Why Do "Full Sun" Plants Wilt in the Sun?

Many perennials I planted in the spring are supposed to like full sun, but are planted in a location that gets an hour or so of direct morning sun, then direct sun from 12pm to 3pm. So, they get about 4 hours of total direct sun and the rest of the day it is filtered sun or full shade. They receive at least an inch of water a week, and sometimes a little more during the weeks of high temperatures and drought. So, why do they always wilt in the afternoon sun? Of course, they bounce back once the shade comes. (I water at the base of the plants, too.) I can’t imagine what would have happened if I had planted them in 6+ hours of direct sunlight as the directions suggested. It is depressing when I only get to enjoy certain flowers once they are in the shade or on overcast/rainy days! Not to mention when people come to visit and want to see my garden and ½ of the plants are wilted because it’s between 12pm and 3pm! The perennials that did this are Super Aster Daisies, Gaillardia Oranges and Lemons, Butterfly Blue Scabiosa, Dwarf Asters, and Gerbera Daisies. In a separate bed with full sun from 10:30am to 3pm, the Oriental Casa Blanca Lilies would wilt, but bounce back once in shade. At first, I thought I wasn't watering these plants good enough, so gave them some more water. Then on a few days when I saw them wilting and didn't give them more water, I noticed they perked back up once the shade came. So, I quit watering them just because they were wilted, and just gave them 1-2 inches a week depending on the weather conditions. Any idea why this happens and if I can prevent it? I live in Zone 8b, coastal South Carolina.
Thanks!

The afternoon sun is the hottest of the day. Also, maybe they are getting a bit TOO much water. Try cutting back on watering a bit.

In a climate like yours where the summers are warm, spring planting often doesn't give plants enough chance to get established before summer heat hits, so you will often notice some wilting during that first summer. By next year they should be better established and you won't see as much wilting.

Also just because you see wilting doesn't necessarily mean they don't have enough water--with plants that aren't fully established, sometimes their root system is not sufficient to take up water fast enough during the heat of the day, so they will wilt but then perk up in the evening when the sun is gone and things cool off which sounds like what's happening with yours. Because of that I would be careful on the watering--do the finger test to see if the soil a few inches down is still wet before you decide they need more water, otherwise to tommy's point you could end up overwatering.

Thank you both for the replies. Ecrane3, I have read a lot about plants getting established, but how does one know when establishment has taken place? Would it be safe to assume that by next spring these plants will be established? If I plant something now (Hosta, Astilbe and Salvia,) do you think they would be established by next spring?

I am thinking that I have actually under watered many of my sun plants. After having watered plants in the morning, I had to move one elsewhere, which I decided to do in the evening. After transplanting it, I went to check the soil of its former hole and noticed that the top 2 inches of soil were moist, but it became drier and drier the deeper I dug. I stopped digging after about 12 inches lol. However, the soil at 12 inches of depth appeared that I hadn't watered in months and I am a faithful waterer especially in the heat of summer!

I researched quite a bit on plant care and have learned so many things, but I guess I must have took the "DO NOT OVERWATER" warnings way too serious! So, now I have some further questions to ask.

1. What is the best way to "water deeply" without a soaker hose or drip irrigation system?
2. How do I know when I've watered deeply?
3. When I start watering at the base of a plant, how far out do I need to "water deeply"?
4. Without rain, how much water do I supply the plants to know that I have watered enough? I had been thinking that a gallon or two (depending on the size of the plant) was enough, but apparently I was wrong!

Thanks!

1. What is the best way to "water deeply" without a soaker hose or drip irrigation system?
I walk around with the hose and spray the thirsty plants, at the base, not the foliage.

2. How do I know when I've watered deeply?
If plants are turgid the next morning, they have sufficient moisture. If you are still unsure, dig around a bit after watering to see how deep the moisture has gone. If it's not what you consider deep enough, add more water.

3. When I start watering at the base of a plant, how far out do I need to "water deeply"?
Under the canopy of the plant should be sufficient.

4. Without rain, how much water do I supply the plants to know that I have watered enough? I had been thinking that a gallon or two (depending on the size of the plant) was enough, but apparently I was wrong!
This depends on what plants you have, their size, the composition of your soil, the amount of wind and direct sun, how long it has been since water was added... impossible to say really. The water could be running away sideways instead of soaking down.

If you water too much/often, the roots can rot and create a situation that looks like the plant is dehydrating to death - because it is if the roots have rotted and can't supply water to the plant. You may need some mulch to help retain the moisture.

If it's not wilted in the morning, a plant doesn't need water. A plant that is wilted at dawn is truly thirsty.

Thank you for your reply, purpleinopp! First, I have to tell you it is nice to meet someone from Opp, Alabama! That place has a special place in my heart and I have such fond memories of visiting my grandparents there every year when growing up. Both my parents attended Opp High School on Spurlin Street where my grandmother lived on the corner house across from the school. We always ate at the Blue Flame Grill! My great aunts, the Rainer Twins, still live there. Beautiful place!

Anyway, thank you for explaining the whole "watering" situation. Who knew watering flowers could be so complicated! I have decided to build a tiny mounded circle around each of the plants, so the water doesn't accidentally run off and goes where it is needed most. Again, thank you for answering my questions.

Glad to help. You'll get "better at it" as you gain more experience. And hopefully it'll just RAIN!

That IS cool that you know Opp. I haven't lived here long but also visited family here periodically throughout my life. The Blue Flame changes hands often but I'm told the menu is pretty reliable. I hadn't realized until reading your post, but it sounds like what used to be the high school is now the middle school, bordered by Spurlin St. on one side, right by the stadium. Did you ever eat at Benton's? The HS is caddy-corner from that now.

If you ever come for a visit, I'd love to say hi and show you my garden. You don't want to miss Opp Fest later this month, do you? The best part, a burn-out contest, isn't even mentioned in info link below.
http://www.alabama.travel/events/opp_fest_2010_-_web_submission
http://www.youtube.com/watch?v=Coty1OuSStI 2011 burnout
http://www.youtube.com/watch?v=5_rnAOFTmL4 2009
Can't find a vid from 2010

Sometimes also, if you amend your soil A bit so that moisture can go deeper you may find it helpful, and help the plant be able to use the moisture you are giving it. Compacted soils, soils that are too fine, etc, tend to shed water away from where you want it to reach. Wilting- as mentioned can be reduced by ' establishment' but it is a natural way for the plant to conserve itself.

Excellent point, kittriana!

I'm not physically able to do a lot of heavy work like double-digging and I can attest that adding organic matter to the surface will improve the soil underneath over time. Fallen leaves in the fall, occasional additions of cut grass from the mower bag throughout the summer, compost added whenever ready (and not too much plant mass in the way.)

While waiting for that to take effect from the top-down, I usually have to "prime" the dirt under really thirsty plants before it will accept significant water. Like, if a certain area has 5 plants that need water, give each one a little dribble, then go back to the first one to add a little more, switching from plant-to-plant often so the water has a few seconds to soak down instead of run sideways.

This also helps keep weeds to a minimum, allowing spots with no desirable plants to remain parched. I don't own a sprinkler, that kind of watering causes more problems than it solves.

Kittriana, I have amended the soil with Black Kow compost and added several bags of soil conditioner this month, so hopefully the plants will be able to absorb water better next summer, as well as, to avoid soil compaction.

Purpleinopp, it is a good idea to "prime" plants when watering. Unfortunately, I learned it too late in the growing season. However, I will definitely do so next growing season!

Regarding "priming" plants with water, you said:

"This also helps keep weeds to a minimum, allowing spots with no desirable plants to remain parched."

For me, this also reduces the area of soft, moist soil that attract the moles! (And my dogs!)

As for using fallen leaves for organic matter...that will be no problem at all. In fact, some of my garden areas will be covered in leaves as they sit very close to an oak tree and some other kind of tree that I haven't been able to identify. My question is when spring comes around, do I leave all of those leaves in the garden or rake some of them up? Or should I rake them up over the next month or so, chop them up with the mower, and then spread them out around the garden?

I've you've got the time and energy to mow and re-distribute them, they'll decompose much more quickly, releasing their benefits sooner.

I have the time and energy as do 2 of my teenage sons ha ha! If I use mowed leaves for mulch for this winter, how thick should I apply them?

Can't believe Opp High is now the middle school. During the summer, I used to go over and run all over the stadium and field. My mom grew up on Georgia Circle and when I visited my grandparents, we'd spend the summer at Opp Country Club; They golfed while I swam! If I am ever coming that way, I'd love to see your gardens!

Sounds cool! Anytime! Wonder if I was ever visiting my uncle's farm on Cool Springs Rd. while you were over there? Small world.

I put shredded leaves in pretty thick layers, 3-5". If you have leftovers after that, just put in compost pile, or a little thicker in spots where nothing's growing for winter. If it's too thick when you want to plant veggies or annuals, you can move some to compost pile. They're usually pretty much gone when I do it though.

I just bought 4 lavender plants at Lowe’s. They were in starter pots roots growing out the bottom holes and the dirt is soaking wet and soggy. Should I go ahead and plant them in the ground or should I just put all 4 in a large pot of sand potting soil and gravel mix. How can I dry out the roots to prevent root rot. I have read that lavender likes to be ignored as far as watering goes but boy do they wilt in the sun. Here’s what happened to the last lavender I planted in a container filled with styrofoam blocks sand and miticak grow potting mix and white rocks. Help. I love lavender but I’m confused sine the nursery doesn’t even treat it correctly and when I did it all died maybe it already had root rot starting. I don’t want that to happen to these new fellas.

purchased 'sun only' plants for Home Depot and Lowe's. I live in southern California
in rather hot zone - I think zone 9. All of the 'sun plants are wilting or dying. So sad
as did lots of work to establish my garden. Last week, I put down 3" of mulch to protect the plants from the hot soil, watered per package instructions. Checked the plants, all are very droopy. Used a moisture gadget and does show enough moisture, did this about 4"- 5" deep. Please let me know what I am doing wrong as do love my garden. Thank you, Bobbi
I surely would like to know what I am doing wrong as Love being a gardener