The speed with which microbial activity makes the nutrients in vegetative matter you might mulch with available for plant uptake is Dependant in part of what percentage of the mulch is in contact with soil. If you have a thin layer of mulch atop the landscape fabric, the mulch will dry quickly & the amount of contact with microbe rich soil and humus would be reduced, so breakdown would be slower. If the mulch is placed above a layer that is situated above the landscape fabric and deep enough that microbial activity is plentiful, it will make much less difference. Microbes do not travel through the fabric to dinner each day. They dine where they live. If the upper layer is conducive to good microbial numbers and remains moist, breakdown will take place, but at a somewhat slower pace than if it was in direct contact with soil.

Why not pull the fabric up, add your mulch or compost, and put it back down when your crops are planted next year?

Al

remove the fabric.

In general it is better used on pathways than in areas where crops are grown. It stops/slows biological activity in both directions. In pathways this is fine, even desireable, but in growing areas it is not.

Agree with Al and Username. Don't use landscape fabric.

Most people don't mulch vegetable gardens unless they use compost, shredded leaves or grass clippings. All of these will keep weeds down and also build up your soil. I wouldn't use bark or other wood chips, though. Cultivating the garden by hand gets rid of weeds and loosens the soil.

OK, I've made a few mistakes already! Thanks for your comments. I'll tear out the landscape fabric.

After my tomatoes are finished, what end-of-season maintenance is recommended for vegetable gardens? Do I add compost (or some other recommended matter) now or in the spring?

You can add compost now if you like. That way, it has all winter to break down and condition the soil.

However, if you get your soil tested (at you local extension service), you will find out exactly what you need to add for optimum soil health for what you want to grow.

By all means, pull up the fabric when the tomatoes die back.
Sounds like that is the only 'mistake' you made.

When the tomatoes are finished bearing fruit (at first freeze), break up the plants and mow them down. Leave the clippings to mulch the soil. Add leaves and other mulchable material from the yard or flower beds if you have them, but remember that seeds from weeds and flowers and grass should not be put in your mulch if you do not want them to seed out in the Spring. If you need it, you should add raw manure now so that it will break down during the winter and not burn plants next year. Use a spading fork or rototiller to get the mulch into the soil so it will break down faster, per Tapla's post. You can wait until the Spring to add compost or composted manure, or you can add it now.

If your soil is already rich, then you shouldn't need to add compost or manure, but your own mulch will help keep the soil loose and rich in nutrients.

Best wishes,