If yellowing, they've been on the vine too long.

Cucumber plants have shallow roots and require ample soil moisture at all stages of growth. When fruit begins setting and maturing, adequate moisture becomes especially critical.

For best yields, incorporate compost or well-rotted manure before planting. Cucumbers respond to mulching with soil-warming plastic in early spring or organic materials in summer. Use of black plastic mulch warms the soil in the early season and can give significantly earlier yields.

Side-dress with nitrogen fertilizer when the plants begin to vine.

In small gardens, the vines may be trained on a trellis or fence. When the long, burpless varieties are supported, the cucumbers hang free and develop straight fruits. Wire cages also can be used for supporting the plants.

Do not handle, harvest or work with the plants when they are wet. Good luck with your cucumbers this year. Water! Water! Water! They need lots of water.

Definitely run them up a trellis. Every few days just weave the new growth around the trellis and it will naturally grow up it.

And don't plant too many in one spot. The seed package says to plant 3-5 seeds per location, but I only do two seeds per hole, with about 10" spacing. I've never had one seed not germinate on me, and I think they get overcrowded if you plant too much. I germinate my seeds in on a paper towel inside a plastic bag on top of my water heater for 2 days before putting them in the ground outside too.

Sounds like you are doing well at growing cucumbers. The burpless types are Asian cucumbers and they do not look like standard slicing cucumbers. Many of them are much lighter in color than than the dark green slicers. A trellis does make for more perfect cukes, particulary with burpless which tend tend to be long and skinny and will will curve on the ground.
Jolly green a burpless type {{gwi:25536}}
Thunder, a standard slicer {{gwi:35044}}

You don't mention feeding them at all. I assume you are regularly feeding and watering the plants? Heavily mulching them with straw or hay or grass clippings will also help stabilize the soil moisture levels they require.

I agree that burpless varieties don't look like store bought cukes. If you want the appearance of store-bought then I suggest you try one of the common slicing varieties like Marketmore.

Dave

Honestly, I find "burpless" cukes lacking in flavor compared to old-fashioned slicers and, my favorites, picklers.

When stressed the regular cukes can indeed become bitter, but if you keep them evenly watered and pick them before they get too old the flavor is incomparable.

How do you know exactly when to pick them? Do you check for yellowing or if they get soft to the touch? Should they just 'fall' off the vine?

I would think cucumbers are pretty much good to eat even if they are quite small. The more you pick them; the more they bloom and make more cucumbers. As long as you have bees and keep them watered and fertilized and picked you should have tons of them. Just pray for no cucumber beetles.

Oh and don't overhead water if possible. Run a soaker hose or drip system and let they get water long and slow. Dry leaves discourage things like powdery mildew.

If they are soft or yellowed I throw them right into the compost pile because they are overmatured. Good cukes are nicely green (sometimes darker, sometimes paler depending on variety), firm, and crisp.

Different breeds of cukes naturally grow to different sizes, but all are OK to pick as young as you want to. You can experiment with letting them grow to different sizes to see what you like best (personally I prefer the flavor you get when the seeds are present but not overly large and, especially, not yet developing their hard shells).

If you think of the different sizes you find in pickle jars, those are good sizes to pick pickling cuke varieties while the grocery-store, slicer types are usually good when picked at the size you'd find in the grocery store.

Don't be afraid to experiment about when you pick the variety you've chosen -- pick some very small, let others grow somewhat larger, and let others grow to the full size that the seed envelope says they get too. That way you can decide how you like them best.

In addition to size, the flavor will also differ depending on how much rain you've had and how warm or cool the weather is. Stressed cukes, either suffering from heat or drought, often become bitter. Mulch helps moderate this problem.

Good luck getting the cukes you like most this year. (btw -- my kids love to eat cucumers fresh out of the garden. I just wash them and rub the spines off).

I read many good advice, as how to care for cukes.
About size and picking ; cucumbers picked the younger, the smaller the tastier. I don't care about giant cukes. Here is my test: slice it lengthwise. Slightest hardening of the seed pockets means that they are overgrowned. Tender cukes should have unformed tiny seeds with no chewy hardened seeds.
Another thing is that when cukes are left on vine, the vine will almost stop producing. Because it spent all of ots energy to care for the seeds.. that is what its mission is, to produce seeds, not slicers for our table.

Do not handle, harvest or work with the plants when they are wet.

I pick in the morning before the dew dries. Never picked a bitter cucumber.

Hi, a few years ago I was stuck in a problem like you, In first place I tough that my seeds was wrong but after a few test I can saw that my seeds was not the problem because the seeds were well so, a friend of mine recommended that the cucumbers plants need some type of support to keep them off damp ground, where diseases have a heyday. I highly recommend you take a look to this article and tell me what did you think. I tell you this because you use a vine variety and any that are vining type can climb the trellis. Actually I'm using a type of Hortomallas and I have very good results.

http://www.hortomallas.com/en/grow-squash-cucumbers-and-melons-vertically/