“We are still in the position of those who cut the forest and planted some seedlings, and now are surprised that there is no shade. Do I worry that there is no shade? I do. Am I working on making the trees grow? I am, but it cannot grow in one year.”

Edward Everett Hale in a statement published in A Year of Beautiful Thoughts‎ (1902) by Jeanie Ashley Bates Greenough, p. 172; <!-- and perhaps as early as an edition of Ten Times One is Ten (1870) by Hale--> This has been misattributed to Keller in published works since at least 1980. Keller and Hale were good friends, and letters to Hale can be found in her youthful autobiography The Story of My Life (1902). In 1910 Keller dedicated her poem "The Song of the Stone Wall" to Hale who had died in 1909.
Misattributed
Variant: I am only one, but I am one. I can not do everything, but I can do something. I must not fail to do the something that I can do.

Statement published in A Year of Beautiful Thoughts‎ (1902) by Jeanie Ashley Bates Greenough, p. 172, Third statement for June 11. This has often been misattributed to Helen Keller in some published works since at least 1980, perhaps because she somewhere quoted it.
Variant:
I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything,
I will not refuse to do the something that I can do.
The Book of Good Cheer : A Little Bundle of Cheery Thoughts‎ (1909) by Edwin Osgood Grover, p. 28; also in Masterpieces of Religious Verse (1948) by James Dalton Morrison, p. 416, where it is titled "Lend a Hand"
Variant: I am only one, but still I am one. I cannot do everything, but still I can do something; and because I cannot do everything, I will not refuse to do something that I can do.

Source: The Poisonwood Bible

Source: Morals and Dogma of the Ancient and Accepted Scottish Rite of Freemasonry (1871), Ch. XIX : Grand Pontiff, p. 312
Context: The true Mason labors for the benefit of those that are to come after him, and for the advancement and improvement of his race. That is a poor ambition which contents itself within the limits of a single life. All men who deserve to live, desire to survive their funerals, and to live afterward in the good that they have done mankind, rather than in the fading characters written in men's memories. Most men desire to leave some work behind them that may outlast their own day and brief generation. That is an instinctive impulse, given by God, and often found in the rudest human heart; the surest proof of the soul's immortality, and of the fundamental difference between man and the wisest brutes. To plant the trees that, after we are dead, shall shelter our children, is as natural as to love the shade of those our fathers planted.

"Address in Berkeley at the University of California (109)" (23 March 1962) http://www.jfklibrary.org/Research/Research-Aids/Ready-Reference/JFK-Quotations.aspx
1963

Human Knowledge: Its Scope and Limits (1948), p. 172
1940s

Malgudi Days(1943)

Source: No Longer at Ease (1960), Chapter 5 (p. 57)

What do we plant when we plant a tree?