How deep do palm roots go?

[WisTex]

How deep do palm roots, specifically Washingtonia and Sylvestris, go down, not how wide?   North Padre Island has a fresh water layer under it, 5 to 9 feet down.  Mature Washingtonia and Sylvestris do very well here.  wondering if that could be part of the reason.

Edited October 29, 2023 by WisTex

[Dwarf Fan]

  On 10/29/2023 at 4:34 PM, WisTex said:

How deep do palm roots, specifically Washingtonia and Sylvestris, go down, not how wide?   North Padre Island has a fresh water layer under it, 5 to 9 feet down.  Mature Washingtonia and Sylvestris do very well here.  wondering if that could be part of the reason.

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Hello neighbor, that is a question I have often wondered about myself, a Google search brings up a depth of about 3 to 6 feet long for most Palm species. However, I have read Bismarckia & CIDP can have an even larger root system when mature.

Palmco website says: 

Palm Tree Root Systems

Palm trees are unique in that their roots generally do not continue to spread out as the tree grows taller. Even the tallest of palm trees (including the Washingtonia Robusta, or Mexican Fan Palm, which can grow up to 100 feet), will have the same width of root system as a much smaller palm tree.

There is a specialized area around the base of the tree where the roots continue to grow and die off. 

This is known as the “root initiation zone.” 

This zone is generally about 40 inches around the base of the tree, and the roots are not far below the soil. Ideally, the soil will have lots of air pockets and moisture to encourage growth.

On palmvrienden website it says that generally the longest roots are about 6’ especially if there is ground water present.

The root system

Palms are monocots and therefore have a different root system than a typical deciduous tree. This is reflected not only in the different approach to the planting itself, but also in the further development of the root system.

The seedling develops differently as early as germination. From the seed emerges a hyperphyll which will divide in a coleoptil (ligule) from where the first leaf emerges and a radicle which is the first real root. Afterwards, the roots develop further with special functions depending on their position and depth in the soil. We divide the root system, the rhizosphere, into 4 zones.

Zone I

http://palmvrienden.net/lapalmeraie/files/2016/04/roots-230x300.jpg

The respiratory zone. This zone is no more than about 25 cm (1 ft) deep and reaches a maximum of 50 cm (1,8 ft) from the trunk. We find here both primary and secondary geotropic roots. In other words, they are led downwards by gravity. In this zone we also the transition from stem to roots and the root tuber.

Zone II

The nutritional zone. The largest area of the rhizosphere and also containing the highest proportion of primary and secondary roots. The zone stretches between 90 and 150 cm (2 ft 11 in – 4 ft 11 in) in depth and width and reaches just a bit further in width than the palm leaves.

Zone III

The absorbing zone. The exact development of this root zone is highly dependent on the species and depth of groundwater. Normally this zone is about 150 to 180 cm (4 ft 11 in – 5 ft 11 in) deep. This zone contains mainly primary roots and the root density is significantly lower than in zone 2. Just like in zone 2, the actual absorption is also done here by the very fine root hairs.

Zone IV

The development of the last zone depends entirely on the groundwater level. In areas where the groundwater is high, there is hardly any distinction between zone 3 & 4.

[mnorell]

The idea that huge palm like Washingtonia robusta would have a narrow-diameter root-system similar to much smaller palms truly strains credulity. Basic logic (and physics) informs us that a palm such as Washingtonia robusta or a tall Cocos will require a very broad field of roots just for their physical stability. Per Broschat and Melrow, "Palm roots are capable of significant lateral growth; roots of some palms have been measured well over a hundred feet from the parent trunk." A friend of mine on the Long Beach strand on Big Pine Key (in the Florida Keys) discovered to his chagrin that his beachfront house had lost all of its sandy beach after a major hurricane (either Georges or Wilma), but he marveled at the suddenly revealed, huge net of roots spreading out from his coconut trees. He said the fibrous root system extended at least 100', well beyond his property boundaries. This is certainly a factor in the ability of these trees to withstand almost unbelievable wind-forces and remain firmly in the ground and upright.

Also, the "root initiation zone" does not refer to the width of the root-system, but rather to the zone at the physical base of the stem/trunk in which roots are initiated (and this can be a constantly regenerating area of new roots to replace those older roots that die off or are physically damaged). This zone can extend upward along the trunk for some distance in cases of stilt-root palms, or along the ground-facing stems of "crawling" palms such as Serenoa. 

Clustering, small palms will of course have a very different root-zone from tall/massive solitary palms...and details will depend on whether they are growing in desert, mesic, seasonally flooded, rainforest, etc. environments. And so it follows that palms from very dry areas (or seasonally wet/dry areas with extended droughts) will need to have roots that can tap into groundwater supplies, as WesTex suggests. A palm like Washingtonia robusta, which pops up in the cracks in bone-dry, almost completely impermeably paved parking lots across Southern California, or in the searingly hot, dry desert of Palm Springs, must additionally have the ability to send down very deep roots to locate groundwater. Some of these groundwater resources will be quite deep.

So, in short, every palm will likely be different in the details and scope of its root-system, and it is best to consider each species--indeed, each specimen--on its own, and within its individual circumstances, rather than rely on generalizations of dubious origin. Plants will do what they need, within their own physical limits, so I think the answer for any palm is just "follow the water, stand up to the wind." Whatever it takes to survive.

[WisTex]

  On 10/30/2023 at 6:27 AM, mnorell said:

A palm like Washingtonia robusta, which pops up in the cracks in bone-dry, almost completely impermeably paved parking lots across Southern California, or in the searingly hot, dry desert of Palm Springs, must additionally have the ability to send down very deep roots to locate groundwater.

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A large percentage of homes on North Padre have palms completely surrounded by concrete or other hard surface.  If not hard surfaced, then rocks over impermeable plastic.  That's why I am wondering how palms obtain moisture, and if there is a difference in palm species.  North Padre's climate is hot, high humidity, windy, semi-arid with occasional rain deluges, hurricanes, arctic outbreaks....and rarely, but it happens, snow.  

[flplantguy]

I'm hoping they root down to water as my sand is dry but only at 20 feet elevation or so, and at 13 feet is wetlands and a spring within walking distance, so they can be dry above with moisture below if they root to it.  no idea if that will happen or not but there are plants in the ground to find out.

[Merlyn]

  On 10/30/2023 at 12:47 PM, WisTex said:

A large percentage of homes on North Padre have palms completely surrounded by concrete or other hard surface.  If not hard surfaced, then rocks over impermeable plastic.  That's why I am wondering how palms obtain moisture, and if there is a difference in palm species.  North Padre's climate is hot, high humidity, windy, semi-arid with occasional rain deluges, hurricanes, arctic outbreaks....and rarely, but it happens, snow.  

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If the fresh groundwater is only 5-9 feet below the surface, I'd expect every large palm has tapped into it.  When I transplanted a couple of barely-trunking Sylvestris they had HUGE root masses at 3 feet deep.  The groundwater at my property is also around 6 feet down, so even a relatively young Sylvestris was definitely hitting the water table.