Tips for growing plants in pots in an arid climate

I used to live in a townhouse and had no garden space that wasn’t covered over, so I tried growing some plants in pots.

That . . . didn’t work very well. Everything had to be heavily watered once a day, preferably twice, and that just wasn’t sustainable. So everything died.

I’ve been experimenting with pots again since moving to this house, and I’ve discovered a few things. Maybe these will help anyone who wants to grow a garden in pots in a place where the humidity is nonexistent and the summer heat is high.

Discovery #1: Pot color.
Black pots will cook your plants if the sun goes above 90 degrees F and the pots are in full sun. Roots don’t generally want to be 100+ degrees F. If all you have are black pots, you can alleviate this issue by burying the pots at least halfway down into the ground, or by painting the pots white, or by surrounding them with something white (a white cardboard box, maybe). If you can make (or buy) light-colored pots, try those.

Discovery #2: Pot materials.
Do nooooooooot use clay pots. Or fabric grow bags. Or cardboard. (Which can make quite nice pots in wet climates. Please note that it needs to be brown cardboard only with all tape, labels, and glossy sides removed.) Those dry out significantly faster than plastic. If you’re in a very wet climate, that’s a good thing. If you’re in an arid climate, the plants will probably die. If you don’t want to use plastic, try something that doesn’t let moisture escape from the sides easily, like glass, glazed ceramic, wood, or metal.

Discovery #3: Consider the season.
In my climate – zone 7b with averagely wet winters – pots are great in the winter, so they’re a convenient way to stratify seeds. Conceivably a winter garden could also be grown in them, as long as you remember that the roots will get colder at night than if they were in the ground. In winter here, pots can be left in full sun and mostly ignored.

Discovery #4: Make the drainage holes smaller.
Most purchased pots, including the ones that come with plants from a nursery, have very large drainage holes. In an arid climate, you don’t want that! You want to have a teensy weensy amount of drainage, no more than absolutely necessary to let excess water leach out the bottom to prevent root rot. You can decrease the amount of drainage either by blocking some of the holes that are there, or by making your own pots and only making teensy scissor nicks or needle pinpricks on the bottom.

Discovery #5: Turn the lower half into a sponge.
Make the bottom half of the pot very good at absorbing water and very reluctant to let it drain out. I generally do this by sticking several layers of cardboard on the bottom, filling the rest of the bottom half of the pot with wood chips, and filling the top half with native soil. You don’t need to purchase potting soil, and in fact, you don’t want to. It’s much too well-draining. And it’s not particularly eco friendly.

Discovery #6: Stick kitchen scraps in the bottom, too.
Especially if you’re filling the bottom with carboard, paper, autumn leaves, wood chips, etc., it’s going to be full of carbonaceous materials. Stick some nitrogen in there to keep the carbon company and turn it into rich, fluffy compost. Kitchen scraps are great. (Be aware that if you add anything with seeds, you will probably get volunteers.) Diaper fluff from the interior of wet diapers is even better, because it also adds free water crystals and paper pulp that will compost rapidly. If you do this, not only will the plants need less water, they’ll also need no fertilizer.

Discovery #7: Mulch.
You definitely need to have half an inch to an inch of mulch on top of the soil in the pot. Small wood chips work. So do leaves or grass clippings or shreds of paper or cardboard. Just don’t stick weed seeds in there accidentally, if you can help it.

Discovery #8: Capture the drainage water.
Either have some kind of tight-fitting saucer underneath to capture the drainage water and wick it back up to the pot later, or put the pot next to a plant in the ground that you wouldn’t mind watering. A fruit tree, for example. Don’t use a tray underneath with a lot of surface area exposed to the sun. If you do, all drained water will evaporate.

Discovery #9: Use very large pots.
The bigger, the better. A quart is not big enough. A gallon is not big enough. A ten gallon pot may be big enough. A twenty gallon pot or bigger is probably safer. Remember: the larger the pot, the smaller the surface area exposed to the sun, thus the less water will evaporate from it per hour. So the bigger the pot, the better.

Discovery #10: The pots still can’t be in full sun.
They just can’t. Not in zero humidity and summer heat above 90 degrees. Well, they can, if you really want to water them every single day, but do you really want to see everything die if you forget to water it one time? Give them no more than four hours of full sun per day. If you live in an area with very intense sunlight, like I do, that will be enough for most “full sun” crops to thrive.

After a lot of trial and error, I’m doing all of those things with some plants right now, which means I can usually get away with watering them only once a week.

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Oh, an addendum:

All of my large pots (twenty gallons or larger) are black, so I have to keep them in almost full shade. If the pots were the same size but white, I could probably get away with keeping them in mostly sun.

Burying black pots into the ground does help a great deal, so if all you have is black pots and you have the option to at least partially bury them, that may be worth a try.

Buried pots can be useful for plants that you don’t want to spread, like mint, or for plants with edible bulbs (like grape hyacinth) that you want to eat that look exactly like the poisonous bulbs of a common weed in your area (like star of Bethlehem).

So pots can be useful for many reasons.

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Great tips! I’ve done a lot of this.
I usually use a small layer of mulch or leaves in the bottom to slow drainage. I do buy potting soil but usually stretch it with compost, because my clay soil would be terrible in pots.

You can also cut the bottom out of a pot being buried and just use the outer ring to prevent spreading plants. I did this with a large pot for a bamboo and it worked very well.

Grape hyacinth is edible?! :exploding_head:

Yep, both the bulbs and the flowers! (Not the stems or the leaves, or at least so I’ve read.) The flowers taste like grapes with a very bitter aftertaste, so I’m not enthused. But the bulbs are apparently a traditional Italian delicacy!

They have to be cooked, otherwise they’re poisonous. But they’re supposed to be fine after cooking. I’m pretty interested in giving that a try, but I would have to be absolutely, 100% sure I’m using grape hyancinth bulbs, not star of Bethlehem, so I figure a pot of grape hyacinth that I could definitely identify while they were flowering (and make sure there were no stars of Bethlehem mixed in there) would be the safe way to go.

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Yeah, clay soil probably wouldn’t be ideal in pots. Unless of course you bought a bag of pure sand (probably cheaper than potting soil), and mixed it with the clay? That may give you some cheap loam to play with.

You would think that would work but mixing clay and sand actually makes a very compacted substance.
The small particles of the clay fill in the space between the large sand particles.
It is actually a recipe for creating certain types of brick.

The best solution is almost always compost/organic matter!

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Whoa, I didn’t realize that! It seems like it ought to work, but not if it bakes into bricks. (Laugh.)

We have good success with straight compost (homemade from garden cleanings and vegetable scraps or from our regional waste management composter - we’re planning a formal trial to compare the two) in containers, and both of those options are free to us. It does settle a fair amount, especially the first year, but we just top off every season (and sometimes mid-season for tomatoes in a new container). When it gets to the point of not having room to add an inch of new compost to the top after 5 years or so, remove some for a refresh.
I think perfect might be to add 10 percent clay to compost, but that’s not locally viable.

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Anytime I end up with some extra clay from digging or planting I toss it in the compost.

I’ve accidentally started a lot of plants that grew straight from the compost pile. Some stuff just loves compost. The only time I really mix potting soil is for things that are picky or require extra drainage like cacti/succulent type plants.

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I have Emily’s next YouTube channel based on that post.

For anyone who doubt’s the clay-ness of Justin’s local clay, I used to live in the same geological formation. It’s the mother of all clays.
I now live in a giant sediment bed that benefits from all the organic matter it can get for other reasons.

I have almost exclusively switched to compost-pile special winter squashes. I just make sure the squash guts from the squashes that have mediocre flavor go to the industrial composter, so I can accidentally grow good tasting squashes.

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Ha ha ha, I love that approach! Makes perfect sense to work with the way the plants want to grow, rather than trying to make them fit your ideal preferences.

@peterd That does look like a worthwhile YouTube channel! I’ll have to check it out. :slight_smile:

The terrace in my flat is a dryer: sun the whole day, constant winds from east and west, and heat, not so much as in deserts, but more on the warm side. Even if I can water my pots, they are really difficult to keep moist (especially the potting soil).
Even so, I’ve managed to grow a few things, doing things similar to you.

My tips.
#1 Shading and wind protection. No matter how much a plant loves to be under the sun, there’s no way it can survive in a pot under such conditions. Having many plants together gives them shading and wind protection from at least one side. I have some oleanders and small olive trees to provide shade for the more tender ones.

#2 All pots must have a pot tray under them. If the substrate ever dries out, there’s no way to hydratate it again unless it sits on a tray. The pots have to be watered until there’s water overflowing the tray for salt dilution.

#3 Clay pots are ok but they consume more water. On the other hand they keep the roots cooler if there’s moisture left. To make up for the extra water consumption, use a larger tray.

#4 Plants do not like to be close to the wall, it’s hotter. I guess they would not care so much if the wall wasn’t exposed to the sun the whole day.

#5 I have some special pots made from milk plastic bottles, with a water reservoir about 2 inches high, that I can separate from the pot. Ideally, I’d water the pot until there’s overflow, then I would not irrigate again until the reservoir is dry (and hopefully the pot is still a little moist), but I always forget to follow my advice. These keep the plants moist, but I need to check periodically whether the reservoir smells putrid. I haven’t yet solved how to prevent salt concentration (legumes die really fast).

#6 Oh, watering with rainwater really makes a difference in salt concentration and pH. I guess desalinated water can do, but my machine broke a few years ago and I haven’t replaced it.

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All good tips! Thank you!

I was talking to my husband about the fact that we seem to have much harsher sun here than in most places. I said that I’ve noticed even drought-tolerant plants that want “full sun” seem to want partial shade here.

He said, “Yeah, we don’t have clouds.”

Oh! Duh!

I’d say at least half of our summer days have absolutely clear skies, and most of the rest have only a few wisps of clouds.

So, yeah! That’s why even squashes and tomatoes do much better with some filtered shade. Because they need leaves above them to take the place of the clouds that aren’t there!

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Exactly.
“Full sun” is misleading. Our UV index is over 8 most of the time.
Another misleading advice is the recomended month for seeding, good for temperate climates, not for the rest. I think that could be better if they were noted in fenological time.

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Even within temperate climates the planting month(s) can be highly inaccurate.

Good point about the recommended months for seeding. Do you find advice like “two weeks before the last frost date” is usually useful in non-temperate climates?

I looked up “fenological time,” but I’m not sure I grok it. Can you give me some examples of what that would be?

I think @AbrahamPalma means using phenological cues to determine when to sow seeds. When forsythia blooms, it means the soil temperature is warm enough to sow peas, for example.

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Thank you! Yes, that would make sense. :blush: