Gordon Johnson, Extension Vegetable & Fruit Specialist; email@example.com
Fall vegetable harvest will begin soon. For best quality and longevity of leafy and heading crops in the fall, it is important to reduce respiration and water loss from crops immediately after harvest. Harvest is best done in the early morning when field heat is lowest. All of these crops are best stored at near freezing and high humidity.
Broccoli should be harvested when heads have reached maximum diameter and flower buds (beads) are still tight. Bunched broccoli heads are tied together in groups of 3-4 with a rubber band. Broccoli should be hydrocooled or packed in ice immediately after harvest and stored at 32°F (0°C) and relative humidity of 95-100% to maintain salable condition. Under these conditions broccoli should keep satisfactorily 10-14 days.
Cabbage is harvested when heads are tight and have reached the desired size for the variety and spacing. The head is harvested by bending it to one side and cutting the base with a knife. Harvesting knives should be sharpened frequently. The stalk should be cut flat and as close to the head as possible, yet long enough to retain 2-4 wrapper leaves. Extra leaves leaves should be removed. Heads with insect damage and other defects should be discarded. Room or forced air cool harvested cabbage and then store at 32°F (0°C) and a relative humidity of 98-100%. Barrel-type Chinese cabbage (Napa cabbage) is handled similarly but is more fragile and requires a large twist-tie to keep leaves tight.
Cauliflower is harvested while the heads are pure white and before the curds become loose. Most varieties are self-blanching. For those that are not, blanching is achieved by tying outer leaves over the heads when heads are 3 to 4 inches in diameter. Blanching takes about 1 week in hot weather and 2 weeks in cooler weather. The head is harvested by bending it to one side and cutting the base with a knife. Harvesting knives should be sharpened frequently. The stalk should be cut flat and as close to the head as possible with a minimum of wrapper leaves. Cauliflower may cut, wrapped, and packed in the field. Reduce temperatures using room cooling or forced air. Store harvested cauliflower at 32°F (0°C) and a relative humidity of at least 95%. Avoid bruising heads in harvest, handling and packing.
Brussels sprouts are the compact vegetative buds that develop along the stem of the Brussels sprouts plant. They should be harvested when the buds are firm, but not overmature which is indicated by splitting of the outer leaves. Harvest by snapping and trim with a sharp knife. Good quality Brussels sprouts should be bright green, without yellowing or discoloration, and have a firm texture. Brussels sprouts are moderately perishable and can be stored 3-5 weeks at temperatures near the optimum of 0°C (32°F) and 95% relative humidity. Brussels sprouts are often hydrocooled, but can be force air cooled as well.
Kale and Collards may be harvested by cutting off entire plants near ground level. Whole plants are then bunched. As an alternative, lower leaves may be stripped from plants and packed individually. Kale and collards may also be machine cut 4-6 inches from the ground when full tonnage has been achieved but before petioles have elongated. Multiple harvests are possible. Because of their perishability, kale and collards should be held as close to 32°F (0°C) as possible. At this temperature, they can be held for 10-14 days. Relative humidity of at least 95% is desirable to prevent wilting. Air circulation should be adequate to remove heat of respiration, but excessive air circulation will speed transpiration and wilting. Satisfactory precooling is accomplished by vacuum cooling or hydrocooling. These leafy greens are commonly shipped with package and top ice to maintain freshness. Kale packed in polyethylene lined crates and protected by crushed ice keeps in excellent condition for 3 weeks at 32°F (0°C).
Lettuce is extremely perishable and needs to be handled delicately and marketed rapidly. Head lettuce is harvested when the heads are of good size (about 2 lb) and solid. Head lettuce is hand cut and trimmed (leave 3 undamaged wrapper leaves on each head) and placed in containers in the field. It is then vacuum cooled or hydrocooled. Specialty leaf lettuces and other greens for bag mixes are harvested by hand or mechanically. Leaf, butterhead and cos/romaine types are cut and trimmed in the field. Lettuce should be precooled to 34°F (1°C) by hydrocooling soon after harvest and stored at 32°F (0°C) and 98-100% relative humidity for retention of quality and shelf life. At 32°F, head lettuce can be held in good condition for 2-3 weeks. Leaf, cos/romaine, and butterhead lettuce have a shorter shelf life. Lettuce is easily damaged by freezing, so all parts of the storage room must be kept above the freezing point (31.7°F, -0.2°C).
Turnip and Mustard Greens for baby salad mixes are cut at ground level for a single harvest, or 1-2 inches from the ground for multiple cuts. Larger turnip, mustard, and Asian greens may be harvested by cutting off entire plants near ground level for a single harvest, or by cutting 2-6 inches above the ground to allow for regrowth. For processing, greens are machine cut 4-6 inches from the ground when full tonnage has been achieved but before petioles and midribs have become too large. Multiple harvests may be possible. Greens should be transported as quickly as possible to the packing area. Hydrocooling or vacuum cooling are recommended for pre-cooling. Greens should be held as close to 32°F as possible, because of their perishability. At this temperature, greens can be held 10-14 days. Relative humidity of at least 95% is desirable to prevent wilting. Air circulation should be adequate to remove heat of respiration, but not too rapid to speed transpiration and wilting. Greens are commonly shipped with plastic package and top ice. Greens packed in polyethylene-lined crates and protected by crushed ice keep in excellent condition if kept near 32°F but deteriorate rapidly at higher temperatures.
For fresh market Spinach, Chard, and Beet Tops, plants should be dry prior to harvest to prevent petiole breakage. When harvesting by hand, cut leaves above the crown or soil line and bunch. Exclude yellow leaves and leaves that are dirty with soil. Bunched spinach, chard, and beet tops must be handled very carefully to avoid breakage of plants or bunches during bunching, washing and packaging. Spinach for bag mixes are usually hand harvested, but mechanical harvesters for this purpose are now available. Walk-behind harvesters are also available for smaller acreage growers. Spinach, chard, and beet tops are very perishable and can be stored for only 10-14 days. Crushed ice should be used for rapid cooling and for removing the heat of respiration. Top ice, hydro-cooling and vacuum cooling are other satisfactory cooling methods. Store spinach at 32°F (0°C) and 95-100% relative humidity. Most spinach for fresh market is prepackaged in perforated plastic bags to reduce moisture loss and physical injury. Controlled atmospheres with 10-40% carbon dioxide and 10% oxygen retard yellowing and extend shelf life.
Maturity of Green Onions is determined primarily by size which is largely determined by seeding density. Green or “bunching” onions are selected varieties of white onion (Allium cepa) planted at high density or from the non-bulbing onion group (Allium fistulosum) generally called Japanese-bunching. Harvest when the onions are at ¼ to ½ inch in diameter at the base plate of the immature bulb or shank. Quality green onions have a thin, white shank or neck at least 5 to 7.5 cm (2-3 inches) in length. Green onions are highly perishable and normally marketed over a short period. Lowering and removing the heat of respiration as well as preventing water loss is critical. Package-icing and perforated polyethylene film liners are used cool quickly and maintain quality. Green onions may also be hydrocooled. Green onions are best held at 32°F and 98% humidity. Under these conditions they will store for up to 4 weeks.