Exhibit 99.1

FOR IMMEDIATE RELEASE

Rentech Announces Results for First Quarter 2015

Canadian Plants Begin Producing Pellets

LOS ANGELES, CA (May 11, 2015) – Rentech, Inc. (NASDAQ: RTK) today announced financial and operating results for the three months ended March 31, 2015.

Keith Forman, President and CEO of Rentech, stated, “Results for the first quarter were generally in line with our expectations for improved profits. At Rentech Nitrogen, margins improved in the first quarter from last year, due to robust demand for ammonia and ammonium sulfate, higher ammonium sulfate prices and lower natural gas prices.”

“At Fulghum, our cost controls are working and EBITDA margins have improved. We are also seeing strong demand for NEWP’s pellet products in the U.S. Northeast,” Mr. Forman continued.

“Our two Canadian wood pellet facilities are in commissioning. The Atikokan facility is supplying all of the required volume to OPG from its own production, and the pellets we are producing exceed the contract’s requirements for quality and energy content. Commissioning of the Wawa facility is going better than forecasted. We have completed integrated production runs, and we have run all 12 pellet mills at the plant. We loaded our first rail cars with pellets at Wawa, and they are ready to be transported to the port,” Mr. Forman added.

Summary of Results

The consolidated results of Rentech, Inc. include its wood fibre processing business and Rentech Nitrogen Partners, L.P. (NYSE: RNF) (Rentech Nitrogen). The wood fibre processing business consists of Fulghum Fibres (Fulghum); New England Wood Pellet (NEWP), which includes the recently purchased mill from Allegheny Pellet Corporation (Allegheny); and Industrial Wood Pellets, which includes our Canadian pellet plants, business development for industrial pellets, and senior management of the fibre business and corporate allocations. Rentech owns the general partner and approximately 60% of the limited partner interests of Rentech Nitrogen. Rentech Nitrogen’s operating segments are the East Dubuque, Illinois facility and the Pasadena, Texas facility.

Rentech Nitrogen’s results for the first quarter of 2015 benefitted from improved prices for ammonium sulfate and lower natural gas prices. Sales volumes for ammonia were significantly higher than in the first quarter last year. At Fulghum, lower South American product sales and reduced volumes at our U.S. and South American chipping facilities negatively affected results in the first quarter compared to the same quarter last year. Our two Canadian wood pellet facilities are in commissioning. Since the beginning of February, we have been satisfying all of our required deliveries to Ontario Power Generation (OPG) with pellets produced by our Atikokan facility. NEWP had a seasonally strong quarter due to good demand for wood pellets in the U.S. Northeast. During the first quarter, we paid $5 million in earn-out consideration to the previous owners of NEWP based on NEWP’s 2014 performance. We acquired the assets of Allegheny in January. In April, we borrowed an additional $7.5 million under the Tranche B term loan from GSO Capital to fund the Canadian operations.

NEWP’s and Allegheny’s operations are included in our operating results from May 1, 2014 and January 23, 2015, respectively, the closing dates of the acquisitions. Prior period revenues and cost of sales for Fulghum’s South American operations have been revised. Please refer to Note 2 in the Form 10-Q for the period ended March 31, 2015 for further explanation.

Three months ended March 31, 2015

Consolidated revenues for the first quarter of 2015 were $105.6 million, compared to $82.3 million in the prior year period. These revenues were comprised of:

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Gross profit for the first quarter of 2015 was $24.3 million, compared to $17.9 million in the prior year period. Gross profit was comprised of:

Consolidated Adjusted EBITDA for the first quarter of 2015 was $17.6 million, an improvement of $11.6 million compared to the prior year period. Consolidated Adjusted EBITDA included the following:

Further explanation of Adjusted EBITDA, a non-GAAP financial measure, as used here and throughout this press release, appears below.

Net loss attributable to Rentech common shareholders for the first quarter of 2015 was ($4.9) million, or ($0.02) per basic share, compared to a net loss of ($7.0) million, or a loss of ($0.03) per basic share, for the same period last year.

Fulghum Fibres

Revenues were $22.7 million for the first quarter of 2015, compared to $26.0 million for the same period last year. Revenues from operations in the U.S. were $13.6 million for the first quarter of 2015, as compared to $14.2 million in the prior year period. Volumes and revenues at a number of our U.S. mills were down due to wet and protracted winter weather. Revenues from operations in South America were $9.1 million for the first quarter of 2015, as compared to $11.8 million in the prior year period. The decrease in South American revenues was primarily due to lower biomass product sales domestically and to Asia in the first quarter of 2015 as compared to the first quarter of 2014. In addition, revenues from our South American processing mills were lower because of reduced volumes during the start-up of the new chipping line at our PAC mill, fibre transportation issues from our customer to our Valdivia mill, and discontinued services at the Los Sauces mill.

Fulghum’s mills in the U.S. and South America processed a total of 3.7 million green metric tons, or GMT, of logs into wood chips and residual fuels for the first quarter of 2015, compared to 3.8 million GMT in the first quarter last year.

Gross profit was $3.7 million for the first quarter of 2015, compared to $4.1 million for the same period last year. Gross profit margin for the first quarter of 2015 was 16%, which was essentially flat compared to the prior year period. The decrease in gross profit was primarily due to higher depreciation and amortization and to lower volumes processed and sold during the first quarter of 2015.

Adjusted EBITDA for the first quarter of 2015 was $4.0 million. This compares to Adjusted EBITDA of $4.5 million for the same period in 2014.

Net loss was ($1.1) million for the first quarter of 2015, compared to net income of $1.7 million for the same period last year.

New England Wood Pellet

Revenues were $12.1 million, including $1.2 million from the Allegheny mill, for the first quarter of 2015 on deliveries of 63,000 tons of wood pellets. Gross profit was $2.2 million and gross profit margin was 18%. Adjusted EBITDA was $2.3 million, and net income was $1.1 million.

Wood Pellets: Industrial

Revenues were $1.7 million for the Atikokan mill in the first quarter on deliveries of 9,100 metric tons of wood pellets to OPG. Gross loss was ($0.4) million and gross loss margin was (24%) due to operating at partial capacity at the Atikokan mill during commissioning.

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Adjusted EBITDA loss, including operating losses at the Wawa facility, business development for industrial wood pellets, senior management of the fibre business and corporate allocations, was ($3.9) million for the first quarter of 2015, compared to an Adjusted EBITDA loss of ($1.7) million for the same period in 2014. Net loss for the first quarter of 2015 was ($4.7) million, compared to a net loss of ($1.6) million for the same period in 2014.

Nitrogen Product Manufacturing

Revenues for the first quarter of 2015 were $69.2 million, compared to $56.3 million in the first quarter of 2014. Gross profit for the first quarter of 2015 was $18.8 million, compared to $13.8 million for the same period last year. Adjusted EBITDA for the first quarter of 2015 was $19.2 million, compared to $11.5 million in the corresponding 2014 period. Net income for the first quarter of 2015 was $9.0 million, compared to net income of $3.1 million for the prior year period.

East Dubuque Facility

Revenues for the first quarter of 2015 were $36.8 million, compared to $28.5 million for the same period last year. The increase was due to higher sales volumes for ammonia, partially offset by lower sales prices for ammonia and urea.

Ammonia deliveries increased due to strong demand from agricultural and industrial customers. Volumes were low in the first quarter of 2014 because production was interrupted by a planned turnaround and a fire in the fourth quarter of 2013, and production was purposely reduced in order to sell natural gas at high prices in the first quarter of 2014.

Average sales prices per ton for the first quarter of 2015 were 4% lower for ammonia and 1% higher for UAN, as compared with the same period last year. These two products comprised 78% of the East Dubuque facility’s revenues for the first quarter of 2015 and 58% for the same period last year.

Gross profit was $17.4 million for the first quarter of 2015; this compares to a gross profit of $12.4 million for the same period last year. Gross profit margin for the first quarter of 2015 was 47%, compared to 44% for the prior year period. Gross profit and margin benefited from higher sales volumes for ammonia and a $2.6 million unrealized gain on natural gas derivatives, partially offset by lower sales prices for ammonia and urea, lower natural gas sales, and increased labor costs and depreciation expense.

Adjusted EBITDA for the first quarter of 2015 was $19.3 million, compared to $13.5 million in the corresponding period in 2014.

Net income was $16.0 million for the first quarter of 2015, compared to $11.2 million for the same period last year.

Pasadena Facility

Revenues for the first quarter of 2015 were $32.4 million, compared to $27.8 million for the same period last year. The increase was due to higher sales prices for ammonium sulfate and sulfuric acid, and higher sales volumes for sulfuric acid, partially offset by lower sales volumes for ammonium sulfate and lower sales prices for ammonium thiosulfate.

Average sales prices per ton increased for ammonium sulfate by 28% and by 2% for sulfuric acid for the first quarter of 2015, as compared with the same period last year. Factors contributing to higher sales prices for ammonium sulfate include a larger proportion of higher-priced domestic sales and more favorable supply and demand conditions. Ammonium sulfate and sulfuric acid comprised 88% of the Pasadena facility’s revenues for the first quarter of 2015 and 83% for the same period last year.

Gross profit was $1.3 million for the first quarter of 2015, compared to $1.4 million for the same period last year. Gross profit margin for the first quarter of 2015 was 4%, compared to 5% for the same period last year.

Adjusted EBITDA for the first quarter of 2015 was $2.0 million, compared to $0.3 million in the corresponding period in 2014.

Net income was $0.2 million for the first quarter of 2015, compared to a net loss of $0.8 million for the same period last year.

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Corporate Unallocated Expenses

Corporate unallocated expenses, recorded as selling, general and administrative (SG&A) expenses, were $3.9 million for the first quarter of 2015, compared to $6.8 million in the corresponding period in 2014.

The table below provides a comparison of adjusted unallocated SG&A expenses for the first quarters of 2015 and 2014, including certain adjustments for comparability.

Conference Call with Management

The Company will hold a conference call today, May 11, 2015, at 8:30 a.m. PDT, during which Rentech’s senior management will review the Company’s financial results for this period and provide an update on corporate developments. Callers may listen to the live presentation, which will be followed by a question and answer segment, by dialing 888-517-2513 or 847-619-6533 and entering the pass code 7750504#. An audio webcast of the call will be available at www.rentechinc.com within the Investor Relations portion of the site, under the Presentations section. A replay will be available by audio webcast and teleconference from 11:00 a.m. PDT on May 11 through 11:59 a.m. PDT on May 18. The replay teleconference will be available by dialing 888-843-7419 or 630-652-3042 and entering the audience passcode 7750504#.

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Rentech, Inc.

Consolidated Statements of Operations

(Amounts in Thousands, Except per Share Data)

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Rentech, Inc.

Statements of Operation by Business Segment

(Stated in Thousands)

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Rentech, Inc.

Selected Balance Sheet Data

(Stated in Thousands)

Disclosure Regarding Non-GAAP Financial Measures

Rentech’s Adjusted EBITDA is defined as Rentech’s new income (loss) plus interest expense, income tax expense, depreciation and amortization. Rentech Nitrogen’s Adjusted EBITDA is defined as Rentech Nitrogen’s net income (loss) plus interest expense and other financing costs, income tax expense, depreciation and amortization. Fulghum’s Adjusted EBITDA is defined as Fulghum’s net income (loss) plus interest expense and other financing costs, depreciation and amortization, and income tax expense. NEWP’s Adjusted EBITDA is defined as NEWP’s net income plus interest expense and other financing costs, depreciation and amortization, and income tax expense. Wood Pellets: Industrial’s Adjusted EBITDA is defined as Wood Pellets: Industrial’s net loss plus interest expense, depreciation and amortization and income tax expense. Adjusted EBITDA is used as a supplemental financial measure by management and by external users of our consolidated financial statements, such as investors and commercial banks, to assess:

The non-GAAP financial measures described above are used as supplemental financial measures by management and by external users of our financial statements, such as investors and commercial banks, to assess:

These non-GAAP financial measures should not be considered an alternative to any measure of financial performance or liquidity presented in accordance with GAAP. These non-GAAP financial measures may have material limitations as performance measures because they exclude items that are necessary elements of our businesses’ costs and operations. In addition, EBITDA and Adjusted EBITDA presented by other companies may not be comparable to our presentation of those measures, since each company may define these terms differently.

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The table below reconciles Rentech’s consolidated Adjusted EBITDA to net income (loss) for the first quarter of 2015 and 2014. The consolidated Adjusted EBITDA includes Adjusted EBITDA from 100% of Rentech’s subsidiaries, most notably Rentech Nitrogen Partners.

The table below reconciles Rentech Nitrogen’s Adjusted EBITDA, along with the Adjusted EBITDA for each of its facilities, to their respective net income (loss) for the first quarter of 2015.

The table below reconciles Rentech Nitrogen’s consolidated Adjusted EBITDA, along with the Adjusted EBITDA for each of its facilities, to their respective net income (loss) for the first quarter of 2014.

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The table below reconciles Fulghum’s Adjusted EBITDA to net income (loss) for the first quarter of 2015 and 2014.

The table below reconciles NEWP’s Adjusted EBITDA to net income for the first quarter of 2015.

The table below reconciles Wood Pellets: Industrial’s Adjusted EBITDA to net loss for the first quarter of 2015.

About Rentech, Inc.

Rentech, Inc. (NASDAQ: RTK) owns and operates wood fibre processing, wood pellet production and nitrogen fertilizer manufacturing businesses. Rentech offers a full range of integrated wood fibre services for commercial and industrial customers around the world, including wood chipping services, operations, marketing, trading and vessel loading, through its subsidiary, Fulghum Fibres. The Company’s New England Wood Pellet subsidiary is a leading producer of bagged wood pellets for the U.S. heating market. Rentech manufactures and sells nitrogen fertilizer through its publicly-traded subsidiary, Rentech Nitrogen Partners, L.P. (NYSE: RNF). Please visit www.rentechinc.com and www.rentechnitrogen.com for more information.

Safe Harbor Statement

This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995 about matters such as the performance of our Canadian wood pellet plants. These statements are based on management’s current expectations and actual results may differ materially as a result of various risks and uncertainties. Other factors that could cause actual results to differ from those reflected in the forward-looking statements are set forth in the Company’s prior press releases and periodic public filings with the Securities and

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Exchange Commission, which are available via Rentech’s website at www.rentechinc.com. The forward-looking statements in this press release are made as of the date of this press release and Rentech does not undertake to revise or update these forward-looking statements, except to the extent that it is required to do so under applicable law.

Source: Rentech, Inc.

Rentech, Inc.

Julie Dawoodjee Cafarella

Vice president of Investor Relations and Communications

310-571-9800

ir@rentk.com

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