Don't dig the dahlias up. Just put down a layer of compost, wood chips, or bark mulch. There's no need to dig in the compost, just lay it on top of the soil and let the worms and critters incorporate it for you.

You are assuming covering the soil with compost will enable the water to be absorbed by the surrounding soil? I'm speaking of the soil surrounding the tuber in the hole. I plant my dahlias about 4- 5" down, cover with 1-2 " of soil and add soil as the stem gets longer above ground. I agree mulch should help but I still feel my soil is hydrophobic to some extent. Thank you.,

Where are you located and why do you think the soil is hydrophobic?

I agree that a thick layer of organic mulch and then watered deeply and slowly (like with a soaker hose run for an extended period - 18-24 hrs) should alleviate the issue. Also baby shampoo diluted in water acts a wetting agent and will reduce surface tension, allowing water penetration. Make sure it is baby shampoo or a non-detergent castille soap like Dr. Bronners so you don't add any unnecessary chemicals.

Or you can aerate the soil as well.

It is important to never allow the soil to dry so thoroughly that it becomes water repellent. Always keep it well mulched to reduce evaporation.

I agree mulch does keep in moisture and I am planning to mulch the individual plants once they are growing but they won't grow until I get the soil moist.

I am beginning to think that soaker hoses moisten soil better because they apply water SOOOO slow. I've always hand watered my plants but go back at least twice to fill the basin. Is that true that small dripping for a long time is better than hand watering which dumps more water all at once on plants?

I did just go out and buy $14 worth of agar-agar and I'd like to try it. I've read directions a couple of places and they do not mention how much of the agar-agar powder to use........

"Add boiling water to agar-agar powder to make a paste, add 1 cup of the paste mix into into 1 gallon of water. This will cover 43 square feet/ 6' x 7'.

I will be using 2 ounces of the agar-agar but if one was using more it seems like your dilution will change and could be much stronger. .......

I would love your answers to these questions!

Soaker hoses or drip tape irrigation would both work really well. Mulch the whole bed because you want the area around the corms to be soft and receptive to root growth.

You can try the agar. I doubt that it will work, but it has a neutral pH and is unlikely to do any harm anyway. Really, the only thing that permanently (or at least long-term) changes soil structure is the addition of organic matter.

Agar should break down pretty quickly in soil as its normal use is for growing bacteria.

Your best bet is a nice, thick layer of whatever organic material you can lay your hands on. I looked up agar for gardening online and found one guy in Australia who uses it. If it were a panacea, it would be a lot more popular. Organic mulch, OTOH, is well documented.

Agar is snake oil. Lots of mulch and low precipitation rate irrigation.

I'll take the advice to skip the agar-agar and mulch well after giving the soil a good watering with a soaker hose. Thanks for your ideas!

I mean the advice of several who said skip the agar-agar.

It makes more sense to water after mulching. The mulch should absorb and then release the water slowly, and it will keep the soil in contact with the damp and keep it from becoming hydrophilic. We have fairly dry conditions right now and you can put fingers into mulch and leaves and feel dampness immediately,barely an inch in. You can water before and after of course but watering after mulching will be much more effective and use less water. I think it's fair to say ground coverings of organic matter is a big part of nature's water retention mechanism.

I hadn't heard that before but it make sense, thanks!

Well it would have made more sense if I had written hydrophobic but hopefully you understood me.

"The mulch should absorb and then release the water slowly, and it will keep the soil in contact with the damp and keep it from becoming" hydrophobic.

^ This is my experience exactly, in desert conditions. Mulch keeps the top surface of the soil damp so it never becomes hydrophobic under there, and in fact the bottom layer of mulch becomes black and starts to decompose. The top layer of soil becomes richer in organic matter and everything improves, including the moisture situation. I find that even a very thin light mulch helps prevent the hydrophobic problem as well as the crusting that prevents tiny seeds from sprouting.

Dahlia tuber sprouts are so vigorous that it's not a problem to mulch them before they come up. You can try to leave a gap in the mulch over each tuber while mulching the whole area, or you can mulch the whole area and then every few days when you expect them to sprout, pull the mulch aside and if they are sprouting, poke some small space in the mulch for them to come up through. If your mulch is thin and loose enough they can poke their own way up without your help.

For mulch I use anything and everything that I can find. On new land I go out and cut weeds -- I can find clumps of single types of plants that have good foliage for mulch, either while they are green before they seed, or the dry golden stalks in winter. Once my garden is producing some stuff of its own, I find that the deadheading of the flowers, the cut down stalks and foliage of ornamentals, and the stalks of vegetables that I let go to seed provide almost enough mulch for my whole vegetable garden.

I ran my larger diameter soaker hoses for 12 hours last Friday and the soil was well moistened more than 6" down! I planted the tubers two days later and thought the soil was ok. I then covered with 2" of dry compost. I would like to moisten the compost, even at this point because it seems like it would do a better job of keeping it moist underneath.

I am guessing that I'm going to have to use the soaker hoses when I water every week, more often in 90 degree weather? Hand watering is so much easier for me and I was wondering if now that the soil is moist wouldn't hand watering be ok?

Thank you all for your thoughts on my problem.

Ginny

Turn the soaker hose on, set a timer. It doesn't get much easier! I have my drip irrigation under the mulch to protect it from the sun's UV and because it's ugly, but you can apply water above or below the mulch.

I don't grow dahlias, but I assume that they need regular summer water, more when it's hot. The amount of water that you will need to apply depends on temperature, humidity, plant type, and soil drainage. It will vary across the summer.