misted and given high humidity rather than watered, regenerating new roots. If there are no viable roots left, there’s a real difficulty in saving the plant. Cut the rotted parts off and dust with sulfur. A clear, covered, plastic sweater box with moist sphagnum moss in the bottom is an excellent place to put any damaged plant for a few weeks until roots appear. Mist occasionally to maintain humidity, with the lid slightly vented, and keep out of bright sun.
Desiccated, under-watered plants with destroyed roots can be revived with similar high-humidity treatment in a clear plastic box for several weeks.
- Water temperature and timing
- Cold water, below 50°F, can damage roots, kill root hairs, and also cause cell collapse on leaves if splashed on top, particularly in warm-loving plants such as phalaenopsis. Cold roots don’t take up water and nutrients well. Use room-temperature water.
Water as early in the day as possible, to help the leaves dry and the root ball to return to ambient temperatures before the cold damp night can bring fungal and bacterial disease.
- Water quality
- In general, most tap water is fine to use to water orchids. Don’t be overly concerned about water quality unless plants seem to be languishing for no other apparent reasons. Orchids grow better when they receive water with small amounts of dissolved salts in it, such as those found in good-quality tap water, rather than distilled water. Water quality, however, does differ from place to place in chlorine, pH, mineral salts, and other solids. If dissolved salts (TDS) exceed 300, use another water source.
An excellent solution is rainwater, which normally contains very low levels of mineral salts. Many growers swear by the good results, especially for orchids particularly sensitive to salts, such as masdevallias and phragmipediums. However, using rainwater can lead to deficiencies of calcium, magnesium, and iron, even if supplemented with fertilizers, for most fertilizers don’t contain these since manufacturers assume the water supply will provide sufficient amounts. One way around this is to water with tap water every fourth watering or to mix some tap water with the rainwater.
- Softened water
- Do not use “softened” water on orchids. Standard water softeners in the home use a process that removes calcium and magnesium ions and replaces them with sodium, a salt far more toxic to plants than the original ones. If possible, tap into the water line with a “T” spout to obtain water for orchids before it enters the water softener.
If this is impractical, look into “deionizing” methods such as a “weak acid” ion-exchange resin water softener, or “reverse osmosis,” which is more water-wasting but which easily removes up to 99 percent of dissolved ions, minerals, hardness, and contaminants.
- Water pH
- Generally, the pH of water for orchid growing can range from 4.0 to 7.5, with optimum between 5.5 and 6.5, although growers have used water with pH as high as 9.0, which is very alkaline, without too much problem. A pH of 7.0 is neutral; anything below 7.0 is acidic, anything above it is alkaline.
Optimum pH increases the availability of beneficial fertilizer elements and reduces adsorption of harmful elements. Extremes of pH (below 4.0, above 7.5) can inactivate many nutrients. One reason orchids tend to withstand extremes of pH better than many houseplants is that orchids have evolved in nutrient-poor environments. Thus, even when fertilizer becomes unavailable at extreme pH, orchids survive.
Rainwater pH is generally fine for orchids. Rainwater is usually acidic, with a pH around 5.6.
If pH needs to be lowered, use citric acid (grapefruit juice works safely). Adjusting pH too much can add ions that may burn plants. Hard water, however, is difficult to adjust, since pH buffers are commonly added by municipalities.
Attention to nutrition is essential to the cultivation of good orchids. Materials incorporated in the growing medium may contain some of the elements necessary for plant growth but they contribute little until the medium starts to break down. At this point, it is usually discarded and the orchid repotted. Certain nutrients are sometimes incorporated in the medium when it is made up, but not those that dissolve on the first watering. The strength of the solution could then damage roots and be quickly washed right out. The modern practice is to put the nutrients in soluble form and much diluted in the water supply. Ideally, this should be done every watering. Little and often is the key to successful nutrition.
- A complete fertilizer mixture might have an NPK rating of, say, 20-20-20. These numbers describe the percentage of elemental nitrogen (N) and the oxides of phosphorus (P) and potassium (K).
The greatest need of a growing orchid is for nitrogen and 20-20-20 fertilizer is a good all-around one. Nitrogen requirements are highest when the plant is growing strongly under high light and lower during periods of dormancy or low light levels. Where there is difficulty in flowering, lowering the nitrogen intake often helps.
Other elements necessary for plant growth are calcium, magnesium and sulfur. Then there is a need, but in very minute quantities, for the so-called trace elements. These include boron, copper, manganese, molybdenum and zinc. Good, complete, soluble fertilizers sold for orchids should contain these in the correct proportions. Be cautious about adding them yourself as they can be toxic to the plant if applied in excess.
- Calcium deficiency is unusual but is occasionally reported in orchids. If lime was incorporated in the growing medium at the outset, calcium deficiency is probably unlikely. Municipal water supplies may contain some calcium, hard water a lot. Calcium is particularly mentioned here because commercial preparations seldom contain any at all. This is because it causes precipitates (deposits of solids) when added to concentrated liquid solutions as well as caking and other problems with dry mixes.
Calcium is a non-mobile element – the plant cannot move it from older parts of the plant to new growths if a deficiency occurs. For this reason, it ought to be available all the time. Calcium nitrate, if obtainable, can be added at the rate of about 0.02 oz per gallon or 150 milligrams per liter. If dissolved separately and added to the diluted feed solution there should be no precipitation.
- Urea is the cheapest form of nitrogen and probably, for this reason, is often included in many soluble fertilizers on the market. Plant roots cannot take in urea. In soil, it is broken down into compounds the roots can handle. In the kinds of inert media, orchids are grown in, urea may break down in a way that releases nitrites and free ammonia, both of which are not good for the roots. Urea is fine for foliar feeding. Not only can the leaves take it in safely, but urea may assist in the passage of other elements into the leaf. Most commercial preparations designed for foliar feeding are based on urea. Orchids can respond to foliar feeding but keep it very diluted and away from the roots.
- Fertilizer strength
- The NPK ratio itself does not tell you how much to use. The amount of each element in the liquid feed can be expressed in parts per million. Experiments have indicated that 100 ppm of nitrogen is about the optimum for most epiphytes and 150 ppm or more for heavy feeders such as cymbidiums. If about 0.07 oz of an NPK 20-20-20 fertilizer is dissolved in 1 gallon of water this will contain 100 ppm N, 44 ppm P and 83 ppm K. Very roughly, a level (not heaped) teaspoon is likely to be about 0.14 oz (4 g).
The strength of the feed should not be greatly exceeded any time you water. Putting 10 times the amount of fertilizer in the water every tenth watering will do more harm than good. If using a proprietary brand of liquid fertilizer, it is a little more difficult unless you know how concentrated it is. When the product is specifically designed for orchids by a reputable company it is probably safe to follow the directions given. If in doubt, use it at half the recommended strength or less.
Slow-release fertilizers are available. The most popular with orchid growers are those that have inorganic salts released over a period of time through some kind of coating. These are a time-saver but there is little control over the rate of release or when the material is exhausted. Use them sparingly and keep them on top of the medium.
- Organic versus Inorganic Fertilizer
- The basic difference between organic and inorganic fertilizers is that organic fertilizers are more complex and must be broken down by bacterial processes in order to be utilized by the plant. They are very slowly released sources of nutrients. The most popular organic fertilizer for orchids is a fish emulsion, a liquefied fish by-product with an N-P-K ratio of 5-1-1.
Inorganic sources are almost immediately available to the plant, with less lost by leaching. Nutrients from inorganic fertilizers typically show up in a plant’s system within an hour or less.
Studies routinely associate significantly smaller pest populations when organic fertilizers are used, compared with plants fertilized with highly soluble (inorganic) N-P-K materials. Plants stay healthier and better able to withstand stress. Organic fertilizers are generally more expensive, and they encourage the rapid breakdown of organic potting mixes owing to the increased microbial activity needed to break down the fertilizer. They tend to leach out of epiphytic mixes quickly.
An especially effective home-brewed organic fertilizer is made from steeping aged cow manure in water and using the diluted resulting “tea” to fertilize orchids. Put 20 tablespoons of aged 4-4-2 manure into 1 gallon of water, shake it, then allow it to sit for 24 hours. Then decant the tea from the residue at the bottom into a 5-gallon bucket, with enough water added to fill the container. Dilute this mixture further upon the use to 1:16. Teas are not robust fertilizers; they’re more like a general tonic.