CactiGuide.com

I'm thinking about getting a moisture meter so I can better judge when my plants should to be watered. I potted my plants with several different soils, and moved them outside recently, where the drying is not as consistent as inside, so I've just been guessing when they need to be watered. But I wanted to see what other people's experiences were first. Do these things really work? Does a cheap one work as well as an expensive one? Other advice?

I think they work better in normal open ground plant soils than ours for potted cacti. The cheap ones seem to rely on being plunged to a certain depth and some moisture being there to work because normal plant soils are never let to dry out completely between watering's, as cactus soils are. Apart from the largest pots I find you cannot stick the probe in far enough for a satisfactory reading, but that may simply be the cheap moisture meter I was using which has no batteries and works simply on galvanic action like these:-

https://www.ebay.co.uk/sch/i.html?_osac ... s&_sacat=0

The professional £200+ ($269+) ones may be more accurate, but I have never used one.

I find the same is true with the cheap PH meters which seem to be less accurate than even cheaper PH testing strips off EBAY. I bought one which consistently showed the rainwater in my rainwater butt as alkaline, where the cheap PH strips showed it was slightly acid as you would expect. I guess you always get what you pay for.

DaveW wrote: ↑Sat May 19, 2018 11:59 am I bought one which consistently showed the rainwater in my rainwater butt as alkaline, where the cheap PH strips showed it was slightly acid as you would expect.

Did you calibrate it with a buffer solution?

I've got a cheap moisture meter that I picked up from a garden centre much like the one in the link (mainly for my other houseplants rather than the cacti and succulents). I've found it doesn't always work so well in mixes with lots of inorganic matter (grit/gravel etc.) - always reads it to be drier that it actually is! (It works perfectly to check the moisture in my bonsai tree's pot and my venus fly trap pots because they are mostly organic growing medium).

I use wooden labels (ice lolly sticks usually!) for my pots and find that if I take that out and its totally dry, then that seems to be the right time to water my desert cacti (in my growing conditions). I've found its better to wait a week to water rather than risk overwatering. I've killed a few plants by overwatering now (I'm getting better at not killing them though!) I do have to replace the labels after a while (usually a year or 2) but it seems to be a great way to find out the moisture levels in my pots!

The problem with that type of meter is it depends on the electrical contact of the probe with the potting mix, which will vary with different kinds of mixes (as stephanelli discovered). I have one somewhere, I don't use it any more.

Yes I did calibrate the other one with buffer solution Ellie. It was strange, it gave correct readings for my tap water, but not for the rainwater in my water butts when I checked these using cheap indicator strips off EBAY. Unless it is one of the more expensive models I would not bother with one as test strips work just as well.

https://www.ebay.co.uk/sch/i.html?_from ... s&_sacat=0

My uncle was an engineer and they were having trouble with cooling water in a steel mill. They had a firm along with all the top of the range PH testing equipment and found the PH of the water was satisfactory, but the problem still persisted so my uncle went to the local chemist and bought some litmus test strips and found the water was in fact acidic. Red faces all around with the PH testing firm as it was their expensive machine that was at fault. Sometimes the simplest methods can be the best and often just as accurate, if not more so on occasion.

As Spence says those cheap moisture meters depend on galvanic action and need to be in contact with the moisture to work. Gritty soils may still be damp but the probe is not really in good contact with the moisture to register this. They work far better in normal type silty or humus soils.

Good to know, thanks