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Friday, April 15, 2011

Harvesting Herbs and Easily Damaged Vegetables

Basil Growing in the hot Las Vegas Valley of the Mojave Desert

Nothing is worse than harvesting herbs and eggplant and by the time you get them in the door they are withered or soft and no longer firm. Or your products didn’t last very long in their cooler. Here are some suggestions on how to harvest these tender plants from the garden and keep them fresh.

The ideal time to harvest most herbs is as early in the morning as possible. This is the time of day when temperatures are lowest, humidity is highest and winds are low. This is also the time for herbs when those volatile oils that are so important are at their peak and flavors are best. Harvesting should be at a time when the flower buds are just starting to form but before they open. When the flowering cycle begins, the plant begins to shove nutrients at the flowers and subsequent seeds which takes precedence over the production of leaves and stems. Flower formation indicates this loss of nutrients in leaves and stems is about to happen. After some familiarity you will begin to visually predict when this occurs as you note changes in the growth of the plant.

If at all possible, spray herbs and soft vegetables with a mist of water 10 to 20 minutes before harvesting to wash dirt from the surface, cool the plant down and rehydrate the surface. Check with your local ordinances to make sure this is permissable prior to sale if you are selling. In the case of vegetables, the larger the vegetables the longer it takes to cool the plant down. So don’t expect that a quick rinse of eggplant for instance to have much impact in cooling the fruit down internally. In our dry climate the cooling effect from spraying a plant down with water may last ten minutes at best and then the temperature begins to climb back toward the air temperature quickly. On the contrary, a light mist of water on the surface of most delicate herbs and leafy vegetables will cool the plants down considerably.

Make sure you take a clean bucket with cool, clean water (nonchlorinated would be best) into the field with you. During summer months the water temperature should be at least cool to the touch and cooler than the air temperature. For those requiring more exacting guidelines you should have temperatures about 55 to 65 F. There are some plants that can be packed in ice while others cannot. Icing is usually reserved for cold hardier plants like broccoli, spinach, cilantro, parsley, green onions, and Brussels sprouts. Icing more tender plants will result in injury.

The four major enemies to plant quality and storage life occur after harvest: damage from handling, low humidity and water loss, high temperatures, and direct sunlight. Do everything you can to keep these enemies from damaging your harvest.

Damage from handling. Harvesting requires a sharp and sterile knife or shears. Herbs and soft vegetables should be severed from the plant cleanly without tearing or ripping and lifted rather than pulled and immediately immersed in clean, cool water. Any surface tearing or scarring impacts the quality of herbs and soft vegetables and their storage life. If you have long fingernails or wear jewelry on your hands that could tear or rip, wear thin plastic gloves to protect these tender plant parts from damage. This may sound like these precautions are “overboard” but if you expect to store these plant parts for any length of time, damage to the surface of the plant allows water to be lost and disease pathogens entrance. All herbs and soft vegetables have to be inspected for damage and sorted for quality. Sorting or grading of products, if not done carefully and out of harsh conditions, can intensify damage and result in even more losses.

Low humidity and water loss. Our desert climate is naturally low in humidity. That is great for growing plants but not so after harvesting. As soon as the herbs or vegetables are severed from the plant its source of water is removed, air enters the stems, water no longer moves through the severed plant part. Plants with roots attached can lose water from leaf and stem surfaces and water from the roots replenishes lost water. This keeps the leaves and stems hydrated and cool. Evaporation of water from leaves and stems helps cool the plant. As water is lost from severed plant parts their freshness and quality is compromised. Immersing them in cool, clean water immediately after harvest helps keep these products hydrated and fresh. Keep these plant parts out of the wind, direct sunlight and high temperatures which drive excessive water loss.

High temperatures. It should go without much explanation that harvested plant parts should be kept cool unless you are dealing with vegetables that require high temperature and humidity after harvest such as sweet potatoes.

Direct sunlight. The energy from the sun can be deceivingly destructive. I don’t know how many times I have told people in the field to put harvested products in the shade, even if it is under the shade of other plants. This is one of the most commonly abused practices after harvest. I observed small-scale producers in Kenya on the slopes of Mt. Kenya harvesting products and putting them in direct sunlight to be picked up by the co-op truck a few hours later. To top it all, these products were sorted and graded at the co-op headquarters by co-op members in DIRECT SUNLIGHT! Coop members then did not understand why half or more of their harvest was rejected by the exporter.

Cleaning. A light salt solution (two tbs per five gallons or 35 g. per 20 L) can clean products of insects without damaging plant parts. Straight table salt, sodium chloride, has two chemicals that can cause plant damage; sodium and chloride ions. If too intense, damage will result. A better salt might be a potassium based salt rather than sodium which can be very toxic to plants. Immerse the plant parts in salt water, remove and dry in a salad spinner and place in a sealed container with a sterile, wet blotter and in a cool location out of direct sunlight. Herbs can be dried completely by blotting with paper or soft towels.

Storage. Storage temperatures for most herbs is close to freezing but not below freezing and humidity as close to 100% as possible. Refrigeration (41F or 5C) is next best loses about one week of storage life compared to near freezing. Freezing damage appears as darkened translucent or water-soaked areas. These areas deteriorate and wilt rapidly after bringing to room temperature and ruins the product. Expected shelf-life is 3 weeks at near freezing (32F or 0C) and 2 weeks at 41°F or 5C. http://postharvest.ucdavis.edu/Produce/ProduceFacts/Veg/herbs.shtml.

I have noted shelf life longer than this in locally grown products when handled correctly.

Were You Ever Called a Manipulator?

USON Faculty with Bob Morris and selections of nopal cactus from Sonora, Mexico.

Horticulture is the manipulation of plants to get them to do what we want them to do. A basic horticultural premise that I operate from is the concept that as we deviate in our plant selection further and further from those plants which are desert adapted, the more time, energy and money we must devote to their care. There is nothing wrong with that. But it becomes a problem when we don’t realize it and we expect any plant that we put in our soil to behave the same way as any other plant. We also don’t realize that these “out of place” plants require more of our time, energy and money to perform well.

Then Maybe You Should Take Up Horticulture!

Growing nopal cactus here requires much less effort than growing tomatoes, a tropical plant. Much more care is required of that tomato plant to get it to do what we want it to do than it does to grow that cactus. The problem becomes “What exactly does that tomato require to get it to perform to its maximum?” The cactus will perform to its maximum, growing and fresh vegetable and fruits, with less expenditure of time, energy and money.

Horticulture is simply the manipulation of plant traits (characteristics like size, shape, leaf and flower color, etc.) for hobby, profit or curiosity. The other sciences of growing plants like agriculture and botany, are less focused on plant manipulation than in horticulture. Those of us who call ourselves horticulturists enjoy or make money from our abilities to manipulate plants, getting them to do what we want them to do. To learn this requires patience, a basic understanding of plants, soils, weather and climate, water and irrigation, careful observation of plants, and acquired skills. Because of this, frequently horticulture is considered an “art” or skill as much as a science. But good horticulturists can get plants to do what no other plant scientist can and that is to respond to our needs and wants.

Our climate is considered a desert climate. Deserts have been defined as those climates with ten inches or less rainfall each year. Arid climates are more general in nature and typically meaning that they are incapable of supporting some form of agriculture without supplemental irrigation. Because we live in the middle elevations of the Mojave Desert (2000 foot elevation) and we have distinctive seasons, our climate could be considered a temperate desert climate.

We enjoy many different types of landscape plants that originate from various climates all over the world; cold northern climates, hot tropical climates, wet Marine type climates, Mediterranean climates, and others. When we select plants that originate from climates that are different from ours, these plants may behave differently when planted here and the management of them must reflect these differences and compensate for them.