Leaving my plants for 7 months. Advice needed

[Kipody]

Hey
I would appreciate your opinions and advice about a tricky situation. I have a cactus collection which I have to leave for 7 months (July-Feb in the northern hemisphere). My cactus collection includes cacti that I have for 30 years and some that I grew from seeds during the Covid pandemic. Overall I have approximately 400 plants, many of them in 2inch pots but I also have a few dozens of old plants (that have accompanied me since childhood ).
As part of my preparations for leaving I built a net house with tables and an automatic irrigation system (sprayers above the tables). My dilemma is what kind of schedule I should use for the irrigation computer. The sprayers create a very gentle drizzle, and it takes some time to saturate the pots (especially the big ones). The net house has a plastic roof so rain and hail wont make it into the net house.
I live in an area with a Mediterranean climate and the summer is hot and dry and the winter is relatively cold (it could go down to zero Celsius once or twice a year, but you also get days with 20 Celsius in the winter)
I thought of having the irrigation give the plants a good soke from July to September once every 7-10 days. During these months the max temp during noon is usually in the mid 30s Celsius (but can go up to as much as 44 Celsius in the net house on extreme days). After that I thought to play it week by week. I will be able to follow the weather forecast, and I have friends I can ask to come and reprogram my computer.
I thought that once it gets cold I would go down to irrigating once every 2-3 weeks and making the waterings shorter and trying to time them to mornings of days that are expected to be hot (asking my friends to turn the water manually and not using the computer).
I am acting on the assumption that it would be easier to kill the cacti with over watering. I am less worried about my large plants, but I am afraid that the ones in the small pots will suffer from the dry conditions during the winter.
I would appreciate any advice or suggestion
Thanks
Hagai

[Aiko]

Where in het northern hemisphere?

If you really really really get basically no or hardly a freeze during the winter, I would not bother with worrying about the cold. Basically any cactus can take up to -5C, especially if it is only occasional. The exception for a few of the known warmth lovers like Discocactus, Uebelmannia and other (Brazilian) heath loving species.

If the plants are about the size of a golf ball, I would also not worry about watering for the second part of your departure.

I would certainly open enough windows so there is always a cooling breeze, which also should limit loss of water and scorches too much. (Do you get storms that cause any open window to be blown out?)

[anttisepp]

I know cases when collection stood without any care (for sad reason) 2 years without remarcable damage.

[Steve Johnson]

First of all, it would be helpful to know where you live:

viewtopic.php?t=43816

Not sure if this helps, but it'll give you a geographical frame of reference:

Here in SoCal, our growing season usually ends in mid- to late-October. My last watering of the year is while overnight lows are still consistently in the 11-12C range. Once they go below 10C, I won't even think about watering again but with these exceptions:

• Eriosyce senilis and Tephrocactus sp. get deep watering once a month in the fall and winter. They'll live without watering, but I've found that they do better with it.

• Parodia subterranea, Echinocereus rigidissimus rubispinus, E. viridiflorus canus, and Wigginsia vorwerkiana lose their roots if they don't get occasional sips during fall and winter. By "occasional" I mean once a month, although I don't think we need to be too strict about it. Any species prone to losing their roots might be a problem for you unless you have someone who can monitor your situation. Occasional sips are fine as long as the overnight lows aren't below about 5C. FYI -- freezes in my part of LA are incredibly rare, but I'll usually get lows of 2C 3 or 4 days a year.

I am less worried about my large plants, but I am afraid that the ones in the small pots will suffer from the dry conditions during the winter.

Don't worry -- I have a small collection with a bunch of cacti in small (and a few very small) pots. While they do get all shriveled and thirsty by the end of winter, they plump up rather quickly in response to their first deep drink of the growing season. Believe it or not, I've seen a number of my cacti already plumping the day after they get watered.

[7george]

Are the plants in a greenhouse where it gets up to 50 - 60+ C during hot days?
1. I doubt that a computer can replace a human for such complicated task. Your watering timings should be the same as you were there. Quantity of water would depend on pot volume with regarding of some run off.
2. Better find a friend or a relative and give him/her instructions about watering and other tasks.
3. Large plants can do without any water if not kept in very hot conditions.
4. Be prepared to meet some (ab)normal losses when back.

[Kipody]

Thank you all for the advice. I appreciate your time and effort.

I live on a mountain in northern Israel. It gets down to -2 once every few years. Never bellow and never for more than a few hours.
It’s a net house so air does move through it. None the less, it still gets pretty hot because of the plastic roof.
It sounds as if the climate where I live is similar to that in the LA area, maybe just a bit colder.
From integrating your feedback I think that I will set my computer for significant waterings every 10 days during July-September and then ask a friend to shut it down.
After that I will follow the forecast and aim for a short spray once a month and only on days where the night temperature is expected to be high (at least above 5C)
Does that make sense?
Thanks
Hagai

[Steve Johnson]

Hi Hagai,

Just wanted to give you some additional feedback...

...I think that I will set my computer for significant waterings every 10 days during July-September and then ask a friend to shut it down.

Based on personal experience (for whatever it's worth) -- as a general rule, I would recommend significant watering every 2 weeks in the summer if you have to be on a fixed schedule. If your cacti get a bit "thirsty" between waterings, it encourages better root growth as the roots seek out water while the mix is dry.

After that I will follow the forecast and aim for a short spray once a month and only on days where the night temperature is expected to be high (at least above 5C)
Does that make sense?

Wish I could give you an easy answer on that one, but unfortunately all I can say is -- it depends on the following:

• North American vs. South American species. North American cacti (Astrophytums, Mammillarias, etc.) enjoy occasional sips in fall and winter as long as they aren't subject to temps below 5C when they get their sip. South American cacti (Copiapoas, Rebutia/Sulcorebutia sp., etc.) are incredibly rot-prone, so they need to stay completely dry during fall and winter. The exceptions are South American species that are liable to losing their roots if they don't get occasional sips. I already mentioned a few of those species, but I'm sure there are others.

• Cacti with thick taproots are also incredibly rot-prone, and they need to stay dry too -- this applies to North American species like Turbinicarpus. My Turbs get all shriveled and pruney as they go through their fall/winter dry spell -- once they get a good snootful of water to begin their growing season in spring, they're the cacti that are the first to respond with immediate plumping.

Spraying doesn't do much unless the mix gets a little bit moist (the "sip, don't soak" rule), so you'll need to determine the right amount of time it takes to get the mix a little bit moist pretty much all the way through. If you haven't made that determination yet, you can test it by filling one of your 2-inch pots with mix on its own (no plant), then find out how long it takes to get some moisture down in the pot without accidentally drenching it. One more "if"...

If your setup is sophisticated enough to have benches that get sprayed and benches that stay dry in the fall and winter, you can separate your cacti out accordingly.

[Kipody]

Hey Steve,
Thank yo for all the info.
14 day intervals will also be OK for 2 inch pots?
I understand your point thats it better to be on the drier side of things.
Thanks!
Hagai

[Steve Johnson]

14 day intervals will also be OK for 2 inch pots?

Yes -- I have cacti in pots which are smaller than that, and they get deep watering every 2 weeks in spring and summer. Believe it or not, I've found that pot size doesn't matter as much as one might imagine. There is, however, a caveat that may factor into it -- all of my cacti were well past the seedling stage when I got them, and this applies to everything I have since I started building my current collection in June 2011. With seedlings that are only 2 or 3 years old, watering every 10 days in summer may be better.

Thanks!

My pleasure!