Problematic over-potting

[Darold Petty]

Recently I had the good fortune to acquire a well-grown Laccospadix, suckering form.  I needed one more to complete my landscape design for a corner of my garden.  The plant came to me in a "15 gallon" pot.  Although full and well grown, it seemed to be in too large a pot.  Palms from Southern California growers are often sold this way,  leading to the joke that one is "purchasing a small plant, with a lot of very expensive potting soil!"

  let's compare pot sizes.  The 15-gallon is not truly a  15 gallon by liquid volume, and measures 14 inches diameter by 17 inches tall.  (36cmx43cm).

The pot I prefer is a Pro-Cal #7 Tall, measuring 11.5 inches diameter by 14 inches tall. (29cmx36cm)  So, the smaller pot has 80% of the height but only 56% of the volume. 

This is important because a small root system in a large pot volume will have difficulty utilizing all the retained moisture, and even worse, if the medium does get really dry then some areas will remain completely dry and become truly hydrophobic,  causing future irrigation to run through only the moist areas.

When I tipped the palm out of the 15 gallon pot this was the case, and the worst example I have encountered.  Some of the medium was saturated, and a large volume within the rootball was hydrophobic. It was so dry, that it just drained away from the roots like pouring dry sand out of a container.  I re-potted the palm into the smaller pot, using mostly the dry medium, as it was easier to pack around the roots and more certain to fill completely without voids.  Then, I had the problem of effective wetting, for this I like to soak the entire pot in a much larger container so that the water level is the full height of the smaller pot.  I leave it to soak for 24 hours.

  Here are some images, the saturated medium was mostly along one side of  the 15 gallon pot  and the bottom several inches. The hydrophobic medium was much lighter in color.

  Many growers feel that a larger pot volume with more room for root extension will produce faster growth, I don't agree.  The larger volume does reduce the frequency of irrigation labor.  I like the smaller volume, and more incremental increases in pot volume.  This will also allow addition of fresh medium more frequently, counteracting the leaching of nutrients by the irrigation.

  This has worked really well for me.  I have purchased palms so oversized that the pots had to be cut off.  This is not an issue, as the subsequent roots erupt higher above the older ones, so a solid mass of roots doesn't negatively effect future root growth.   I have 'down-sized' plants of Chamaedorea, Howea, Chamaerops, and now Laccospadix with no losses.   However, I would not attempt this with genera known to have more sensitive roots, such as Brahea or Bismarkia.   This can also be a helpful technique if one cannot dig such a large hole as the palm was potted upon acquisition.

Just to be compulsive, I will leave this palm in my greenhouse for a few months before ground planting  I did this downsize three days ago, and the spear on the main stem has already increased an inch (2.54cm).  

 

[Las Palmas Norte]

Nice rescue. This topic rarely is discussed and is every bit as important as the top growth. It can also be the problem when diagnosing plant issues. Palm health requires an understanding below the soil level as well as above. Conversely, I've purchased palms that were so crowed in undersized pots that there was very little soil remaining in the pot.

[happypalms]

The correct pot size with palms is critical to good health. I have observed with 70mm round tubes are better for seedlings than 70mm square tubes. Long deep tubes for certain remote germinating palms or the tiny 50mm square or round tubes all make a difference for tiny seedlings to large ones. Knowing your seedlings is the key. A overgrown root bound palm performs better than a loose fitting roots when potted up correctly. 70mm tubes won’t grow in a 200mm container. I pot a lot of palms up basically into the next size up. 140mm into 200mm provided there is a root ball. All too often I see overpotted palms suffer basically from lack of oxygen being to wet the roots sour and it’s game over for the palm.