Reducing Water Usage

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There are various ways that we can reduce the quantity of water needed to keep our orchids alive and healthy. In the Canberra region the low humidity in summer and current water restrictions means we must strive to get the greatest benefit from each drop of water.

The following are a few ideas that you may wish to consider, especially for use in the warmer weather. You may already be using these ideas while some may not be suitable or practical depending on your circumstances. Also be aware that changing your current practices may raise new problems and challenges.

1. Use mixes that are more water absorbent/retentive.

Especially effective in this regard is coarse coir (coconut). Coarse coir is easily wetted and allows good air circulation. While the fine particled coir peat is good at holding water, on its own it is generally too dense to allow adequate air movement around the orchid roots resulting in rotting of the roots. A mix that is quite suitable is perlite and peat moss (about 8 parts perlite, 1 part peat moss). Some growers have added water crystals to bark based mixes, but this is not popular. If using the coarse coir take note whether it includes fertiliser and adjust your fertiliser program accordingly. Also the coarse coir includes a lot of fine material - consider screening out this material for certain orchid types such as angraecums.

If you have orchids in coarse bark, consider increasing the water holding/wetting of the mix. Try adding some diatomite chunks (these wet well and help to prevent the bark from getting too dry or to rewet bark that has become water-repellent) or sprinkle some dry coco peat over the top of the pot, then tap the side to get it to sink lower into the mix. You might need to modify you watering regime in the cold weather so as not to get the mix too wet.

2. Make alterations to the growing environment to reduce the rate of evaporation (and thus the amount of watering required).

If you have a shadehouse, try enclosing some of it, at least the bottom metre, with agricultural plastic in order to reduce evaporation loss. You can cover the entire house, but then would need to allow adequate ventilation and ideally evaporative cooling as the enclosed air temperature will get to 10C or more higher than the outside air if in full sunlight.

If the lower part of the shadehouse is enclosed, humidity will be higher and temperature lower on the floor of the shadehouse. Some orchids, particularly the terrestrial types such as various sarcochilus will be happy there. However, if the light level on the floor of the shadehouse is very low, some orchid species may grow too rank and flowering will be reduced.

A layer of plastic on the floor of the shade/glass house covered with some porous or water absorbing material will help raise the humidity and lower the temperature. Try using wood shavings, pine chips, scoria, old carpet, or even concrete blocks (especially the hollow ones). Ideally the material should not compact too much, so that some air circulation through the material and release of moisture is possible.

Consider covering your benches with water holding material (eg coco peat on top of shadecloth). This will capture any excess water and help raise the humidity. Orchid roots may however grow through the bottom of the pot into this material.

If you are growing orchids in an unenclosed structure or under trees, place them close together. If watering with a hose, water is more likely to get to the plants and there will be less evaporation loss. Cymbidiums (hybrids) in particular can be placed as close together as the pots will allow until spikes are emerging. Do not put small and large plants too close together as the small plants may be covered and deprived of light or not get sufficient water. Be careful putting plants close together in a glasshouse, as this may accentuate wilt and other disease problems.

3. Get the maximum use from water.

If you have a small number of orchids and have the time, the most efficient method of watering is to dunk 'em. Dunking ensures that the entire potting mix is wetted which may not always happen in other watering methods apart from flooding. The following diagram illustrates one such approach. It is suggested that you have three buckets (used 10 litre paint/glue buckets are fine). Use the first bucket as your source of water and add fertiliser if appropriate. Tip a suitable amount of this mixture into a second bucket into which you will place the potted orchid. Top up the water level so that it will just reach the pseudobulbs. If the pot is very dry, it will initially float so you may need to push the pot into the water. Leave for a suitable time - a couple of minutes if the mix is coir, half an hour or more if mix is coarse bark and it is very dry. Lift the orchid up, wait until water stops flowing freely from the pot (a few seconds) then place in a third bucket in which a squat plastic pot has been inverted, and allow to drain fully. At the same time the process can be started for a second orchid. Water collected in the third bucket can be reused (tip into the second bucket). Check your orchids carefully - it is important that diseased plants not go though the same water as healthy plants.

Dunking is also very effective for orchids which are on mounts or rafts.

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If you don't want to dunk, try holding the pot over a bucket and pour water over the pot until sufficiently wet. Retrieve water from the bucket for the next pot.

Capture excess water.

If using a hose, you might consider making a system for capturing any water which drips through or misses the pots. For example plastic sheeting can be fixed under the benches to make troughs. Provide a slope so that water will flow to one end for easy collection. Again, do not reuse any water from diseased plants. Use rafts in preference to mounts. A raft refers to any solid material which is positioned horizontally. This gives greater opportunity for water to be absorbed.

Suggestions provided by Bill Ferris

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