Hi slider,
This is quite a complicated answer, and once you have read it you may prefer to go down the path of trying to obtain permission anyway.
The actual copyright status of this poem today will depend on when it was written. Put simply, the copyright status of a work is determined by where it was written, as well as by whom it was written. Juan Ramón Jiménez Mantecón was born in Spain, but in 1916 at the age of 35 or thereabouts, he moved to Portugal. Then in 1946 he moved to Puerto Rico and lived there for the remainder of his life. Thus his poems could have been been originated under Spanish, Portuguese or American copyright law, depending on the date they were written. American law because Puerto Rico has, since 1901, been an
American territory and US Federal law prevails there.
Each of these nations has or had a different length of copyright term. At the relevant times, Spain's copyright term was the lifetime of the author plus 80 years, Portugal's was the lifetime plus 50 years and the USA operated a system which relied on registration; if registration was carried out correctly, copyright could last for up to 56 years from the date the poem was written, but if the work was not correctly registered, it would get no copyright, and if the registration was not correctly renewed, it would only have lasted for 26 years from the date of creation. With some patience, you can check online to see if a work was registered and renewed, via the
US Copyright Office website.
So, really messy. For example if this particular poem was written while Jiménez was in Portugal, the poem would now be out of copyright, since he died in 1958, but for the change in EU law which occurred in 1995. If it was written while he was living in Spain, copyright will continue to exist until 2029 (there were some special transitional arrangements when Spain had to fall in line with other EU countries and set their term at the current EU length of lifetime plus 70 years). And the US situation is too difficult to guess, not knowing when or if the work was registered.
The complications don't end there. You have quoted an English language version. If this is the language that Jiménez wrote it in, or he made this translation, then all of the above holds true. However, if someone else translated the work into English, then they are the owner of the copyright in the translation, and thus the term of the copyright for the English version has to be based on their lifetime and the country where they were when they made the translation, and it will be from the translator, or his/her heirs, that you need to get permission.
However help is at hand. The new
section 30 (1ZA) of the UK Copyright Designs and Patents Act allows for the quotation of copyright works as long as the author is credited, and the amount quoted is fair. Given that this is a short poem, it is possible that quoting it in its entirety would be fair, and if so, then you would not need permission, assuming that the poem is still in copyright. The quotation exception applies equally to the English or Spanish versions.
Amended on 24 January to clarify the current law in Portugal