The vegetables discussed here all pose a different challenge to gardeners. Some never seem to fill out and others grow but don't taste good. I hope you won't have problems with all of these vegetables, but if you are struggling to grow them, here are some tips to get a better harvest.
Carrot seeds are tiny, making it difficult to plant them evenly. Plant them only about 1/4 inch deep. Spacing the seed about an inch apart is ideal, but impractical. Chances are good you will wind up doing some thinning. Thin any plants that are within a 1/2 inch of each other, when the seedlings reach 1--2 inches tall. Snipping or pinching the seedlings off at the soil line is the best way to avoid hurting the remaining roots.
If you need to thin again later, you can use the tiny carrots in salads. When you've finished thinning, your carrots should be far enough apart so they won't rub shoulders when mature.
Carrots can be easy to grow or they can give you endless grief. Here are some common carrot growing problems and how to avert them. The Seed Never Germinates: Carrots won't break through encrusted soil. Make sure you keep the soil moist, but not soaking wet. Don't let it dry out and crust over. An old trick for keeping the soil loose is to plant radish seeds right up next to the row of carrots. The radishes will germinate first and keep the soil loose. Another trick is to cover the seed with sand or vermiculite. These won't make as hard a coating as garden soil.
Plants Go Right to Flower and Seed and Never Develop Roots. Don't put your seed out too early. Carrots are biennials and low temperatures make them think they've already gone through winter and it's time to go to seed.
The Shoulders of the Carrots are Green and Bitter. This is an easy one to fix. Just make sure the whole root is covered with soil. Exposure to sunlight will cause them to turn green from developing chlorophyll.
Skinny Carrots. This usually is caused by nearby weeds that compete for nutrients and water. Keep the area weed free.
Short, Stumpy Roots. The soil is probably too warm. If the soil heats to over 70°F, the roots become stunted. Use a mulch and keep the soil well watered during hot spells, to keep the soil cool.
Deformed roots. Forked or bent carrots are the result of something getting in the way of the developing root. Either the soil is too hard for them to grow through, or they hit a rock, or maybe there's another carrot planted too closely. Make sure the soil is tilled and soft at least a foot down, before you plant. And thin your carrots early.
If you've done all that and you still get forked roots, the problem could be root-knot nematodes. If that's the case, you will need to solarize the soil by covering it with clear plastic and letting it fry in the summer sun. Definitely remove the carrots before you cover it.
Roots Crack Done the Side. Cracking is caused by inconsistent watering. Carrots that are left dry for a period and then given a lot of water will swell up and crack. Give them water every week and mulch the area so the soil remains moist. Also harvest when the roots are mature. Leaving them too long is another cause of cracking.
Carrots have Lots of Tiny Roots All Over Them. This is caused by too much nitrogen. Don't over feed your carrots and don't you a high nitrogen fertilizer.
Bitter Carrots. Carrots like cool soil. If the temperature never cools off at night to at least somewhere near 60°F, they will use up some of their stored sugars to acclimate. Keep the soil moist and mulched and maybe hold off planting carrots in the middle of summer. Hope this will help with growing carrots. More coming on vegetables that are hard to grow.
taken from http://gardening.about.com/od/problemspests/ss/Five-Challenging-Vegetables-to-Grow
Till next time, this is Becky Litterer, Becky's Greenhouse, Dougherty, Iowa