Keep in mind that first, the spores of the most common tomato diseases are also airborne so even if you were to use only some sort of sterile conditions to grow in, if the plants are exposed to the open air they can get infected. Thus the recommendation to begin fungicide sprays from day 1 of plant out.

Second, the spores can overwinter in some zones with mild winters but only on live plant tissue. Dead leaves, mowed and dried grasses wouldn't offer much life-support.

So is it 100% risk-free? No, but the benefits to the plants from all your mulch far outweigh any risks associated with using them.

Dave

Edited to add - we are talking fungus spores. Bacteria and the diseases they cause are a different matter.

This post was edited by digdirt on Thu, May 8, 14 at 14:15

This isn't really a tomato answer. There are (broadly) two sorts of mulch. Three, if you count shredded rubber and that dyed stuff from Scotts, but let's not right now. A wet flat mulch "coats' the soil and is much more active in all respects than dry airy mulch. The airy type does a bit better job of insulating the dirt from moisture loss and heat gain, and the first (yours) does a better job of composting itself sooner.

Since you know it's entirely possible that what you're now doing isn't working and is possibly causing you problems, then change things around by composting away from the plants and adding it in after breakdown, not before. What you use instead of that as a mulch is sort of a wide open topic.

Thanks for the replies! I have three beds of tomatoes, so I may try a different mulch in each of them and see of there is any noticeable difference. I'll continue to add leaves and grass to all of them in the fall, but use it as mulch in only one bed this summer. I'll try hay or straw in the second and wood chips over newspaper in the third bed.

I'd choose straw over hay. Hay can contain a number of different weed seeds that would just love to germinate in your nice rich soil. Cardboard under straw is awesome.
Edie