You are growing cukes indoors? What kind of set up do you have, if I may ask?

Anyway, you really don't want to side dress with anything. Granular fertilizers work best outside. For container plants you are better off with liquid fertilizers that don't require any biological processing or weathering before they release the nutrients.

As a rule you would look at the coloration of the leaves to determine if the plant is getting enough nutrients. How light/dark green the leaves are will vary by variety, but there should be no yellowing or burning at the edges or the leaf veins being chlorotic.

Cucumbers use NPK similar to most plants which is to say in a 3:1:2 ratio so a fertilizer with 9-3-6 or 12-4-8 would be fine. You are going to want a fertilizer that supplies all nutrients, not just NPK for best results unless you have another means of supplying the secondary nutrients. Dyna Gro makes a good product that fits the bill called Foliage Pro.

If you would like to see the ratio of both major and minor nuttrients various vegetables use then see this link.

>>3:1:2 ratio so a fertilizer with 9-3-6 or 12-4-8 would be fine.

Oh I thought the middle number had to be high for flowering.

I'm using Miracle Grow (15-30-15) every 10 days and then Dr. Earth Organic 5 (5-7-4) side-dress the soil once a month. You're saying that the yellow tips is lack of nutrients??? Not too much??? That must mean that the microbes in the Dr. Earth are not doing their job.

The middle number being high (phosphorus) is a complete myth. Unfortunately it seems most of the horticultural retailers are all too willing to continue propagating this myth even as some cities are banning the use of fertilizers with *any* amount of phosphorus due to pollution of soils and water ways. You may notice that many products these days such as detergents are being advertised as phosphate free. They are an environmental problem when present in excess.

I don't know of any plant that requires more P than N or K and most plants require more calcium than P.

I am not saying you can't use up what you have on hand, just that it isn't the ideal.

I can't diagnose what yellow tips on the leaves means. There are many things it could be and it may not be at all serious in terms of how your plants will yield. I am more curious as to what kind of set up you have indoors to grow cukes.

An awful lot hangs on how you are providing enough light to these plants. If you have HID lighting then maybe it will work, or if you have a sun room that gets full sun all day long it might work, but otherwise it's going to be lack of light that will be the limiting factor for flowering and fruit development.

The first setup is a 3.5 gal container with 3 rapid growth (but stunted) cucumber plants that have been blooming since the end of December. The fixture has 2 GE Plant and Aquarium 40w 48" long bulbs. All growth looks hardy on the 6" ring trellis, but each plant has at least 50 male flowers blooming madly. Occasionally a female shows up but she bails before producing a healthy fertilizable blossom. A double layer of mylar drapes over the light fixture and down to the floor. I secure the sheeting so very little light escapes. A triple sheet of mylar lays across the soil. When you look under the hood, the setup is very bright.

The 2nd setup is actually for lettuce, spinach, and a rogue cucumber. This late sprouter didn't have a home, so he lives with the lettuce in a non-trellised large rectangular box 35"long X 18"wide X 6"deep. The fixture has 2 Phillips Plant and Aquarium 40W x 48" bulbs and loosely covered with a triple thickness of mylar. So far, the plant looks, grows, blooms, and produces like a traditional cuke. HeÂs slowly taking over the container. Because the bulb is supposed to only be for greens and not flowering stuff, I didn't expect anything from this late bloomer. However, it has three 2" cucumbers and a couple more females on the branches but some yellow and a few burnt tip leaves.

Both plants are getting the same amount of fertilizer. Maybe the container is too small or the light is too intense for the non-bearing (but wildly blooming) container. Once the plant is growing well, how many inches are your cukes from the light source?

I'm going to cut down the 2 of the 3 non-producing cuke plants from the first setup and maybe re-plant the container. Justaguy what is your cucumber setup? Do your cukes bear indoors?

I do not grow cukes indoors. I have an HID lighting setup I use for starting plants and for overwintering some, but I gave up long ago on trying to grow high light veggies to harvest under lights. I am certainly not going to say it can't be done, just that I didn't consider it cost effective. It is fun and rewarding in it's own way, but not cost effective. A 400 watt Metal Halide light will properly illuminate about a 3x3 area, and perhaps a 5x5 area with reflective sides around the growing area. I would be growing $50 cukes :) I took my passion for growing under lights into the aquarium hobby and have fresh water planted as well as a salt water reef tank. Those are enough work and are both very efficient at growing lots and lots of algae :)

In your case you are using fluorescent lights and these do not have anywhere near the intensity of light that HID lighting does. With HID lighting you can have the lights 3 or more feet above the plants, with floros you want it no more than 6" away from the plants. This effectively reduces the coverage area.

At this point I am going to say I think lack of light is your limiting factor and fertilizer isn't a concern. One other thought is what type of cukes are you growing? For indoor you are going to want the so-called greenhouse varieties. You need plants that are gynoecious (all female blooms) and parthenocarpic (do not require pollination). Diva is a variety with both traits.

I am going to refer you to the Growing Under Lights forum here at GW. It doesn't seem to get a lot of traffic and I haven't participated there in years, but it is probably frequented by more folks than this forum who can help you understand what is going on with your cukes and what it will take to get a set up that will allow you to grow darn near anything indoors.

Another question.

The fertilizers seem to be geared toward vegetative growth and flowering. Haven't seen anything toward actually growing/producing the fruit. Which fertilizers do that the best esp for cukes?

>>At this point I am going to say I think lack of light is your limiting factor and fertilizer isn't a concern. One other thought is what type of cukes are you growing? For indoor you are going to want the so-called greenhouse varieties. You need plants that are gynoecious (all female blooms) and parthenocarpic (do not require pollination). Diva is a variety with both traits.

Thank you so much for your help. I'll look into the better lighting AND different seed. SpaceMaster 80 seems to only be doing marginally.

Another question.

The fertilizers seem to be geared toward vegetative growth and flowering. Haven't seen anything toward actually growing/producing the fruit. Which fertilizers do that the best esp for cukes?

A fert in a 3:1:2 ratio :)

The ratio of nutrients a plant requires for optimal growth and development doesn't change a whole lot. It might change from a 3:1:2 ratio to a 3:1:3 ratio, but that is about it. A plant's nutritional needs are remarkably the same regardless of life stage. Getting it wrong by a little bit isn't likely to produce a result difference you or I can measure. Just getting close is more than most will ever do.