Lettuce varieties will cross with each other, making spacing of 5 to 20 feet (1.5 to 6.1 m) between varieties necessary to prevent contamination when saving seeds. Lettuce will also cross with Lactuca serriola (wild lettuce), with the resulting seeds often producing a plant with tough, bitter leaves. Celtuce, a lettuce variety grown primarily in Asia for its stems, crosses easily with lettuces grown for their leaves. This propensity for crossing, however, has led to breeding programs using closely related species in Lactuca, such as L. serriola, L. saligna, and L. virosa, to broaden the available gene pool. Starting in the 1990s, such programs began to include more distantly related species such as L. tatarica. Seeds keep best when stored in cool conditions, and, unless stored cryogenically, remain viable the longest when stored at −4 °F (−20 °C); they are relatively short lived in storage. At room temperature, lettuce seeds remain viable for only a few months. However, when newly harvested lettuce seed is stored cryogenically, this life increases to a half-life of 500 years for vaporized nitrogen and 3,400 years for liquid nitrogen; this advantage is lost if seeds are not frozen promptly after harvesting.
Lettuce seeds can be harvested from your lettuce crop, but according to the University of Illinois, they do not keep well and are more difficult to germinate than seeds purchased in the spring. If you decide to harvest your lettuce seeds, plant them in the spring so if they do not grow as expected, you still have time to buy other seeds and plant them during the same season.
comment – you have to think if this makes sense. in fact it makes sense, it is just that you need to learn what is the lesson you can derive from this practice. here are a few points about this recommendation –
- it assumes it is planted in a typical gound that goes thruogh the normal seasonal cycle – spring, summer, and autumn. it suggests to be a good seed, it needs to go through a whole cycle (of course even this assumes that the harested seed will supposedly used as its farther – be best primed for the future similar seasonality; thta is all)
- so my bet is – it totally depends on what kind of environement and cycle you want to grow, you do not have to follow that particular recommendation if your intended growth cycle is different from the typical farming situation.
now let’s assume your intention is to grow as all other typical farmers, then the following is a guide –
Plant lettuce in the spring before hot weather arrives. You can also plant lettuce in the late summer for a later fall harvest. To collect the seeds, wait until the flower stalks grow and mature, usually about two to three months after planting. (this of course will depend on a few other factors, but mostly how much sunshine it has received – the more the quicker flowering, this is a generally accepted theory, you should try and find out yourself for your own particular growing media and environment) Flowers form in groups of 10 to 25 and will each form just one seed.
Harvest lettuce leaves when they are large enough to consume. Leave the flower stalk behind and wait three weeks after the flowers have appeared in order for the seeds to mature and dry.
Place a clear plastic bag loosely on top of the flowers if birds are eating the seeds. The seeds can continue to form and dry during this time.
Harvest the seeds by cutting off the stalks and bringing them indoors. Then hang the stalks upside down for a day indoors and out of the sun to dry.
Shake the flowers for the seeds to drop. If they don’t drop, rub the flowers with your hands until the seeds separate from the flowers.
Store lettuce seeds in a sealed container and place it in the refrigerator to plant in the spring or summer.
here are some ttricks and lessons –
A trick I like for starting seeds in the summer is to thoroughly soak the area to be planted about 2-3 days before sowing. Cover the damp soil with a wide board and lift it and repeat this process daily, if the weather is particularly hot and dry. Within a couple of days, the soil under the board will be cooler than the surrounding soil. Sow your seeds, water, and cover again with the board. Check daily for signs of germination. At the first sight of
http://gardening.about.com/od/problemspests/f/Why-Does-Lettuce-Bolt-And-What-Can-I-Do-About-It.htmeen sprouts, remove the board.
here is something you should know about lettuce –
Lettuce grows best in full sun in loose, nitrogen-rich soils with a pH of between 6.0 and 6.8. Heat generally prompts lettuce to bolt, with most varieties growing poorly above 75 °F (24 °C); cool temperatures prompt better performance, with 60 to 65 °F (16 to 18 °C) being preferred and as low as 45 °F (7 °C) being tolerated. Plants in hot areas that are provided partial shade during the hottest part of the day will bolt more slowly. Temperatures above 80 °F (27 °C) will generally result in poor or non-existent germination of lettuce seeds. After harvest, lettuce lasts the longest when kept at 32 °F (0 °C) and 96 percent humidity. Lettuce quickly degrades when stored with fruit such as apples, pears and bananas that release the ripening agent ethylene gas. The high water content of lettuce (94.9 percent) creates problems when attempting to preserve the plant – it cannot be successfully frozen, canned or dried and must be eaten fresh.
comment – so it seems that the best way to grow lettuce should be –
- full light
- keep temperature of 18C
- pH – 6.0-6.8, very slightly acidic
two most important factors you should consider – light and temperature
lettuce can be grown in many systems. the following are a few to start with –
- By growing lettuce in an aquaponic system it can be grown year round with the addition of extra lighting indoors. To offset the cost of the lighting being able to grow lettuce year round means increased aquaponic lettuce production and higher yields. Though many different leafy greens will grow successfully in an aquaponic environment there are a variety of lettuces that do especially well. These include Bibb, Red Leaf, Oak Leaf, Pinto, Columbus, and Iceberg. Head lettuce is not usually a profitable crop because it requires a high level of nitrogen and a lot of water so by using an aquaponics system the farmer is able to provide both in abundance. The Bibb variety of lettuce is often suggested as a good beginner crop for the budding aquaponic farmer.
- The suggested method for growing lettuce aquaponically is to create a bed for the seedlings and suspend them in a polystyrene or other foam material floating over water that has been pumped from the fish tanks. The roots need to sit in the water but not be submerged. This can also be achieved by sitting the seedlings into a thick layer of gravel and allowing the water to flow across under the roots. It is important that the lettuce not sit in water because it will cause the roots to rot and the crop to fail.
Scientists have been looking at the flowering phenomenon known as bolting to learn how we might better our odds of keeping a palatable crop.
Bolting can be seen in a variety of crops, including beets, cabbage, celery, radicchio, and lettuce, but especially in lettuce. And lettuce is the crop in which bolting has been studied most extensively. Lettuce’s penchant to bolt and turn bitter is well known. What’s less well known is why it happens.
Many say that early bolting in lettuce is accelerated by high temperatures, but experiments have shown that temperature alone is not the deciding factor. What then controls when a lettuce plant will bolt? And what causes the bitter taste connected with seed stalk formation?
here is what we know till now, we can learn and deduce what is and what is not –
Cumulative light exposure causes bolting
The discovery that lettuce’s transition from vegetative growth to bolting is influenced by cumulative periods of light was first made in Germany in 1931. Some plants in the field were simply covered so they had different daily exposures to light, and only plants given long daily periods of light bolted normally.
comment – this makes sense from the physics perspective. everything accumulates and eventually exerts its effect. light as the main source of energy should dollow the same rule.
higher temperature – bolt or not????
In 1995, William Waycott, at the United States Department of Agriculture in Salinas, California, described a number of experiments that dealt with the interaction of temperature and day length on bolting. Plants grown in plant growth chambers under short days of eight hours of sunlight at a steady high daytime temperature of 90˚F grew to harvest maturity without bolting.
Waycott also examined the bolting response in greenhouse experiments, which were started in January, when the days are short, and in July, when the days are long and temperatures sometimes reached 95°F.
Plants grown on short days bolted about 135 days after planting, compared with about 90 days for plants on long days, and neither short-day nor long-day plants had premature bolting. Thus, total day length and not temperature determined the time of bolting. This can be explained by the existence of a genetically controlled clocklike mechanism that tallies the number of light hours required for a given cultivar to bolt.
it seems that – total light exposure is the main factor in determine the bloting.
What causes bitterness in lettuce?
Scientists are sure that lettuce turns bitter after bolting. Biochemists have identified compounds responsible for the bitter taste of lettuce. These substances are in a class known as sesquiterpene lactones. These molecules have 15 carbon atoms or more arranged in rings.
The plant builds the rings in a number of steps starting with acetic acid (vinegar), which has two carbon atoms. Leaf bitterness has been highly correlated with the levels of one compound in particular, lactucin glycoside, in which the sesquiterpene is combined with a sugar molecule.
Before lettuce bolts, the bitter compounds are present at very low levels. But they increase in the leaves during flowering. Some wild lettuce species have higher concentrations of sesquiterpene lactones than domesticated lettuce. The wild lettuce has been used in breeding because it can introduce virus resistance, but breeders have had to be watchful not to introduce the bitter compounds along with the resistance.
The bitter compounds are also found in the milky juice, or latex, located mainly in the stems of lettuce. Laboratory experiments revealed that these compounds provide insect resistance. They have been shown to retard feeding by locusts, and may also act to repel burrowing insects.
here is some great comments i found by a very experienced gerderner about bolting –
A wide range of genetic expression for bolting is possible. For instance, there is a dwarf mutant of lettuce that shows extreme resistance to premature bolting and may become useful for breeding purposes. At the other end of the scale, there are mutants of crisphead-type lettuce that flower unusually early. In an experiment, a normal lettuce flowered after 150 days in a greenhouse, whereas a mutant flowered in 55 days. In its haste to produce flowers, the mutant went from seedling to flower without first forming rosette leaves or heading (this is what one should be alert about in breeding). i think what we know about viagra is relevant here – let it grow fast, but block its bloting, that is the key.
here is his website you can find more details that we can learn –
Lettuce (Lactuca sativa) is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. It is eaten either raw, notably in salads, sandwiches, hamburgers, tacos, and many other dishes, or cooked, as in Chinese cuisine in which the stem becomes just as important as the leaf. Both the English name and the Latin name of the genus are ultimately derived from lac, the Latin word for “milk”, referring to the plant’s milky juice. Mild in flavour, it has been described over the centuries as a cooling counterbalance to other ingredients in a salad.
Lettuce plants should be grown in a light, sandy, fertile, humus-rich soil that will hold moisture in summer. A soil pH of 6.5 is preferred (this slight acidity in fact goes against the common ph nature of the aquaponic system, but it is interesting to note that lettuce has been grown aquaponically throughout the years. so the acidity itself sometimes is not that critical.); lime may be added for this purpose. For best eating quality, water is essential; the plants prefer the soil to be moist at all times.
- ph = 6.5
Lettuce plants prefer cool weather, ideally with day temperatures below 75 degrees Fahrenheit (this is asbout 25 C, ok for fish of most kinds) and night temperatures above 40 degrees Fahrenheit. Hot, sunny, or dry conditions may cause the plants to turn bitter and produce a flower shoot, a process known as bolting. Therefore, lettuce is often grown in the coolness of spring and autumn in the Northern Hemisphere; lettuce sown in summer is often grown in light shade. In addition, bolt-resistant summer cultivars of lettuce may be recommended as temperatures increase.
- temp = 25C
Lettuce can be direct sown in the garden, but lettuce plants are often started in cold frames or greenhouses, and the resulting seedlings transplanted to the garden or field. This allows an earlier start, or allows more efficient use of garden space, (but of course this assume labor cost is less than the space cost as the case in China) as the lettuce can be transplanted when growing rapidly, avoiding the use of garden space for germination of seeds.
- seedling is slow, so only grow more mature lettuce in the commercially precious field. in fact this shuld be the best practice for most plants, it is common that germination takes time and farming space should be saved only for the last stage of the growing.
As another way to allow an earlier crop in cold weather, lettuce is sometimes given glass protection, known as a cloche, or protected with spun material known as a floating row cover. In sufficiently mild-weather climates, these same protective devices (greenhouses, cold frames, cloches, row cover) may be used to protect lettuce throughout the winter, allowing harvest even in near-freezing or freezing weather. Lettuce is hardy to Zone 6.
Lettuce is often grown between rows of slower growing plants like brussel sprouts or broccoli. This is called a catch crop. It allows more efficient use of garden space, and also provides the lettuce with needed shade in warm weather.
try to avoid this – lettuce bolting –