Because the mulch aids in holding soil moisture the soil under the mulch will be cooler than the same soil exposed to the hot sun, although the mulch material can also keep the soil cooler so that soil moisture is not evaporated. Keeping the soil moisture level up will help your plants uptake necessary soil nutrients as well as aid in keeping the plants roots cooler so they can transfer more moisture to the plants leaves reducing the plants need to transpire moisture to stay cool. Mulch should not slow down plant growth, if the soil is relatively healthy.

Here in zone 5, it's never really a problem. A heavy layer of mulch can delay the soil from thawing in very early spring, but other than that, the cooling effect is a good thing, not a bad one. In zone 9 I would think it would be even less of an issue.

-Diggity

I don't think mulch will slow much down in your zone 9. Here in zone 5 it will slow things down in spring because it keeps the soil cooler (frozen) longer. Not neccessarily slowing the growth down, per se, just delaying it.

tj

Cooler is very welcome here in my zone when summer sets in with days on end of around 100*+ or- and blazing, searing sun.
Birds fight over the bird bath which I rinse out and fill with cool water from the garden hose every day. They seem to thoroughly enjoy splashing around in the cool water.

That is when my soak hoses and mulch are worth their weight.
Bill P.

I put heavy amounts of woodchips around the top of several plantings and realized the same problem you have described. What I eventually thought was perhaps I was not getting enough water into the mulch to actually soak up the soil.
Dig beneath the mulch and check the moisture in the soil and another possibility is that the mulch is using up too much N as it decomposes at the soil level.
Keep trying. Mulch is good in the long run I believe :)

I use mulch in my rows to keep down the weeds. My garden is a little downhill, so the rows run parallel to the hill, and the lower rows are mounded up a few inches, in case of too much water. In those rows I brought the mulch up to a few inches of the base of my peppers. I noticed they grew slowly, and the bugs were chewing the leaves faster than they could make them. I poured soybean meal around these plants, and then used a 8 inch wooden dowel to make holes and drive the meal down to near the roots. In about a week, I noticed the peppers perked up, and they really have come on to make some really nice peppers. The point is I brought the mulch too close, forgetting it still needs to break down, and uses the surrounding nitrogen to do this, depriving the pepper plants of the nutrient. Real compost would have been ok to put near the base of plants, because it has 'rotted' to the point where it doesn't 'take', but leaves nutrients in the soil. That's my understanding of this process.

Think of organic mulch as a soil temperature BUFFER. It assists in protecting roots from sudden freezes as well as excess heat. Temperature excesses in either direction are not only a problem for roots, but for the soil biota that is essential for a healthy soil.

danny,

we've never found that mulch does anything less than help us to garden using less water at the very least, yes in those hot summers it cools the root runs which helps the plants as in winter it warms the root runs with the same effect.

len

Here is a link that might be useful: len's garden page

Denno, regarding wood chip mulch, I've seen the exact same thing. I love them as a compost ingredient, but I'll forgo them as a mulch in the vegetable garden. Other people have reported better results using wood chips as a mulch, but I just haven't seen it. It's different with trees and shrubs I think because they they are a lot more permanent than annual vegetables, and they will eventually use the chips to good advantage after the chips have broken down a bit. I think vegetables have a higher nutrient demand over a shorter life-span and any theft of nitrogen by the chips is enough to make them stumble. Too, wood chips shed water, which can be a real bother.

-Diggity

I can't speak to vegetable gardening but woodchip mulch has helped make a significant improvement with various flowers, trees and shrubs and did not hurt my pumpkin vines. On a number of occassions I saw the improvement relatively quickly. One recent example: At the end of winter/beginning of spring I mulched two old crabapple trees that were looking sad and they looked better this summer than they have in years. I also noticed that flowers that were mulched tended to do noticeably better than those that were not.

I have been on the vermiculture forum, but haven't yet gotten feedback (little pun there).
The foliage on my vegetables is beautifully green, but it seems the vegetables are not producing the way they used to - much less. It could be the timing - I grow everything from seed so my veg are slower coming than planting the little 6 packs. Shall I do a soil test with the little kit? The vegetables are summer squash and beans. The winter squash is great - The vegetables I do get are lovely, albeit a little bland when steamed. Is it the soil?? The worms eat our organic kitchen scraps, a little newspaper, and some coffee grounds sometimes. Thanks.