I am in Minnesota and we are experiencing the same weather. Cukes like to be very warm, and will just sit until it warms up. I am waiting to plant them and melons until it does and they grow a little more in my hothouse. The squash plants are going in today since they have gotten so big, I cant wait anymore. I would not fertilize at all right now. You risk burning the plants since they are not actively growing. Just wait. My beans are also sickly yellow. I don’t usually plant until June 1st(beans, corn), but I gave it shot and have learned once again that here in MN(just north of St Paul) it is a waste of time. That’s why I start many things in pots on May 1st. As for the flower on the tomato, remove it. You don’t want that tiny plant setting fruit, it needs to put its energy into growing foliage. Good Luck! Hopefully, warm weather is finally here!!

hold that fertilizer while plants are stressed or unknown condition, water in the morning and keep check with status. If frost damage, we know there’s no solution. at this point tomato is concerned the most.

Tomato plants should not even be planted untill the minimum temperature at nights are no less than 50 degrees..peppers and cukes shouldnt be planted untill outside temperatures are around 65 to 80 degrees outside..this will stunt the fruiting process and photosynthesis of the plant giving a poor harvest if any at all….I grow a garden 12 months out of the year and start my seeds under lights ..even when the chance of last frost have vanished..I do not plant my plants outside untill the temperatures above I listed are met….Heres some pictures..I do know veggie gardening very well..

Concerning tomatoes and temperature
http://groups.ucanr.org/mgnapa/Articles/Best_Time_to_Plant_Tomatoes.htm

Concerning peppers..

The Growing Season

If compost and manure are added to the vegetable bed each year, then additional fertilizing shouldn’t be necessary for the pepper plants. However, the seedlings can be fertilized with fairly high levels of nitrogen to encourage vegetative growth in the beginning. Once the plants are established, however, more fertilizer should not be applied unless the plant shows nitrogen deficiency such as yellowing leaves or stunted growth.

In fact, once the plant begins to flower, excessive nitrogen will cause the blossoms and small pods to drop off since the plant will put its energy back into vegetative growth instead of fruit production. For maximum fruit to set, night temperatures should be between 65 and 80 degrees F. Fruit won’t set at all if night temperatures rise above 86 degrees F or daytime temperatures rise above 95 degrees F because excessive transpiration results in blossom drop.

The soil around the pepper plant should remain moist but not wet. Flood irrigation using a garden hose in furrows between the rows can be used. However, soaker hoses or drip irrigation lines are more efficient and don’t waste as much water. Overhead watering should be avoided because it encourages fungal diseases and the leaf canopy will block the water and result in uneven watering.

Copied from the link below..please take note on the fertilizing with nitrogenn..pepper plants detest it ..all the nitrogen they need is from a good organic compost..they need phospherous and potasium when they start to bloom to set fruits..if you use high nitrogen yopu will get legggy plants with no fruits are the blooms will drop off on you..Eggplant and cucmbers are about the same as well..none of these produce very well when planted too early..check out my garden pictures below..

http://www.mastergardeners.org/projects/pepper99.html