Bought my first cactus from Lowe's ,10 in 41/2" pots and 15 in 31/2", plus a cart load of 21/2"small succulents. Made up my 2 soils ready to go. Now my new GH is starting to look like a green house.

Couple of questions.
What is the max temp cacti and succulents can with stand? my GH is hitting 115 plus and its only March, Can't put my plants outside till May. Have a 900cfm extraction fan, door and every thing open.

Do you advise using hydrogen peroxide to spray roots before repotting?

Do you advise acidifying alkaline water with vinegar?

Is there a trick to find out if your soil is dry right to the bottom of the pot? [moisture gauge]?
many thanks Bob

Chiming in here for the questions I can answer.

With pictures of your plants, we can advise about specific needs. There are quite a few succulents that cannot handle the temperatures you're talking about.

I have never used hydrogen peroxide for anything plant-related and view its rise in popularity in gardening as a fad that will fade as people realize it's not helping, and may actually be hurting, depending on the concentration.

If you acidify alkaline water (as I do) you need to check the pH afterwards. Doing one without the other is pointless, because water that's too acidic can be even worse than the alkaline water you started with. You want to dial in the amount to get the maximum benefit. I aim for pH 6.0 using a pH test kit by API that covers pH 6.0 to 7.6. Given it's at the low end of the range, I am really careful not to overshoot. For most plants pH 6-7 is ideal. The test is based on adding drops to a tube full of water and looking for a color change. I have tried pH test strips and when they work, they're great, but there's some real duds on the market.

Instead of vinegar I use a product for planted aquaria by Seachem called Acid Buffer (bisulfate is the acid), available online and in aquarium stores. A variety of acids will work, and I have seen good results by other people using vinegar. So go ahead if that's your preferred acid, just test and all is good.

I don't think the acidification is at all necessary (and our water tests at pH 9 or higher). It's a trick used by growers to shorten the time required to get a plant to size. It affects the ability of the plant to take up nutrients, basically makes the nutrients in the soil more available, but it's not like many plants will actually shut down at pH 9 or whatever. They just slow down and flower less. To decide if it's for you, find out the pH of your tap water.

I would advise against using a moisture meter until you have worked out some other way to test soil moisture. You want to know when the soil goes dry at depth, not just at the surface. If there's room, you can try poking your finger in there a couple inches. Some people like to insert a bamboo chopstick, wait a bit, then pull it out and look for a color change or wet soil stuck to it. You can judge by the weight of the plant, with some practice, pot included as long as it's a lightweight plastic type. Somebody here went so far as to weigh the pot with a scale and get an actual number to go along with wet and dry conditions. My favorite way is to carefully water a little bit at a time (waiting 5-10 minutes in between for the soil to become moist) and then look for how much water it takes to fully saturate the soil. The bigger that number, the drier the soil was before I watered.

Once you get good at working out soil moisture (experience is most of it) then you can start to use the meter as a shortcut. You need to know where on the scale (from moist to dry) the meter ends up when you know the soil is almost dry or dry, and then you can start to use that reading regularly (checking from time to time to be sure you're still on target).

Some pictures would help us a lot here.

My question back to you is: where is the thermometer located?

115F near ground level is a different kind of 115, than 115F near the roof, similarly if the thermometer is in full sun or not.

Hi Bob, That was quite a shopping trip!

with everything Baja said:

Peroxide when added to water, causes a chemical reaction that destroys organic matter. That's why its used in cleaning products (Oxygen bleach). I'm not sure why its become so popular but I hope the whole fad fades soon.

My water is pH 8.0 to 8.5. I don't acidify it. I know Baja sometimes questions my growing habits (I very rarely remember to fertilize, even though I always have good intentions and repotting sometimes takes years. ). Even so, cactus don't require much and some of mine are over 60 years old.

Does your greenhoue have roof vents? Heat rises. You don't want the heat trapped at the top, you want it to exhaust through the top. In through the sides and out through the top. A breeze is alway cooler and humidity also helps cool. You may want to think about a misting system. A shadecloth cools without blocking much light. I have shadecloth over about half my greenhouse. The succulents and some of the cactus are behind shadecloth. My greenhouse often gets to 110 but when it does, I go out and spray down the entire greenhouse, plants and all. That's with roof vents, side vents, an open door on each end, half a dozen fans, misters and shadecloth. Otherwise, my greenhouse would be a solar cooker. Your new cactus could easily become steamed vegetables. But, with a lot of ventilation, wind, humidity, and a little shade the cactus will do just fine.

Mine live in the greenhouse year round. I don't feel like moving plants back and forth and I don't have room for them outside anyway.

Yes, I would love to see what you got also.

Thank you Baja and Daisy.

Peroxide is out the window thank you both

Have ordered pH test strips 6 -7.6 range will test my well water and go from there.

My GH is 1000cu' and I have a 900cu' extraction fan at the highest point, louver vents around bottom, and with the door open 115. Shade cloth up tomorrow.

Daisy the reason I bought so many plants ,she who must be obeyed, was not with me.

My big problem now is all these Latin names, I'll be writing for ever.

About the time you get the labels done, the names will change.

can't pronounce them any way, thank goodness for pictures