Come October it’s time to plant out local vegetable gardens, but for some leafy greens it is best to wait until the cooler weather of mid-November. Temperatures that are too high can interfere with germination of seeds, e.g., above 75ºF lettuce seeds become dormant. Some items such as collards, mustard greens and cabbage, where optimum germination requires warmer soil temperatures, can be planted earlier. However subsequent growth of these and the other commonly grown leafy greens requires cool temperatures, especially during their latter phase of growth before harvesting. Cabbages for instance will grow at temperatures as low as 42ºF, but cease growing above 76ºF. As temperature increase, most of these vegetables develop a more pronounced, bitter taste. For optimum quality this means setting out plants in Miami-Dade so that they reach maturity during the months from December to February.
Kale was until recently just another minor vegetable, but has recently risen to prominence as one of the most healthful and nutritious of all leafy greens. In Florida it has mostly been a backyard crop; the main problem is the short season as it is not suited to hot weather. Temperatures above 75°F will see a decline in quality with less compact leaves and increasing bitterness.
Closely related to cabbage, but with a shorter season (November to January), kale produces a rosette of leaves (usually curly) atop a thick stem. It requires a sunny site with moist, enriched but free draining soil. On sandy soil incorporate organic matter (compost, dried manure), while on bare Miami limestone a raised bed is recommended. Kale is quite salt tolerant so is a good choice for coastal gardens. It is usual to sow seeds directly (if preferred they can first be grown 3-4 weeks in advance as transplants); scatter a complete slow release vegetable fertilizer and irrigate to keep soil moist. Kale readily germinates (4-7 days) – as the plants grow thin out to a spacing of at least 12” between plants (thinnings can be consumed).
There is no precise time as to when to harvest kale – about 2 months from sowing seed, after which lower leaves can be consumed as they reach a suitable size, continuing until they become excessively bitter. Kale is not as troubled with pests as much as other leafy greens – leaf chewing caterpillars and cut worms are of principal concern.
Recommended varieties for Florida: Dwarf Blue, Curled Variety’s; Dwarf Siberian, Tuscan; Winterbor and Redbor.
Spinach is not an important commercial crop in Florida; again the main constraint is climate. Spinach seed germination is poor at temperature above 77°F; subsequent growth is optimum at 68°F. With increasing day length and temperatures above 75°F spinach becomes more likely to bolt (flowering is initiated at which time vegetative growth stops, the plant flowers and goes to seed).
The planting area should be in full sun; like kale, spinach is quite tolerant of saline soils (it also adapts to high pH soils). The area should also be free of weeds – weedy relatives of spinach (e.g., pigweed) can harbor diseases and insect pests. Seed should be sown November to January using fresh, moist but free draining soil - excessive water can promote damping-off of emerging seedlings due to fungi (Pythium, Rhizoctonia and Fusarium), especially in warm weather. Spinach is very susceptible to both damping off and root rots; these can be severe problems particularly in Florida.
Expect seed germination after 10 days; plants should be spaced 5” apart, 15” between rows. Spinach has a shallow root system so it will require reliable irrigation – if hand watering, keep water off the leaves to help prevent disease especially downy mildew and white rust. Provide a light application of slow release vegetable fertilizer. Apart from diseases, leaf chewing insects can be a problem (various caterpillars); also look for damage due to cut worms, leaf miners and aphids. Careful application of mulch in between spinach plants can reduce weed growth.
Under local conditions it usually takes 6-8 weeks until harvest - the whole plant can be removed or a few leaves at a time over a period of 2-3 weeks. Once signs of a flowering stem are seen the whole plant should be removed. Baby spinach, which is popular in salads, is harvested as soon as 3-4 weeks after planting.
Recommended varieties for Florida: Virginia Savoy; Dixie Market; Hybrid 7, Regiment-F1 and Renegrade-F1 are claimed to resist bolting.
Cabbage is an important crop in Florida (principal production in Flagler and St Johns counties) though it is grown elsewhere within the state.
The earliest cultivated cabbages produced an open whorl of leaves, not the compact head we are familiar with today, and are referred to as non-heading cabbages. Collards, which are easy to grow, are sometimes referred to as a non-heading cabbage. The hard heading (occasionally called white) cabbages were developed later in cooler parts of Europe. The original types formed a rounded tight head of leaves, but later forms had flat, elongated, egg shaped or conical heads. Due to local mild winters, hard heading cabbages often do not develop a tight compact head; they can still be grown and leaves removed as required for consumption. Still later came a group of looser heading cabbages with a milder flavor and crinkled leaves, the Savoys.
Cabbage seed can be directly sown in the ground or used for transplants with a spacing of about 18” between plants and 30” between rows. Ideally they should receive 6 hours of sun per day but if necessary can take some limited part shade. Provide moist, enriched but free draining soil and fertilize with a slow release vegetable fertilizer.
Recommended varieties for Florida: Gourmet, King Cole, Rio Verde Savoy Ace and Chieftain Savoy.
Lettuce is not a major crop in Florida – the main growing area consists of a few large farms around Lake Okeechobee. There are four main types of lettuce: crisphead (iceberg - the type most often seen in produce stands), romaine (cos), butterhead (Boston) and loose leaf. Crisphead lettuce is not recommended since it requires a prolonged period of cool weather in order to develop a full tight head. Leaf lettuce (shown below) is the most heat tolerant and easiest to grow.
Choose a site that receives at least 6 hours of sun per day, and enrich soil with organic matter (only use manure that has been thoroughly composted i.e., dried and bagged). If you grow from seed avoid high soil temperatures (induces seed dormancy)) and barely cover the seeds with soil - lettuce seed requires light to germinate. If you wish you can grow transplants rather than seeding directly (it is easier to space out plants); many gardeners find it easier to purchase transplants from a garden center. Leave 8-12” between plants and 20” between rows.
It is important to irrigate lettuce as soon as the top of the soil appears to be drying-out (mulch will help to retain soil moisture) and apply a slow release vegetable fertilizer. Leaf lettuce should be ready after 45 days (transplants) and leaves can be removed as needed Romaine will require at least 65 days and leaves can be removed or the whole head. Romaine lettuce is popular with local gardeners, though it develops a stronger flavor and tougher leaves with warming temperatures of early spring.
The principal pests of lettuce are various caterpillars including cutworms, aphids and to a lesser extent leaf miners and cucumber beetles. Root nematodes can be a serious pest of lettuce; on sandy soil in particular mulching and enriching the soil with organic matter can help control this problem.
Recommended varieties for Florida: leaf lettuce - varieties such as Prize Head, Salad Bowl, and Cocarde; Romaine lettuce - Parris Island Cos, Jericho (especially heat tolerant) and Valmaine.
Reprinted from Miami Green Bytes, Fall 2013
Article by Dr. John McLaughlin
To see the entire Fall 2013 issue of Miami Green Bytes click here.