Do you remember when you planted it? To give your broccoli time to mature and form heads, it is best to plant about 10-12 weeks before the first killing frost. Usually, broccoli planted later than that tends to freeze and may fail to produce heads. It depends on whether the growing tips were severely damaged when they froze. Of course, it also depends on the variety you planted. There are some types of broccoli that will overwinter, but you generally have to specifically choose an overwintering variety (and they are not easy to find)--the standard spring-type varieties aren't as cold-hardy.

Broccoli produces best when the air temperatures are in the 45-70 degree range. Once the air temps drop into the low 40s and stay there pretty consistently, the plants will be stunted. Later on, if the temps warm up, small heads may or may not form, but you're unlikely to have as good of a harvest as you would have if the temps had stayed warmer.

I'm guessing it is the cold night time (and sometimes cold day time as well) temperatures that are causing your problems with your broccoli, but there could be a couple of other issues as well.

Here's a couple of things that can impact your broccoli harvest:

1. Soil that is too acidic. (This is common in many parts of Oklahoma.) Broccoli does best on soil that has a pH between 6.0 and 7.5. If your soil is too acidic, you can add lots of organic material plus agricultural lime to try to raise the pH to the right level.

2. Soil that is too sandy. Broccoli actually grows better on heavier soil, as long as the heavier soil has adequate drainage. If your soil is very sandy and is low in organic content, broccoli will struggle. The best broccoli I've ever grown was in a raised bed with clay soil heavily amended with compost and cow manure.

3. Soil that lacks fertility. Broccoli has a fairly small and shallow root system so it needs lots of organic material (compost, manure, etc.) in the upper levels of the soil to keep it growing happily. With broccoli, you want somewhat luxuriant growth prior to the formation of the heads. In general, the larger the plant, the larger the head and also you'll have a lot more sideshoots. Broccoli is a heavy feeder, so I like to feed it with a good organic fertilizer every couple of weeks. I normally use compost tea, Garrett Juice or manure tea. If you use commercial, chemical fertilizers, broccoli benefits from a fertilizer with a 1-2-1 ratio although fall crops can get by with a high nitrogen fertilizer (like ammonium nitrate or sulfate) if the broccoli is in a bed that was fertilized in the spring.

4. Growing conditions that are too dry. Broccoli likes water and lots of it, as long as the plants are in well-draining soil or in raised beds to facilitate good drainage in slower-draining soils. Because broccoli has relatively shallow roots, it must be watered more frequently than plants, like tomatoes, that have more extensive root systems.

I hope you won't give up on growing a fall broccoli crop. The big advantage to growing broccoli in the fall is that you will have significantly less trouble with cabbage loopers and cabbage worms than you'll have in the spring. (Bt, an organic caterpillar killer, is the solution, but you have to apply it carefully so it won't kill the desirable butterlies and moths.)

Seed of overwintering broccoli that you plant in the fall and overwinter for a late, late winter or very early spring harvest is hard to find, but I have found some of the overwintering varieties at Territorial Seed (in their fall/winter catalog--not in their spring catalog) and at Seeds of Change in the past. Some of the overwintering types include Rudolph, Rubine, Purple Sprouting and White Sprouting. Four or five years ago, I bought a winter broccoli blend from Territorial Seed that had several winter varieties in one package. You also sometimes can find overwintering varieties from British seed companies.

If you are in zone 7B, some of the commonly-grown fall varities like DeCicco, Umpqua, Nutribud, Early Green and Calabreese may overwinter for you in a milder winter.

Dawn

AS usual, Dawn has answered very thoroughly. But I will add something out of my experience. I used to try to plant broccoli both spring and fall, but had such inconsistant results in the fall, that I gave it up in favor of spring planting only. I very much doubt that you will get a crop, broccoli that is stunted for any reason, cold weather, hot weather, dry soil, root crowding in the pot before transplanting, almost always "buttonheads"--makes tiny bitter heads instead of large sweet ones. (This is why transplants you buy in the spring almost never make good heads. CAbbage can have its growth interrupted and when planted go on to produce well, but broccoli doesn't.)I start my seed the first of Mar on a heated plant bench on a glassed porch, keep them growing well and plant them about the same time as I do tomatoes between Apri 1 and 15. I plant 3 rows of 30 plants each, 18" apart. For years I planted only Early Emerald from Park's seed and got plants that made sweet juicy dinner plate size heads, most of which I freeze. I don't usually try for side shoots as by the time the plants start making side shoots, they are too strong for our taste, despite being mulched and watered. I pull all the plants by midJune and throw them to the chickens. Park's quit offering Early Emerald in favor of Early Dividend, a good tasting broccoli, but a little smaller plant and head than Early Emerald. After the first year, I planted them a little closer together.

If you are the experimenting type, you could leave your plants in the ground just to see what will happen.

Thanks both for the info. Don't remeber what variety they were i think two different types i have the packets just have to dig to find them. Dawn i think i planted maybe six weeks before our first (early) killing frost.
Sounds like i'll pull them been out scratching my head organizing for spring and they are right where i want my pepper plants. Priority goes to peppers for me i believe. I'll try like you suggested mulberry on my planting times for spring. One of the compost piles will love the green plants anyway. Or maybe the new worms i got for christmas from DW.

New worms for Christmas! That tells me that your DW completely understands your interest in gardening. : )

Success with broccoli in our climate is often a matter of weather, too, which cannot be controlled.

Like Dorothy, I don't have much trouble getting a good spring crop, in general. But, and this is a big 'but', if we have atypical weather, it can cause all kinds of problems with the broccoli. Here are a couple of examples of how erratic spring weather can hurt the broccoli crop:

1) If we have the kind of spring here in extreme south-central OK where we are hitting the 90s every so often in March-April, the broccoli doesn't do as well. Too much heat too early makes it want to form heads too soon and can cause the heads to flower before they reach a decent size. And, as Dorothy noted above, too much heat creates a very strong and unpleasant flavor.

2) If we have a long, cool, "mild" spring, like we did in 2002, where the nights stayed in the 40s into May, the broccoli does great, assuming we don't have a prolonged cold spell of about 2 weeks with overnight lows consistently below 45 after the broccoli is in the ground.

3) If we have a fairly typical spring with some warmth and some cold, but we have a prolonged late cold spell, esp. if it is accompanied by ice or snow, the broccoli crop may stunt and not form heads. This happened at our place in 2007 (or maybe it was 2006?).

4) If we have extreme drought (as defined by the NWS) carried over into the late winter/early spring from the previous year and rain is not falling, my spring broccoli crop will fail unless I irrigate heavily to make up for the lack of rainfall.

Fall broccoli tends to be a little less of "a sure thing" because the summer heat/dryness can hang on too long and really stunt it. If it is a somewhat rainy autumn, though, I usually get a great fall crop and it is so wonderful not to have to fight the cabbage loopers and cabbage worms, which I never see here in the fall.

I can get a whole lot of broccoli per square foot if I plant one plant per square foot in very heavily enriched soil that is well-irrigated. My favorite broccoli for intensively planted beds is Small Miracle.

Dawn