Short answer. You must expressly reserve the right to repurchase in the contract of sale itself. Article 1601 of the Civil Code defines conventional redemption as the situation where the vendor reserves the right to repurchase — it does not arise automatically and cannot be created after the sale is already complete.
What the law says
Conventional redemption shall take place when the vendor reserves the right to repurchase the thing sold, with the obligation to comply with the provisions of article 1616 and other stipulations which may have been agreed upon.
Civil Code, Article 1601 — What Conventional Redemption Is. Read the full provision →
What conventional redemption is
Article 1601 defines conventional redemption as a right that arises when the vendor — the seller — expressly reserves the right to repurchase the thing sold in the contract. This is also called a pacto de retro. It transforms what looks like an outright sale into a conditional transfer: the buyer gets the property, but the seller retains the option to reclaim it by paying back the price and certain other amounts within the agreed period. The reservation must be part of the sale itself — it cannot be added later as a separate arrangement.
What you must pay to exercise the right
Reserving the right is only the first step. To actually exercise it — to buy the land back — the vendor must return to the buyer the price of the sale, plus the expenses of the contract and any other legitimate payments the buyer made by reason of the sale, plus the necessary and useful expenses the buyer made on the property itself. Article 1616 lists these obligations. If you reserved the right but cannot meet these payment requirements when you try to exercise it, the redemption fails and the buyer's title becomes absolute.
The time limit on the right
Conventional redemption must be exercised within the period agreed upon in the contract. The parties are free to set this period, but the Civil Code caps it: the right of repurchase cannot be exercised beyond ten years from the date of the contract. If no period is stated in the contract, the right expires four years from the date of the sale. Once the period lapses without the seller exercising the right, the buyer's title becomes unconditional and the right is permanently lost. The deadline is strict — there is generally no extension.
Practical steps before you sign
If you want a right to buy your land back, the time to secure it is before the sale is signed — not after. Have your lawyer draft a clause in the deed of sale that expressly reserves your right to repurchase, states the period within which you may exercise it, and identifies any conditions. The clause should be clear and specific; an ambiguous redemption clause can lead to disputes about whether it was validly reserved and what its terms were. Once the deed is signed without a reservation clause, the right of conventional redemption is gone.