Originally and chiefly used in politics, the British-English phrase to kick something into the long grass means: to halt or stall a plan or project, so as to postpone having to make a decision, or take action, regarding it.
—American-English synonym: to kick the can down the road.

The phrase to kick something into the long grass occurs, for example, in the following from The Scotsman (Edinburgh, Midlothian, Scotland) of Friday 1^st January 1999:

How home rule plan was kicked into ministerial long grass

Matt Wells
Backroom lobbying by a fiercely anti-devolutionary Scottish secretary and a senior Whitehall civil servant scuppered early plans for home rule despite a sharp surge in support for nationalism in the 1960s.
Winnie Ewing’s sensational victory in the 1967 Hamilton by-election, when she became the first Scottish National Party MP to take up a seat at Westminster, shocked ministers into taking her party’s threat seriously.
But some judicious political manoeuvring by Willie Ross, who vehemently opposed any concessions to devolutionists, and Sir Burke Trend, then the cabinet secretary, ensured that the issue was kicked into the long grass of ministerial committees and constitutional commissions for a decade.

In to kick something into the long grass, the image is of sending a ball into the tall grass off the playing field during a sporting event, which interrupts this event—the use of the verb kick suggests that this phrase may refer specifically to football or rugby.

Such incidents did happen—as mentioned, for example, in the column Sports Shorts, published in the Orkney Herald (Kirkwall, Orkney, Scotland) of Tuesday 27^th July 1948:

MOWER NEEDED.
At a recent Parish Cup game in Bignold Park, a linesman lost the ball in the long grass (off the pitch), and the game was held up for some time till it was found.

The earliest occurrences of to kick something into the long grass that I have found are as follows, in chronological order—quotations 1 to 5 are from Hansard, the official report of all Parliamentary debates:

1, 2 & 3-: From debates that took place in the House of Commons:

1-: On Tuesday 29^th May 1962:

Mr Rippon *: The Motion of my hon. Friend the Member for Harwich (Mr. Ridsdale) called for a committee. The Motion at the Conservative Women’s Annual Conference simply called for the Government seriously to consider the present rating system. The difficulty about a committee is that it is apt to knock the ball into the long grass and produce some years later an unacceptable report.

* Geoffrey Rippon (1924-1997) was a Conservative politician.

2-: On Tuesday 24^th May 1966:

Mr Rippon: How long are the Royal Commissions expected to take to complete their work? In other words, how long is the ball to be kicked into the long grass?

3-: On Wednesday 23^rd November 1966:

Mr Rippon: The Government have passed the buck to Sir John Maud and his fellow Royal Commissioners. No doubt the Government will try to bury the report when they get it.
When the Prime Minister announced the names, I commented that it was an exercise—and it is an exercise, in kicking the ball into the long grass.
[…]
Mr Murton: The Royal Commission has much work to do and its terms of reference are extremely wide. I doubt very much whether it can achieve its object in two years. I deprecate the fact that many local authorities which have done much work should have their work discontinued and should be frustrated. Do the Government want radical reconstruction? If they receive radical proposals will they have the courage to put them into effect? Will they bring them before the House as a basis for legislation and not as my right hon. and learned Friend the Member for Hexham (Mr. Rippon) said, “Kick the ball once more into the long grass”? That is a good expression because when a ball is kicked into the long grass it is lost. If this “ball” is lost it will mean that more time and money will be wasted and there will be more frustration. Then we shall be back where we started.

4-: From a debate that took place in the House of Lords on Wednesday 20^th December 1967:

Lord Hill of Luton: Please spare this body from having to go periodically to the Ministry, and through the Ministry to the Treasury, for instalments of money. […]
[…] I warmly wish the noble Baroness, Lady Serota, a happy and successful tenure of what is bound to be a most challenging but important office, and if she were in her place [sic] I would urge her to get the cash settled in advance to avoid the risk of the ball being perpetually kicked into the long grass of Treasury discussion.

5-: From a debate that took place in the House of Commons on Tuesday 12^th November 1968:

Mr Rippon: What is the use of having these Constitutional Commissions or Committees on Public Participation in Planning and then introducing an Order of this kind which deliberately cuts down public participation? While all these stage armies of paper tigers who serve on these multifarious advisory bodies are leisurely employed in hitting all these balls into the long grass, the Government continue the steady progress, which they have made ever since they took office, of widening the gap between themselves and the people they seek to govern.

6-: From Rippon team to bring planning laws up to date, by The Daily Telegraph’s local government correspondent, published in The Daily Telegraph (London, England) of Thursday 4^th October 1973:

A sweeping review of “outdated” town and country planning laws was announced yesterday by Mr Geoffrey Rippon, Secretary for the Environment.
The review will be carried out under the chairmanship of Mr George Dobry, Q C, who was a founder member of Justice, the organisation which protects individual rights.
[…]
Although there are now over 250 inspectors to hold public inquiries the problem is still to find people of the right calibre. The committee is being set up because Mr Rippon did not want to kick the ball into the long grass and await a Royal Commission.