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Garden success in a heat wave: 3 key tips

Scorching forecast:

  • There is a heat wave forecasted for next week.
  • Therefore, I wanted to provide some tips and insight on how to successfully prepare your garden for a heat wave.
Hot sun

Hot sun


The hot problem for any plant:

  • Unseasonably hot weather may catch your plants off guard.
  • If they are not adequately acclimated, the extreme high temps can cause all kinds of bad things such as leaf scorch, leaf droop, fruit drop, stunting and even plant death.
  • Yes, even hearty succulents and cactus can be damaged by extreme hot weather if they are not ready for it.
Even desert southern Africa native lithops genus can be burned when shade is abruptly removed on a hot dry day

Even desert southern Africa native lithops genus can be burned when shade is abruptly removed on a hot dry day


Plants most at risk:

  • The newly planted and young are the most vulnerable to heat stress.  Part of this has to do with the fact that these plants don’t have the matured root system needed to keep up with extreme water evaporation from the leaves.
  • In addition, plants of any age that are infested with parasites such as aphids are at additional risk.  This is because the parasites are also literally sapping additional fluids out of the plant.  Furthermore, these parasites will be sucking even more than usual during the hot days because those bugs will also be trying to hydrate themselves in the hot weather.
Citrus branch shows  permanent damage to leaves from water stress on a hot dry day

Citrus branch shows permanent damage to leaves from water stress on a hot dry day



What to do?

  • There are three major things that you can do to decrease the negative impact of a heat wave… and even come out ahead.
  • Below is my heat wave checklist.


1. Over water your plants.

  • When the forecast warns of a heat wave, I increase the settings on my automatic irrigation system.  However, for the plants at additional risk, such as the newly planted, I will also go out with a garden hose and give them an extra soak.
  • The most efficient time of day to water your plants is in the very early morning.  This will allow the water to soak down deep without excessive loss of water through surface evaporation. You could also water in the early evening.  However, the drawback of that nighttime approach is that prolonged nocturnal moisture can promote fungal growth.
  • Regardless of when you water, a key factor is to plan ahead of the heat.  Meaning… you should water your plants before you see signs of heat/water stress such as wilting leaves.  Another words, if you water on the wrong side of the equation, it may be too late for the health of your plant.  There is a tipping point for a water stressed plant, and if that point is passed, an unavoidable cascade of negative events will follow.
  • On the up side, high temps can also stimulate growth.  Therefore, if you can successfully keep up with the water demands of your plants during a heat wave, your plants may reward you with a new flush.  I have found this to be particularly true with citrus.

Extra watering for young and recently planted plants


2. Shade the young ones:

  • The combination of extreme dehydrating heat and sun can burn leaves and branches. These effects can be curtailed if you can keep up with the water needs (see section above).  However, sometimes water by itself is not sufficient to avoid damage.
  • The ones most vulnerable to this type of damage are young seedlings, plants that are acclimatized to shade and the thin bark of recently pruned trees.

Therefore, if you have young seedlings in pots, put them in the shade.  If your young ones are already in the ground, then move some things around to give them shade where they are planted.  There are even cool shade tunnels made specifically to protect young  plants from the sun.

For the older plants, avoid pruning leaves and branches in the summer. This will help to protect the unaccustomed branches/trunk from getting burned.  However, if you have recently pruned your tree, or if you plants have particularly sun- sensitive branches (like fig trees), then there are other options.  One of the most direct approaches is to coat susceptible exposed branches and trunks with white latex paint.  See my earlier post on Mission Fig tree cultivation for additional info.

I recently espalier trained this Mission Fig and then whitewashed the bark to to protect it from the sun

A recently espalier trained Mission Fig tree. The bark was whitewashed to to protect it from the sun


3. Kill those weeds:

  • This is perhaps my favorite part of a heat wave. Those weeds in your garden are going to be exposed to the same heat stress as your cherished plants.  Unfortunately, those darn weds seem to have an unnatural resistance to extreme weather.  That weedy advantage can quickly be turned around with a simple organic spray.


How to kill weeds organically:

  • Spraying weeds with a mix of vinegar and some soap will disrupt their ability to regulate water evaporation.  Therefore, after being sprayed with this mix, they basically dehydrate to death. This technique will work anytime, but it is most effective during very hot-dry weather.
  • See my earlier article on “Awesome organic weed killer” for more specific details.
organic weed killer

What you need for organic weed control


Be safe:

  • Hot weather should be respected by all.
  • Avoid working out in the extreme heat if you can.
  • If you have to be out in it, plan to work in the early morning or late evening.
  • And keep hydrated.

A group of feeding vultures.
Photocredit: en.wikipedia.org/wiki/Vulture








About Thomas Osborne, MD

Dr. Osborne is a Harvard trained Radiologist and Neuroradiologist who loves to share his insight about medicine and gardening.


  1. I have a two yr old meyer lemon.lots of fruit, but they dont want to turn yellow? I live in Deltona Florida. Trees are in pots. What should I do?

    • Thomas Osborne, MD

      Hey Kelly
      Great question.

      There are a bunch of reasons why a lemon may not be turning yellow.

      Growing conditions:
      All citrus trees need lots of sun, moist soil and fertilizer.
      Too little of any of these components can result in a small crop or fruit that doesn’t ripen correctly.
      The appearance of the leaves may be a good indicator of the plants health (for example; yellow leaves is bad sign). If you are not sure about the health of your tree then send me a link of some pics and I will try to help figure it out.
      All citrus need micronutrients, but potted citrus are even more susceptible to micronutrient deficiencies.
      This is a nice organic option Sea-90 100% Organic Fertilizer — Reconditions soil by replacing the essential minerals & trace elements gardens, flowers, orchids, and citrus plants need. Water Soluble. Sea 90 is great for Hydroponics & is the perfect container plant food. Money Back Guarantee.

      Infected Tree:
      An infected tree may divert its energy into fighting the disease and pay less attention to the fruit.
      Check for aphids, ants, etc.
      Those little suckers like to hide under the leaves and at the angles/joints of twigs and branches.
      If you find sucking crawlers on your tree, I recommend the spray mix that I use for leaf miners. The mix is very powerful, topical and kills the bad guys and leaves the good guys alone.
      Check out my citrus Leaf miner article for more details.

      Potted challenges:
      Growing citrus in pots can be rather challenging.
      There is less room for error when fertilizing and watering a potted citrus.
      In addition a root bound plant will start to decline and may never fruit well regardless of how well you water or fertilize.
      If you are growing in pots, I would try to get dwarf varieties, grow in the biggest container possible, watch the soil closely, and apply frequent doses of dilute organic fertilizer. The above mentioned fertilizer recommendation has micronutrients mixed in.
      However, another great general organic fertilizer option is:
      Neptune’s Harvest Organic Hydrolized Fish & Seaweed Fertilizer 36 0z

      Not ripe yet:
      Another option is that the fruit may just not be ripe yet.
      Citrus actually take a long while to ripen… 9 months or so depending on the growing conditions and variety.
      They may just not be ready yet.
      Sometimes this can be hard to tell. However, unripe fruit will be hard and the skin will not be as shinny.

      Ripe but still a bit of green:
      This is actually pretty common.
      Citrus of all kinds may actually be ripe before they turn yellow (in the case of you Meyer lemon) or orange, etc.
      This is a bit unexpected because the ripe lemons at the stores are not green at all… well, sometimes, commercial growers often use artificial coloring to make the fruit more attractive (less green).

      Anyhow, lemons may still have some green on them when they are actually ripe.
      Look for that shine on the skin that may indicate that they are ready.
      The fruit should also not be rock hard and the fruit should give a bit when squeezed…
      But if they give too much when you squeeze them, you might have missed the window and they may be over ripe.
      This is a difficult thing to describe in written form and takes a bit of practice.
      If you are not sure, just test one out.

      Good luck!

      • Some citrus like oranges actually need a bit of cold that’s not frost to color up. They are the same as the green skinned orange fleshed oranges you can find in Thailand. Not related, but did you know that if you let a lime ripen further, then it will turn yellow like a lemon? Of course it’ll taste like a lime, so you could trick people.

        • Thomas Osborne, MD

          Thanks Nate

          This is interesting stuff.
          Yea, this is true for some but not all citrus. Cold can help both the skin and flesh color up depending on the variety. I believe I also talk about his a bit in the blood orange article.

          Yea, I am also very familiar with limes turning yellow. It can be a big surprise if you dont know about it.
          I talk about this a bit in my Bearss Lime article.
          On a very similar note, a reader was grateful after reading the Bearss Lime article because she discovered that she actually had a lime tree and not a lemon as she previously thought.

  2. My 2year old dragonfruit plants did flower this year with hopes of producing fruit. However, I noticed a brown 2-3 in.section on the branches that is soft and mushy. When I squeze it water runs out. I took a stic
    k and scraped off this brown slime to the spine of the branch. Any idea what this is? Did I over water?

    • Thomas Osborne, MD

      Hey Georgie
      Thanks for the great question.

      Well, you are not alone.
      This has happened to me… and many others too.
      My experience is that is happens randomly to the ends of branches.
      Usually one out of 50 branches or so.

      At first I felt this was a major danger because I have seen this type of thing move like cancer in other cacti.
      Therefore, I would quickly cut off the dead branch and make sure I had clean margins.
      However, One day I just decided to see what would happen on a branch if I didn’t do anything.. and well… it didn’t spread.

      That being said, its probably a good idea to cut these brown mushy branches off anyways.
      I would also clean/sterilize your cutting tools when your done so you dont spread any disease.

      So what causes this dragon fruit brown stem problem?
      My gut thought is that it is some kind of infection. Likely fungal, possibly bacterial.

      Unfortunately, bacteria and fungi are everywhere… so you cant avoid it.
      A healthy branch has a skin that will keep these bad guys out.
      However, if that skin is injured then there is an opening for problems.

      Therefore, infection usually penetrates weakened or injured branches.
      There are many potential causes of branch injury.
      Bugs may take a bite, resulting in a break in the skin where bacteria/fungi can get in.
      Too much fertilizer can cause rapid growth that will can make branches more susceptible to injury… and then infection.
      Sunburn can also cause injury that would allow bacteria/fungus to infect a branch.

      I dont think the cause is too much water, at least for what I am seeing.
      These cactus can handle a lot of watering as long as the soil has excellent drainage.
      Note, water/soil drainage problems usually cause the cactus to rot from the bottom up.
      What I am seeing happens at the ends of branches.

      Please let me know if you have any additional insight.


  3. One of the techniques we use in AZ is deep watering. By watering heavily and thoroughly, but less often, it improves drought tolerance as roots dig deeper for water. You can measure the amount you have watered by getting a metal rod or similar and pushing into the soil near, but not on the root ball. Soft soil is wet, and as you get deeper, the layer of hard soil is dry. It is best to repeat in multiple areas for results.

    • Thomas Osborne, MD

      Great. Deep infrequent watering is definitely the way to go for the reasons you mentioned.
      In addition, deep watering also helps to prevent salt buildup in the soil.
      Your metal rod idea is a great one. Thanks for the suggestion!

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