Gardening in New Mexico: zones, frost dates and when to plant

Elevation sets the season

New Mexico takes in mountains, forests, grasslands and desert, and the growing season follows elevation more than latitude. NOAA’s climate summary puts the northern mountains in the low 20s °F in January and around 60°F in July, while the low southern valleys run from the mid 40s to the low 80s. Higher ground generally means a shorter season.

NMSU Extension’s Home Vegetable Gardening in New Mexico (Circular 457) uses two towns to show the spread. Okra and watermelon struggle to mature in short-season places like Los Alamos, while kale does poorly in the summer heat of Roswell. Its companion, Circular 457-B, groups planting dates into three bands of growing zones and notes that warmer areas often get both a spring and a fall window for many crops. Colder areas with fewer frost-free days need long-season crops started indoors as transplants.

Your own yard can differ from the regional average by as much as 20 days. Cold air drains downhill, so a garden on the valley floor stays colder in spring than one on the slope above it. A south-facing site warms sooner than a north-facing one. Use the frost dates for your city above as a starting point, then adjust for where your garden sits.

Water, soil and wind

Most of the state is arid to semiarid. NOAA notes that much of central and western New Mexico gets less than 15 inches of precipitation a year. The North American Monsoon, which can begin in late June and run into September, makes July and August the wettest months across much of the state, but monsoon totals swing widely from year to year.

NMSU’s advice on watering is specific:

• Keep soil moist until seeds germinate and plants establish.
• After that, water deeply, wetting the soil at least 12 inches down, and let the top ½ to 1 inch dry between irrigations.
• Sandy soils may need water every 3 to 7 days; heavier soils every 8 to 12 days, more often in hot weather.
• Drip irrigation is the most efficient method. Like furrow irrigation, it pushes salts away from the plants, but you may need an occasional flood irrigation to move built-up salts deeper.
• If you use sprinklers, run them in the morning. Late-day sprinkling raises the risk of powdery mildew, and a lot of water is lost on windy days.

New Mexico soils are mostly alkaline and low in organic matter. At high pH, phosphorus, iron and zinc become harder for plants to take up. NMSU recommends working in 1 to 2 inches of well-decomposed compost, which also improves water holding in sand and drainage in clay. Watch for hardpans and caliche near the surface. If you can’t fix the drainage, use raised beds. Plant windbreaks such as trees, fences or walls a safe distance southwest of the garden to shelter seedlings from spring winds.

Working with microclimates

Circular 457 suggests using your site’s warm and cool spots. Watermelons planted against a south-facing block wall get extra heat from the masonry at night, and leaf lettuce on the shady north side of a house lasts later into spring. Black plastic mulch warms the soil early for tomatoes and melons. Organic mulches such as weed-free straw keep the soil cool around cool-season crops. Water-filled plastic sleeves, hot caps and row covers help in early spring.

Tomatoes are the most popular home crop in the state, but they set fruit poorly when nights fall below 55°F or days climb above 95°F. NMSU recommends transplants at higher elevations, where the season is short, and says tomatoes can be direct-seeded in central and southern New Mexico. Heat-tolerant varieties make sense in the warmer areas. For onions, match day length to your location. Growing onions from seed is mostly done in the south.

Chile and other local crops

NMSU’s Growing Chile Peppers in New Mexico Gardens (Guide H-240) recommends transplants for most gardens, with direct seeding only where the season is long. Chile prefers well-drained loam or sandy loam with a pH of 7.0 to 8.5. Fruit set is best with days of 65 to 85°F and nights of 60 to 70°F. Black plastic helps warm the soil early, especially in northern New Mexico, and can be swapped for straw once summer heat arrives. Row covers early in the season keep out the beet leafhopper, which spreads curly top. Drip irrigation and raised beds reduce Phytophthora root rot, also known as chile wilt. For bell peppers, the guide recommends ‘Jupiter’, ‘Keystone Resistant Giant’, ‘Bell Boy’, ‘Gypsy Hybrid’ and ‘California Wonder’.

Circular 457 also mentions crops with local followings. The Aztec bean, a vigorous climber, has become popular in northern New Mexico gardens. Lemon cucumbers are a common choice statewide. Rhubarb does well in the cooler parts of the state but has not succeeded in the warmer south.

Soil testing

NMSU advises basing fertilizer on a soil test and contacting your county Extension agent for help. Guide A-114, Test Your Garden Soil, explains how to take a composite sample from five or six spots in a garden. It also warns that home test kits overstate phosphorus in high-pH soils. Without a test, Circular 457 suggests a complete fertilizer relatively high in phosphorus, such as 5-10-5, worked into the soil before planting.