Get a good reliable soil test done from Clemson University Cooperative Extension Service,

http://www.clemson.edu/extension/hgic/plants/other/soils/hgic1652.html

Nutrient availability for most plants is best in the 6.0 to 7.0 pH range, although some plants, such as Gardenias, do grow better in a more acidic (5.0 to 5.5 pH) soil. The Veronica, Sedum, Phlox,, Iris, and most others do better with a soil pH in that 6.0 to 7.0 pH range.

Tilling an existing planting bed is not recommended since that could destroy the roots of existing plants. There is no need to remove any mulch that is there before adding more. If the soil in that bed has adequate amounts of organic matter the soil should not need any work to "loosen" it.

In addition to the soil test for pH and nutrient levels these simple soil test may also help.

1) Soil test for organic
matter. From that soil sample put enough of the rest to make a 4 inch level in
a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and
replace the lid, tightly. Shake the jar vigorously and then let it stand for 24
hours. Your soil will settle out according to soil particle size and weight.
For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the
bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above
that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole
1 foot square and 1 foot deep and fill that with water. After that water drains
away refill the hole with more water and time how long it takes that to drain
away. Anything less than 2 hours and your soil drains’ too quickly and needs
more organic matter to slow that drainage down. Anything over 6 hours and the
soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful
of your slightly damp soil and squeeze it tightly. When the pressure is
released the soil should hold together in that clump, but when poked with a
finger that clump should fall apart.

4) Smell. What does your
soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant
odor? The more organic matter in your soil the more active the soil bacteria
will be and the nicer your soil will smell, to a point. Too much organic matter
can be bad as well.

5) Life. How many
earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5,
according to the Natural Resources Conservation Service, indicates a soil that
is not healthy.

kimmq is kimmsr

Kimmq- Thank you for the information. I will certainly do the tests that you recommend.

Regarding the tilling, this isn't really an established garden, as there are only two plants, about 8-10 ft apart from one another (and after looking at it this morning, I realize the bed is closer to 30 ft long). Some areas are somewhat workable, but some are just plain ol' SC clay that I can't dig at all, so I'm going to have to do something to make the soil workable.

Do you know how far the roots to the gardenia and iris extend? I"m wondering if it is possible to till around them at a safe distance.

A shrub usually has most of its roots inside the 'drip line', i.e. the diameter of the top of the plant. You can confirm this by starting a couple feet outside that, dig a test hole one shovel deep, and see what you find. If you don't hit a lot of fibrous roots, move in a foot and see how it changes. I would avoid digging inside the drip line as a general rule. Keep in mind you may have tree roots from elsewhere depending on your landscaping. I've seen silver maple and cottonwood roots 20-30 ft. outside the dripline of the tree.

I second the idea of a good soil test. Unless the pH is way too low for what you want to plant, slightly acidic is OK and you don't risk harming the acid loving plants that are already there. Also, compost will help moderate pH and help nutrient availability even in pH or other soil conditions that are less than ideal.

If this is large and daunting, consider doing half this season and heavily mulch the other half with layers of leaves, grass clippings (mixed with other stuff so as not to mat down too much), wood chips, shredded yard waste, etc. It will start to improve the soil texture and fertility and will be easier to dig next year.

One other thing. Ignore all fungi (unless they're really really interesting like the green fluorescent slime I saw last year) and just dig them in to be part of the decomposing Battle Royal going on in the dirt. No harm. No foul.

Some fungi are good and beneficial in soils, as are bacteria, but some fungi are also disease pathogens and can create problems. It is not easy for most of us to tell the difference until the plants we are growing show signs of disease. Some fungi form symbiotic, or mutually beneficial, relationships with plants, ie. Mycorrhizal fungi, while others simply suck the life out of plants. There are also some that refer to slime molds as fungi but which are not.

kimmq is kimmsr

Balance your soil nutrients based on a reputable labs results and the corresponding agronomist's interpretation and recommendations. Most university labs, even those that charge, are inundated with soils to sample because they are so cheap or free of charge. The schools also tend to have students executing the analysis and are encouraged to hurry them along. If the soil is too hard, too impenetrable to incorporate amendments without intensive tilling (not recommended anyway), then just plant your plants directly into the soil with compost added to backfill. Apply calcitic lime, fine (powdery) and granular, as a broadcast over the entire bed and water in lightly before ever planting. Then add the same mix into your compost and also some directly into the hole before backfilling. Your clay is most likely high in Mg making it tighter than it should be. Just a guess without knowing for certain with a reputable soil test. :-)

Changing a soils pH is not something that will happen in a short time, it takes months.

Incorporating organic matter in a planting hole will change the soils porosity so water cab flow into the hole easily but cannot flow out.

Soil testing labs are inundated with samples to test in the spring, because that is when most people think about doing that. The best time is in the fall which also gives the Soil Food Web time to work.

Lime, placed in the planting hole, can cause root problems because as it is wet the high pH of that lime would be too caustic fro those roots. You can get the same problem with any stone dust material or synthetic fertilizer. When using these materials they need to be well mixed into the soil before planting.

kimmq is kimmsr

In my opinion, you should till up this bed. Let me say why before everyone gets upset..... I, too bought a home several years ago with the same situation. Heavy clay based soil and neglected beds, with a few scattered plants surviving. I have a small "Mantis" type tiller that I used on everything... I laid down as much Compost as I could and tilled everything up.... going around the plants. I also broadcasted a slow release fertilizer based on my soil test results. Not only did this break up the clay and add organic matter but I got the soil Aerated,... which is what your soil needs. I did not lose a single plant or shrub from the tilling and I did till up to the dripline. Remember a little root disturbance can actually jump start a plant, you are not going to kill a plant by a little tilling. We disturb roots every time we transplant & divide a plant's root system, especially iris, they love being divided and replanted! You can just lay compost on the top and wait for the worms to help you.... but why not just do a quality soil make-over right now, I think you will be happy with the results

Thanks everyone for all your thoughts. I think we're going to try the tilling, and will till in the old pine straw and a truckload of compost mixed with aged cow manure that a friend is giving us, steering clear of the iris and especially the gardenia.

I have another question about pine straw. In a different bed in another part of the property, I did find a few spots where white fungus is growing under the pine straw. Should I just remove those spots or all of the pine straw from the (very large) bed? We have lost quite a few shrubs in this area from bacterial shot hole and a few from canker. There must be something about this location that is conducive to the breeding of pathogens.

There is something about it, its staying too wet. The lime mixed in with compost in the planting hole will not be too caustic but after rereading my post I should mentioned something even better than high ca lime for your situation, gypsum...

The white fungus is fine by the way, again assuming you balance out your nutrients, any "pathogens" will be sorted out by the "good pathogens". One fruit's mold is another man's penicillin... :-)

So we tilled the bed and mixed in a few inches of aged compost and manure from a friends farm. The garden is looking great and the plants are thriving- except for the iris, sort of.

The iris was doing great and bloomed beautifully. It is the hugest Siberian I've ever seen- at least 2ft diameter at the base and takes up a 5ft circle in the garden. After blooming it has flopped terribly. Last year the leaves cascaded elegantly the entire summer and fall, now even the center leaves are trying to lie on the ground.

When we tilled, my husband did get too close to the iris before I could stop him, and when we planted other perennials nearby, we had to cut many thick roots, which I assume were from the iris. So I'm wondering if root damage is causing the flopping, or if the monster just needs to be divided. I don't know how old it is, as the house and garden bed is new to us since last summer. I was under the impression, however, that Siberian irises don't really require division to maintain vigor.

The centers die out in mature clumps of Siberian iris, leaving a donut of vigorous peripheral growth surrounding a rather bare center. While they do not need dividing as frequently as say bearded iris, they do benefit from periodic division and discarding of the older, bare center growth.

Thanks gardengal. I don't really see any center bareness, just flopping. Hmmm...

Possibly too much nitrogen from all that manure made them grow long and lanky? Either that or the root cutting. I would leave them alone (they've been through enough already) and see how they do.

I hadn't considered the manure being an issue, thank you! I will let the iris be for now. It probably should be divided next spring for size anyway.