I am growing Romaine in pots and everyday I have a new pale leaf on the heads, not rotten though, just light colored and about 4 inches high. It is grown on my deck in NY.
This is something called blanching. It happens when the plant does not get enough light. Some people like to do it on purpose to more bitter flavored lettuces and greens to sweeten their flavor. It can be corrected by giving the plant some more light.
I have recently let my red leaf lettuce grow too much, and now the leaves are hard and there is milky white liquid that is coming from the stalk when I cut it. What is this, and is it still ok to eat the lettuce after it's gone to seed?
It is safe to eat but when lettuce goes to seed, it develops a bitter flavor and does not taste good. The milky substance is just the juice, or sap, of the mature plant.
I can't grow lettuce that isn't bitter. What causes this? Also, how can I prolong or even prevent broccoli heads from flowering before they are large enough to harvest?
Some lettuce is naturally bitter, but heat or a lack of water can also make lettuce bitter.
This article will help you with the broccoli bolting:
https://www.gardeningknowhow.com/edible/vegetables/broccoli/bolting-broccoli-growing-broccoli-in-hot-weather.htm
Why does lettuce taste bitter? Is something needed in the soil? Some of the cucumbers also taste bitter. Is the fault in the soil?
This will explain about the lettuce:
https://www.gardeningknowhow.com/edible/vegetables/lettuce/bitter-lettuce.htm
And this about the cucumbers:
https://www.gardeningknowhow.com/edible/vegetables/cucumber/what-causes-bitter-cucumber.htm
I am new to gardening in a greenhouse and I would like to start lettuce and tomatoes in a soilless medium but I really don't understand what a soilless medium is or how to go about making the soilless medium.
This article should also help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soilless-growing-mediums.htm
Soiless medium is just that, there is no regular soil used in the mix. There are advantages to using this mix when you are starting seed, you have better control of what's in the mix, with less chance of contaminates or diseases and fungi that could be present in regular garden soil.
You can either buy the mix or make your own. The following site has some excellent suggestions for recipes for making your own. I have used several of them with great success.
http://gardening.about.com/od/seedsavin1/a/Potting_Mix_2.htm
In my garden I have red lettuce and romaine lettuce. The heat has caused them to grow very high and now sprouting flowers. I know from the past they are not quite ready for a full harvest. Been picking the leaves as needed; however, never seen them to sprout like this. Please help me with this, as I don't want to lose the crop. Does the constant heat make veggies react differently? Should I harvest early? Even my green and yellow peppers are growing before it's natural harvesting time. Thank You
It sounds like your lettuce is bolting; lettuce is a cool season crop. the peppers should be fine, just harvest them when they're ready, it has been a hot summer, more about the lettuce here:
https://www.gardeningknowhow.com/edible/vegetables/lettuce/bitter-lettuce.htm
and about bolting here:
https://www.gardeningknowhow.com/edible/vegetables/vgen/what-is-bolting-what-it-means-when-a-plant-bolts.htm
My leaf lettuce oozes a milky substance when I pick it. Is this normal?
Yes, it is normal for some leaf lettuce, here is more leaf lettuce information:
https://www.gardeningknowhow.com/edible/vegetables/lettuce/harvesting-leaf-lettuce.htm