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(1) Background: Winter grazing of livestock poses significant environmental risks of nitrogen (N) leaching and sediment runoff. (2) Methods: A field study tested the effects of sowing catch crops of oats (<i>Avena sativa</i> L.), ryecorn (<i>Secale cereale</i> L.) or triticale (<i>Triticosecale</i>) in June and August (winter) in Southland, New Zealand (NZ), on the risk of N leaching losses from simulated N loads left after winter forage grazing. (3) Results: Catch crops took up 141–191 kg N ha⁻¹ by green-chop silage maturity (approximately Zadoks growth stage 52; November/December). Importantly, early-sown catch crops were able to capture more N during the key leaching period from winter to mid-spring (77–106 kg N ha⁻¹ cf. 27–31 kg N ha⁻¹ for June and August treatments, respectively). At this time, ryecorn and triticale crops sown in June captured 20–29 kg ha⁻¹ more N than June-sown oats (77 kg N ha⁻¹). In October, early-sown catch crops reduced mineral N in the soil profile (0–45 cm depth) by 69–141 kg N ha⁻¹ through the process of plant uptake. At green-chop silage maturity, catch crop yields ranged from 6.6 to 14.6 t DM ha⁻¹. Highest yields and crop quality profiles (e.g., metabolizable energy, crude protein, soluble sugars and starch) were achieved by the oats, irrespective of the sowing date, indicating that trade-offs likely exist between environmental and productive performances of the catch crop species tested. (4) Conclusion: The catch crop of choice by farmers will depend on the desired end use for the crop, its place in the crop rotation and its potential for an environmental benefit.