• Above is a true picture of a tree's root system & how it extends out.
• Up to 40% of a tree's biomass is underground.
• Most roots grow closer to the soil surface than you think. Sometimes within the top 6 inches.
• When space is available, roots will extend out 2 to 3 times the reach of the branches.
• Roots absorb nutrients & water, store carbohydrates, & stabilize a tree's trunk & canopy.
• Growth regulators, produced in the roots, affect growth in the upper part of a tree.
• Studies show that 75% of a plant's potential for survival depends upon the root system.

The roots of the above eucalyptus start to grow up the bank, then grow out & down the slope.
This is the way roots grow on steep slopes. This is why large trees on steep slopes fail.

Roots grow sideways and then down banks. They do not grow straight into the bank because of nutrional requirements (oxygen, water, etc.). They also do not grow very far up a bank. This is due to geotropism, which is the gravitional effect on growth regulators within the roots.That is why roots grow down.
The roots that "hold" a tree up grow in the opposite direction. Therefore, they actually "pull" a tree up. With no roots going into the bank, but rather down, you see most tree failures, on steep banks, fall in the lower 180 degrees of the slope. So do not allow trees on slopes to get too big or better yet, plant trees that don't grow as large. Check it out next storm!

GRASS & TREES

This live oak had been here for over 150 years until a lawn was put around it. The increased irrigation necessary for the grass was not compatible with this species. It led to the spread of Armallaria mellea, oak root fungus, which decayed the roots and led to complete tree failure. The decayed root stubs can be seen
on the stump. Fortunately, no one was injured.

MULCH

Organic mulch is possibly the best and least
expensive soil enhancer around. This is the way
nature does it, as a tree mulches its own root
system, returning nutrients to the soil.

A mulch covering should be 2 to 4 inches deep
and extend outside the dripline.

Decomposing mulch may be all the
nutrients your tree will ever need.

Mycorrhizae

Mycorrhizae are fungi that form a symbiotic relationship with the root system of a plant. Mycorrhizae:

• increase the absorbing capacity of roots up to 700%,
• mycorrhizae are also able to access water in micropores in soil that are too small for roots. This is a survival strategy for many native oaks growing on decomposed granite slopes.
• increase a roots tolerance to drought, high soil temperatures, and a variety of soil toxins, high salinity, & heavy metals
• It is more efficient for a tree to support mycorrihzae than to produce the equivalent amount of roots.

Above, the hyphae or fungal strands
of the mycorrihzae are growing out of the root. These
strands absorb nutrients & water from the soil for the
roots in exchange for carbohydrates from the roots.

1. The top 8-12 inches of soil should be kept evenly moist within and just outside the dripline.
2. Water should be applied slowly (without run-off) within and just outside the dripline.
3. Established trees only need to be watered every two to four weeks depending on the species and assuming watering was done as noted above.