Green Roof Plants, Rain-Root Zone and Root Architecture

One of our favorite Florida #Greenroof plant Genus is the Allium genus.  We've also been working with Resurrection fern also - and I love this plant.  Resurrection fern,  Polypodium polypodioides, was the first fern in space - going up on a 1997 Space Shuttle Mission to see if the roots would absorb water in a space capsule.

Green Roof Plant Root Architecture - Florida Extensive Green Roofs - MetroVerde

Both of these plants, the Allium and R. fern can have unique root characteristics, depending on how they are raised by the grower.

We call plant root structure by the name - 'Root Architecture'.

Green roof design has unique root structure and root architecture requirements.

Unless you have an unlimited potable water or well water source and are going to pump all that water up on a roof to keep plants up there watered, then your green roof plants need to be somewhat drought tolerant.

Certain root architecture patterns support plant acclimation to drought conditions better than others.

Remember, Florida's rainfalls usually are short, afternoon events of 1/2" or less and because rain generally occurs between the hotter months of the year - June - September, there is a tendency for it to evaporate quickly.

Except for hurricanes and tropical storms, rain events in Florida are usually over relatively quickly.

Meaning green roof plants have to scramble to grab the rain water.

Also recall, most green roof plants do not like wet roots (wet feet) so the soil must be well drained.

Proper green roof plant root architecture is crucial for providing a Florida extensive green roof plant with the advantages needed to survive a Florida vegetated roof.

Examine the diagram below showing the root architecture of a green roof plant raised in a one gallon standard nursery container and then a green roof plant raised in a built-in-place green root extensive planting bed.

The plant raised on the built-in-place green root extensive planting bed possesses 8 times the amount of Root-Rain surface contact area as the same size plant grown in a nursery container.

So when the afternoon 1/2" rainfall (13mm) event occurs and every drop is important - the green roof plant with the appropriate root architecture will sequester the most water.

More stormwater is captured, runoff is reduced, plants acquire necessary water volumes, plants have less of a tendency to uproot in high winds, and more.

Green Roof Plant Root Architecture is important to the success of a green roof.

Florida Green Roof Plant Root Architecture - Think Lateral!

Florida Green Roof plant root architecture and the converse relationship to irrigation is an important design function for the Green Roof professional to understand.

We've been working with Resurrection fern as a Green Roof plant for Florida and the tropics - and I love this plant.  Resurrection fern,  Polypodium polypodioides, was the first fern we know of in space - going up on a 1997 Space Shuttle Mission to see if the roots would absorb water in a space capsule.

Both of these plants, the Allium and Resurrection fern have unique root characteristics.

We call plant root structure by the name - 'Root Architecture'.

Green roof design has unique root structure and root architecture requirements.

Unless you have a huge potable water or well water source and are going to pump all that water up on a roof to keep plants up there watered, then your green roof plants need to be somewhat drought tolerant.

Certain root architecture patterns support plant acclimation to drought conditions better than others.

Remember, Florida's rainfalls usually are short, afternoon events of 1/2" or less and because rain generally occurs between the hotter months of the year - June - September, there is a tendency for it to evaporate quickly.

Except for hurricanes and tropical storms, rain events in Florida are usually over relatively quickly.

Meaning green roof plants have to scramble to grab the rain water.

Also recall, most green roof plants do not like wet roots (wet feet) so the soil must be well drained.

Proper green roof plant root architecture is crucial for providing a Florida extensive green roof plant with the advantages needed to survive a Florida vegetated roof.

Examine the diagram below showing the root architecture of a green roof plant raised in a one gallon standard nursery container and then a green roof plant raised on a green root mat.

The plant raised on the mat possesses 8 times the amount of Root-Rain surface contact area as the same size plant grown in a nursery container.

Green Roof Plant Root Architecture - Florida Extensive Green Roofs - MetroVerde

So when the afternoon 1/2" rainfall (13mm) event occurs and every drop is important - the green roof plant with the appropriate root architecture will sequester the most water.

More stormwater is captured, runoff is reduced, plants acquire necessary water volumes, plants have less of a tendency to uproot in high winds, and more.

So think lateral.  Think horizontal.  Experiment with green roof planting designs that encourage outwards rather than downward root growth.

Green Roof Plant Root Architecture is important to the success of a green roof.

Green Roof Root Architecture, Understanding Water Adsorption

Today brought the monthly watering of a 1/4" H2O for the Alliums.  Within a matter of hours they were bright green.

We've been working with Resurrection fern also - and I love this plant.  Resurrection fern,  Polypodium polypodioides, was the first fern in space - going up on a 1997 Space Shuttle Mission to see if the roots would absorb water in a space capsule.

Both of these plants, the Allium and Resurrection fern have unique root characteristics.

We call plant root structure by the name - 'Root Architecture'.

Green roof design has unique root structure and root architecture requirements.

Unless you have a huge potable water or well water source and are going to pump all that water up on a roof to keep plants up there watered, then your green roof plants need to be somewhat drought tolerant.

Certain root architecture patterns support plant acclimation to drought conditions better than others.

Remember, Florida's rainfalls usually are short, afternoon events of 1/2" or less and because rain generally occurs between the hotter months of the year - June - September, there is a tendency for it to evaporate quickly.

Except for hurricanes and tropical storms, rain events in Florida are usually over relatively quickly.

Meaning green roof plants have to scramble to grab the rain water.

Also recall, most green roof plants do not like wet roots (wet feet) so the soil must be well drained.

Proper green roof plant root architecture is crucial for providing a Florida extensive green roof plant with the advantages needed to survive a Florida vegetated roof.

Examine the diagram below showing the root architecture of a green roof plant raised in a one gallon standard nursery container and then a green roof plant raised on a green root mat.

The plant raised on the mat possesses 8 times the amount of Root-Rain surface contact area as the same size plant grown in a nursery container.

Green Roof Plant Root Architecture - Florida Extensive Green Roofs - MetroVerde

So when the afternoon 1/2" rainfall (13mm) event occurs and every drop is important - the green roof plant with the appropriate root architecture will sequester the most water.

More stormwater is captured, runoff is reduced, plants acquire necessary water volumes, plants have less of a tendency to uproot in high winds, and more.

Green Roof Plant Root Architecture is important to the success of a green roof.

Green Roof Plant Root Architecture

A while back we looked at green roof plant root architecture and the benefits of green roof plants possessing a broad, shallow root structure rather than a narrow, deep root structure.  Click here to review the blog post information.

The diagram is posted for review here.

Green Roof Plant Root Architecture Comparison - MetroVerde

Real life Green Roof Plant photos of the two types of root architecture are posted below:

Root Architecture - Poor Green Roof Formation 

The photo above typifies the normal nursery container plant root structure - narrow and deep.  This is not a good root formation or architecture to begin a green roof with.  Note the following photos of a plant grown on a mat.  I've cut the mat out of a green roof that had a 2" engineered soil layer.  The plant had grown on the roof for approximately 3 years or longer.  The green roof system was non-irrigated.

Green Roof Plant - Root Architecture 1 - MetroVerde

Green Roof Plant - Root Architecture 2 - MetroVerde

Green Roof Plant - Root Architecture 3 - MetroVerde

Green Roof Plant - Root Architecture 4 - MetroVerde

When I removed the mat section I cut out about twice the diameter of the plant crown or habit (form diameter) thinking I'd capture all the root mass.  Upon further examination the plant had extended its roots over triple the area I'd cut.

Note how the roots have grown and woven themselves into the mat - providing an anchor against high winds and allowing for use vertically.

The root architecture of plants grown in mats exemplifies the benefits of growing green roof plants in mats.  Roots do not like to be bound up with limiting walls.  It you do not use mats, then use large tray systems.

With time, green roof plants with access to a large, monolithic and non-sectioned growing space will eventually 'move' to the best spot for their particular needs - on the roof.

The same basic principle applies to living walls.  A monolithic fabric with no limiting sectional structure will allow the plant to choose the best spot for successful, long tern growth.

Green Roof Plants - What Makes Roots Happy?

Removing older green roofs to allow for a new project has opened my eyes to the way green roof plant roots grow.  Root growth science is also know as 'root architecture'.  

As you can see, roots do not like to be constrained.  Though all roofs have a perimeter and roots must eventually reach a boundary, allowing the plants to reach out for  nutrients and water offers many benefits!

Tomato plant roots reaching out horizontally in the Green Roof hurricane weave

Having grown plants in pots for decades I can say with no uncertainty root bound plants are prone to disease and do not preform well in the long term.

Pot bound roots spiral around and around looking for room to grow

Green Roof trays must be large to prevent root binding patterns

Normal root architecture is best achieved by open growing systems on Green Roofs

To me, a photo is worth a thousand words and it is easy for me to see how roots want to stretch out.  Of course we've discussed the many benefits of horizontal root architecture in previous posts.  An example  of a shallow green roof application can be found here.

Let your green roof roots grow.  If you use a tray system make sure the trays allow for root crossover through adequate openings.

Roots need oxygen too.  When roots grow too deep or are strangled by other roots due to a lack of horizontal growing room the plants can suffer.  Providing adequate horizontal growing room ensures good plant development, unless you are using tap root plants (not too many of these are appropriate for green roofs).

Plants for Florida Green Roofs - Root Architecture - Rain-Root Zone

Today brought the monthly watering of a 1/4" H2O for the Alliums.  Within a matter of hours they were bright green.

We've been working with Resurrection fern also - and I love this plant.  Resurrection fern,  Polypodium polypodioides, was the first fern in space - going up on a 1997 Space Shuttle Mission to see if the roots would absorb water in a space capsule.

Both of these plants, the Allium and R. fern have unique root characteristics.

We call plant root structure by the name - 'Root Architecture'.

Green roof design has unique root structure and root architecture requirements.

Unless you have a huge potable water or well water source and are going to pump all that water up on a roof to keep plants up there watered, then your green roof plants need to be somewhat drought tolerant.

Certain root architecture patterns support plant acclimation to drought conditions better than others.

Remember, Florida's rainfalls usually are short, afternoon events of 1/2" or less and because rain generally occurs between the hotter months of the year - June - September, there is a tendency for it to evaporate quickly.

Except for hurricanes and tropical storms, rain events in Florida are usually over relatively quickly.

Meaning green roof plants have to scramble to grab the rain water.

Also recall, most green roof plants do not like wet roots (wet feet) so the soil must be well drained.

Proper green roof plant root architecture is crucial for providing a Florida extensive green roof plant with the advantages needed to survive a Florida vegetated roof.

Examine the diagram below showing the root architecture of a green roof plant raised in a one gallon standard nursery container and then a green roof plant raised on a green root mat.

The plant raised on the mat possesses 8 times the amount of Root-Rain surface contact area as the same size plant grown in a nursery container.

Green Roof Plant Root Architecture - Florida Extensive Green Roofs - MetroVerde

So when the afternoon 1/2" rainfall (13mm) event occurs and every drop is important - the green roof plant with the appropriate root architecture will sequester the most water.

More stormwater is captured, runoff is reduced, plants acquire necessary water volumes, plants have less of a tendency to uproot in high winds, and more.

Green Roof Plant Root Architecture is important to the success of a green roof.

Tomorrow - Actual photos of green roof plant root architecture styles.

Email me with questions by clicking here.

Happy Green Roofing!  Kevin