A very newb question about seasons/"putting garden to bed"

I feel embarrassed just asking this because it seems so general, but I feel like I hear conflicting things.
Do all the plants in a garden have to be pulled out at the end of their growing season? I have heard this, but it surely cannot be true, right? If I pulled out my iris bulbs, they won't be able to multiply, and it's the same with everything else. It won't come back the next year if I pull it out! I must be missing something, because I don't intend to pull anything (and I'm in Arizona, so 1. it's hard enough to get them to grow at all, and 2. many plants are growing all year anyway) but I don't want to mess things up by not pulling what I should. Here's what my baby garden has in it so far:
1 Tangelo tree (about 1.5 yrs old)
a couple of tomato plants
1 red onion (grocery store variety that started to bloom so it got planted)
1 agapanthus (less than a year old, still pretty small and growing slowly.. not enough direct sun IMO)
1 very tiny red yucca
an area of Dutch Iris that had a few blooms this spring (just planted them in October or November)
3 tufts of bamboo muhly grass (one is in a container)

The tree was planted a little over a year ago as a sapling, and everything else has been planted within the last year.

Wow, I envy you your zone.

You would only need to dig up and store bulbs, corms or plants that wouldn't winter over in your garden. In other words, if it gets too cold, and they would freeze, which would not be a problem in your area.

For example, some people can't leave the iris in the ground because the ground freezes. It doesn't freeze here so I don't need to dig them up. I have a white agapanthus that I left in the ground this winter, and it is fine, too. Your little tangelo tree would be fine outside all year in your area, but I would have to mulch it heavily and cover with frost cloth when a freeze or frost is predicted. Others in colder areas than I am in would have to keep it in a pot so they could take it inside for the winter.

There are several people here who live in Phoenix, Mesa or Tucson who can advise and help you with growing plants in your area. From what I see of their posts, a problem for your garden may be your very high summer heat instead. They can help you with how to manage that.

Karen

I have LOT'S of flowers (including bulbs), shrubs and trees galore on my 5 1/2 acres that I never dig up. They have wintered over with no problems. You shouldn't have any problems where you are. I'd just leave them in the ground. As glendalekid said, watch your weather. If you should happen to get a freeze warning, then you would have to do something to protect your tree but your ground won't freeze deep enough to harm your bulbs or other flowers.

In case of a freeze/frost warning, a couple of warm blankets thrown over the tree will work fine. Just be sure that the blankets go all the way to the ground all around the plant. When my son was attending UTI in Phoenix the winter of 85-86, Phoenix actually got an inch or so of snow one day. So, while it's very rare, it can happen.

Karen

Thank you. My irises and tangelo did go through one winter in my yard already. I did put some blankets over them, although on the tree the blankets didn't go to the ground, so luckily it survived my ignorance. :)

As for my zone, that is a whole different area of frustration for me. I'm in Gilbert (southeast of Phoenix) and nearly every zone map I try to read is different. I'm anywhere from zone 8-11! I finally settled on either one of the 9s or 10s, based on the BHG map that this forum linked me to from the preferences section, but that still makes quite a difference.

We had some temps down into the teens here, and I did not cover the irises. They were just fine. Irises are very hardy, tough plants. I don't imagine that your temp got low enough for it to be critical whether the blanket went all the way to the ground. But it's just something to keep in mind for the future. Another idea is to water before you cover plants because wet ground retains heat better than dry ground. Unless it is going to be very cold, though, I don't think this is critical either for you.

I think you would be the same winter hardiness zone as Phoenix. Arborday.org puts both areas in zone 9-10. There's very little you can't grow there as far as winter is concerned. The summer heat would be more likely to limit what you can grow. I'm in heat zone 8. Gilbert AZ is in heat zone 11. My brother lives in Glendale, and I vaguely remember that he used to grow his veggies during the winter instead of the summer.

Here's a link to the AHS heat zone map and an explanation of heat zones: http://www.ahs.org/publications/heat_zone_finder.htm

Hope this helps,

Karen

I'm not sure anywhere in the continental US gets into USDA zone 11, so I suspect the site where you found zone 11 was the heat zone map. Either that or I've noticed the BHG colors aren't always very distinct on their maps--I just went and looked at their one for AZ, and the brownish color they use for zone 9b is pretty much identical to the brownish color they use for zone 11, the only way to tell that you're really 9b and not 11 is to realize that the zones usually progress in order as you go across the state, and you can see that the brownish areas where Gilbert & Phoenix are in are just south of the greenish areas which are unmistakably zone 8, so it makes much more sense that you're zone 9b rather than zone 11. So I think you're in either 9a or 9b, Phoenix and Gilbert aren't labeled on the map and 9a & 9b both exist in close proximity to each other in that area of the state so it's hard for me to be sure. Here's the map I was looking at: http://images.meredith.com/bhg/pdf/gardening/hardiness/hzm_Arizona.pdf

ecrane3, thank you so much! Your reply was very helpful. That was the map I used, because it was the most detailed I've been able to find, but I did not realize that they colors lay out in order. The browns are identical which is exactly what was giving me fits. Thanks so much! At least now I have some point of reference when researching plants I may be able to grow. Thanks again!

I re-opened the map from ecrane3 and saw that the determining factor for zone 11 is an annual average minimum temp of 40 or above. So I just googled my town and those terms and found that for Gilbert it is 40.5 in December. So I guess that settles it- I'm zone 11! It does exist in the US.

Sorry, no way on earth you're in zone 11. The zones aren't based on your average minimum temps, they're based on what's the lowest temperature you can typically expect to see during the winter. If your average winter lows are 40, chances are you get down to temps that are lower than 40 on some days (just like it'll be higher than 40 on some days), so I'm standing by my previous assessment of zone 9a or 9b. I'm in 9a and my average lows are 37-38, so since your average lows are a couple degrees warmer that may put you in 9b instead of 9a, but it is certainly not enough to even move you to zone 10, let alone 11. For additional perspective, Miami FL which is still in zone 10b according to that website has average winter lows of 60, quite a bit warmer than you and they don't even quite make it into zone 11! I hope you'll believe me on this, otherwise you're going to end up very disappointed when you try to leave all your tropicals outside for the winter!

I just went to the map again and I think I know what was confusing you...when they say "average annual low", they don't mean the average of all the daily lows during the winter (which is where you're coming up with 40.5 degrees), they mean that they look over the last 30 or so years and look at what's the absolutely lowest temperature you hit in each one of those years, then they average those together to come up with the zones (after all, it's important that plants be able to tolerate those cold nights that you get, not just nights that are average).

ecrane3,

You are correct in that the "average annual low" refers to the one coldest temp in each year, and then those numbers are averaged together. But the number of years involved is much shorter than 30.

Personally, I think it should be over a longer time period. In my opinion neither 12 years nor 16 years is a long enough period of time to formulate this type of statistic. The USDA 1990 map, of course, is the one still most commonly quoted today. I've checked the coldest-temp for my area from the 1940s to the present, and the years used in the 1990 USDA map coincidentally happen to be much colder/more severe winters than the time period before that and the time period since then.

http://en.wikipedia.org/wiki/Hardiness_zone#North_American_hardiness_zones

"The USDA first issued its standardized hardiness-zone map in 1960, and revised it in 1965. A new map was issued in 1990, based on U.S. and Canadian data from 1974 through 1986 (and 1971-1984 for Mexico). While the 1990-issue map utilized approximately double the number of stations, it also divided the temperature-zones into five-degree a/b zones for greater accuracy. This revised map showed many areas to be suddenly colder than the 1960 map, due largely to a number of severely colder winters in the central and eastern U.S. in the 1974-1986 data-gathering period as opposed to the mid-20th-century data-sampling period used in the 1960 map."

"In 2003, a preliminary draft of a new USDA map was produced by the American Horticultural Society (AHS), compiled by Meteorological Evaluation Services Co., Inc. of Amityville, NY, using temperature data collected from July 1986 to March 2002. This was a period of warmer winters than the 1974-1986 period, especially in the eastern U.S.A., and thus the 2003 map placed many areas approximately a half-zone higher (warmer) than the 1990 map had. Many have noted that the map seemed to have drifted closer to the original 1960 map in its overall zone-delineations."

Karen

I read somewhere that they used to use 30 years of data but then in more recent years they've started looking at shorter periods of time but people are in disagreement about whether it's appropriate to use less years or not. Either way, no matter how many years they look at, there's no way Gilbert AZ is in zone 11.

They may have used 30 years for the original 1960 map that was revised in 1965. But the 1990 one only covers 12 years and the 2002 one covers 16 years, technically only 15 winters. Way too short a time period.

Nope, Zone 8b per USDA 1990 map. Might have picked up half a zone or a whole zone, 9a-9b, with the new AHS map. However, zone 11 does exist in the U.S. -- I think it's called Hawaii. ; - )

Still Bebekah should have no problem with those particular plants, except maybe covering the tangelo if a frost is predicted.

Karen