There’s one piece of equipment which stands out as a clear winner when it comes to growing beautiful, healthy and robust carnivorous plants. It’s not good quality stock or pots with lots of drainage holes. It’s not top quality media either. All those things are definitely important. But today I am talking about a TDS meter. In my opinion they are the most underrated and underutilized tool in the carnivorous plant growers arsenal. If you’re serious about the long term health of your carnivorous plants, I can’t suggest investing in a TDS meter strongly enough. This one piece of equipment can prevent absolute disaster if used properly.
TDS meters are used to test water purity. They indicate the total dissolved solids (TDS) of a solution. Dissolved ionized solids, such as salts and minerals, increase the electrical conductivity (EC) of a solution. EC can be used to calculate TDS. TDS is measured in parts per million (PPM). The greater the TDS PPM reading of water the less it’s suitable for carnivorous plants.
A safe long term TDS reading for carnivorous plant water is 50 parts per million (PPM) or less. By itself that doesn’t mean much so let’s put that measurement in perspective. Sea water is 30,000 – 40,000 PPM TDS. Fresh drinking water is up to 1,000 PPM TDS. Our tap water in Mount Compass fluctuates a bit, but generally averages 80 PPM TDS. Some growers say a TDS of less than 100 PPM is fine. Personally, in our nursery, we don’t use water with a TDS measurement greater than 10 PPM.
We based our decision of 10 PPM TDS on the TDS of clean rain water. Captured rain water has a TDS reading in the region of 5-50 PPM (depending on whether it is the first rain of the season, mid winter or at the end of a good rain storm). Rainwater does fluctuate greatly in terms of TDS, especially when collecting rain water of roofs and structures which collect contaminants during summer. As the rain washes down a roof and gutters it collects salts and nutrients which can quickly make the water unsuitable for carnivorous plants.
Using a TDS meter is very easy. Collect a sample of water (around 250ml will do) in a clean container. Turn on the TDS meter and insert the contacts into the water. Dont let the contacts touch the bottom of the container. Keep your TDS meter in the water until the reading on the LCD screen has stabilised, normally takes ten to fifteen seconds.
Test water going into pots and trays and also coming out of pots and trays. This way you can get an idea of salt and nutrient content of your media too. Without a TDS meter you are flying blind. You might be headed for disaster with no way of knowing until it’s too late. We test our trays once a week to make sure the water is within our acceptable range. We also test our product water from our Reverse Osmosis (RO) units frequently so we know when to change filters.
Every six to twelve months you need to calibrate your TDS meter. Calibration solutions are available to keep your TDS meter accurate. These solutions have a very accurate known TDS. The TDS meter can be tuned to match the calibration solution if it reports a discrepancy.
The TDS meter shown below is the unit we use in our nursery. This unit costs between $25 – $45 depending on where you buy. Most hydroponic supply shops sell TDS meters. If you have trouble finding a TDS meter please get in touch. We are more than happy to recommend a few suppliers.
This particular TDS meter can also measure water temperature in °C. TDS readings are displayed as PPM. The other handy feature of this unit is the hold button. Pressing HOLD stops the reading disappearing when you remove the contacts from the water. This unit will also turn itself off automatically to save battery power if you accidently leave it on. On the topic of battery power, the battery life is fantastic. Used at least weekly, our units last years without a battery change.
To care for your unit always wash the contacts with water (ideally distilled water) and return the lid after you’re finished testing.