Organic Vegetable Gardening in the Desert

Organic Vegetable Gardening in the Desert Joran Viers Bernalillo County Cooperative Extension Service Albuquerque, New Mexico “Organic” defined • To chemists: simply describes fact of carbon backbone to molecules: natural and synthetic organic compounds exist. • To gardeners: implies a perspective favoring natural sources for soil fertility, and natural methods and materials for pest control. To some there is a “spiritual” component as well. • Commercial agriculture: process-based production system utilizing natural materials, and requiring much paperwork and verification. Perspective • Adherence to principle of “feed the soil” – compost, manure, green manures, etc. • Natural pest control: cultural/physical changes to make habitat better for plants; use of resistant varieties (but not GMO); judicious application of pest control materials; acceptance of certain level of imperfection as indicator of “purity”. Perspective • Basic issues remain: – Soil types and their characteristics; – Climatic conditions (rainfall, temperature, etc.); – Common pests (insects, weeds, diseases); – Soil fertility: plants need certain minerals in soil in order to grow well; – Species/variety likes/dislikes. Feed the Soil • Plants evolved getting nutrients from soil – either mineral or from organic matter. Soil fauna is essential to this process; • Plants don’t require a season’s worth of nutrients all at once; • Synthetic fertilizers are typically salts, which dissolve rapidly in soil solution – Can aggravate a soil salinity problem; – Nutrients may be lost before plants use them; – Nutrient level fluctuation can negatively affect soil microbial ecosystem. Synthetic Fertilizers • Some (how many?) commercial synthetic fertilizers use slag and other industrial wastes as “inert carriers” – Cases of farmers ruining fields for the foreseeable future by application of recommended rates of fertilizers. – Heavy metals are the concern – accumulation on farm/garden soils and the plants grown in them. The Soil • Mineral classification based on particle size: sand, loam, clay. • Parent material affects particle size, as well as: – pH: measure of alkalinity (acidity) of soil; most SW soils are pH > 7. – Buffering capacity: high lime content makes changing pH next to impossible. – Salinity, CEC, mineral nutrient levels… The Soil • Organic matter: humus – Typically low levels in our soils; – Has major impact on water and nutrient retention/release properties; – Needs to be replenished periodically (photoand biotic degradation); – Not all OM is created equal; will vary in nutrient levels, saltiness, pH, degree of decomposition,… Soil Preparation • Wide-bed planting: – Reduces non-crop area relative to crop yield; – Reduces labor associated with spread-out gardens; – Plants are somewhat self-mulching; – Allows for intensive soil loosening prep work (double-digging); – Easily accommodates drip irrigation. • Add in compost or other OM and any mineral nutrients at time of double-digging. Excerpted from: How to Grow More Vegetables…, by John Jeavons. Soil Building • Organic Matter: – Compost: intentionally decomposed plant and animal remains; rich earthy smell, dark brown and crumbly. Use to enrich soil, as top-dress/mulch, in making planting mixes. Moderate N level, good balance of all plant nutrients. – Manure: un-decomposed animal manure; may be easily available; give it time to decompose in soil; be aware of salt buildup potential. Higher N level. – Green manure: crop (often legume) grown to be returned to soil; adds bulk carbon, may add nitrogen; feeds soil ecosystem; least loss. – Leaves, grass clippings, etc.: can have a place, but be aware of limitations (high carbon, matting, etc.). Compost • Requires right mix of dry (brown) and fresh (green, or manure) materials; C:N between 25:1 and 35:1. • Pile should be at least 3x3x3 to heat up properly. • Turn after temperature comes down. • Keep moist; cover if necessary. • Use a multiple bin system for easy turning. Common Compost Problems* Problem • Wet, foul-smelling pile Remedy • Turn pile, add high-carbon material • Turn pile, soaking thoroughly; cover with plastic to retain moisture • Increase volume of pile and moisten well • Add nitrogen-rich materials, turn • Break up layers, or shred, relayer pile; avoid adding these materials in heavy layers • Screen out un-decomposed items and use in next pile • Dry center and little or no decomposition of materials • Dampness and warmth only in middle • Damp, sweet-smelling but no heat • Matted, un-decomposed layers of leaves, paper or grass clippings • Large un-decomposed items *Taken from The Rodale Book of Composting You may need to add… • Nitrogen: blood meal, fish emulsion, manure tea, alfalfa mulch (SLOW release); • Phosphorus: bone meal, rock phosphate; due to high pH, may very quickly become unavailable – mix 50:50 with elemental sulfur at application; • Potassium: greensand (also has micronutrients) • Micronutrients: often in soil but unavailable, so adding S can help (how much and when?); • Humates offer an unknown level of benefit; humic and fulvic acids, long-term stability. Crop rotation limits pest/disease buildup, may improve soil. Based on plant families and cultivation requirements. • Solanaceae: tomato, potato, eggplant, pepper. • Brassicaceae: cabbage, broccoli, kale, turnip, mustard, etc. • Cucurbitaceae: squash, melon, cucumber. • Poaceae: corn, wheat, barley, rye • Fabaceae: bean, pea, medic, vetch, etc. • Apiaceae: carrot, parsley, cilantro, fennel. • Liliaceae: onion, garlic, leeks, chives, asparagus. Soil Solarization: • Till soil, wet up real well; • Cover with heavy-duty clear plastic, anchored along all edges; • Leave in the sun for several weeks to heat sterilize upper inches. • Kills insects, eggs, seeds in the heated soil. Direct seeding or transplanting? • Some plants don’t take transplanting well (cucurbits, root crops, beans and peas). • Some do (tomato, pepper, eggplant, greens of all types, early corn). • All plants that transplant well do just as well direct seeded. • Can gain a week or two, depending on soil temperatures. • Cost, hassle trade-offs. • May help get ahead of weed problems. Seeders for large areas. Pest Control • Pests include: – – – – Weeds Insects Larger animals Diseases Weeds • Annual weeds: – Cultivate before new seed set; – Smother with mulch (before or after weed seedling emergence); – Use corn gluten meal as a pre-emergent herbicide that breaks down into a 12%+ N source; – Flame weeding can work well but BE CAREFUL especially during the current drought. Kochia scoparia Cultivation tools come in all sizes and shapes. Perennial Weeds • Harder to control, as a rule; • Mulching can help; • Repeated cultivation and/or flaming can help; • For bindweed: bindweed gall mite; • Crop rotation, green manuring, etc. can help. Silverleaf nightshade and buffalo bur are both relatives of tomato, potato, pepper. Both have spines and irritating chemistry. Common mallow (cheese weed) and spurred anoda are both relatives of cotton, hibiscus. Both are common agricultural weeds. • In general: – Young weeds are easier to control by whatever method. – Weeds can be composted, or used for mulch, if they haven’t set seed. – If they have set seed, dispose of by burning, burying, or similar solution. – Soil solarization can kill weeds and seeds at the soil surface. – Some weeds can harbor diseases (London rocket and beet curly top virus). Insects • Both pests and allies. – Most lepidopterans are pests (as larva); – Many hemipterans are pests but some are predators; – Many homopterans are pests; – Most hymenopterans are allies. – Coleopterans are found in both categories. • It pays to know your bugs! Lepidopterans = moths and butterflies Tomato hornworm Painted lady Corn earworm • Bacillus thurengiensis a.k.a. Bt is a bacteriabased stomach poison specific to lepidopteran larva. Apply at first sign of activity, re-apply as needed. • Vegetable oil plus pyrethrum on corn silk. • Handpick the big ones and feed to the hens. Hemipterans = true bugs • Squash bugs: – Plant late, plant often; – Row covers until bloom; – Rotenone on very young nymphs; – Trap cropping; – Flaming; – Disguise with buffalo gourd. • Treat harlequin bugs with pyrethrum. Predator Bugs Damsel bug Big-eyed bug Assassin bug nymphs Homopterans = aphids & their ilk • Aphids: – Do nothing: let the beneficials find them and establish their own populations; – Wash off with strong jet of water; – Treat with insecticidal soap; – Beauveria bassiana fungal product; – Neem, pyrethrum, etc. Hymenopterans = wasp, bees, ants • Larger wasps often caterpillar predators; • Smaller wasps often parasitoids of eggs and larva; • Bees are key pollinators; • Ants are a mixed bag – can farm aphids, can also help build soils and control some pests. Coleopterans = beetles • Ladybugs, ground beetles, tiger beetles are all good predators. • Weevils, Mexican bean beetles, flea beetles are pests. – Bt specific to Colorado potato beetle: variety tenebrionis Green June beetles are opportunistic feeders. For beetle control, try: Neem, pyrethrum, rotenone, Sharpshooter ™ citric acid insecticide, homemade tobacco extract. Mexican bean beetle damage, adult and larva. Insect Repellants • Purchased or homemade extracts of certain plants may deter pests. – Garlic – Hot pepper – Tobacco Insect Attractants • Pheromone traps to control codling moth – Traps alone for small home orchards of a few trees; – Traps plus selective sprays (Kocide, spinosad, Bt) to control; – Pheromone alone for large-scale mating disruption. Small-flowered plants attract adults of many beneficial insects due to nectar. Plant along borders, etc. Got snails? Get turtles! Diseases Our dry climate suppresses many fungal and bacterial disease organisms. Good garden sanitation will help a lot, also. Sulfur, neem, copper products, jojoba oil (for powdery mildew and whiteflies). Curly top virus affects many plants including squash. Beet leaf hopper is the vector, winter annual mustards an alternate host. Prevention!!! Resources • Books: – How to Grow More Food…, by John Jeavons. – The New Organic Grower, by Eliot Coleman. – Most anything by Rodale Press • Other media: – Peaceful Valley Farm Supply catalog (www.groworganic.com). – ATTRA (www.attra.org) – Cooperative Extension Service offices – Knowledgeable local gardeners.