COLUMBIA ACORN TRUST

Supplement dated March 1, 2013 to

the Statement of Additional Information dated May 1, 2012, as supplemented

Effective immediately the following is added to Appendix S of the Statement of Additional Information:

Additional Information about Systematic Withdrawal Plans

A Systematic Withdrawal Plan allows you to schedule regular redemptions from your account any day of the month on a monthly, quarterly or semi-annual basis. Currently, Systematic Withdrawal Plans are generally available for Class A, B, C, R4, R5, Y and Z share accounts. Contact the Transfer Agent or your financial advisor to set up the plan.

To set up the plan, your account balance must meet the class minimum initial investment amount. All dividend and capital gain distributions must be reinvested to set up the plan. A Systematic Withdrawal Plan cannot be set up on an account that already has a Systematic Investment Plan established. If you set up the plan after you’ve opened your account, we may require your signature to be Medallion Signature Guaranteed.

You can choose to receive your withdrawals via check or direct deposit into your bank account. The Fund will deduct any applicable CDSC from the withdrawals before sending the balance to you. You can cancel the plan by giving the Fund 30 days’ notice in writing or by calling the Transfer Agent at 800.422.3737. It’s important to remember that if you withdraw more than your investment in the Fund is earning, you’ll eventually withdraw your entire investment.

Shareholders should retain this Supplement for future reference.