Every year some gardening challenges are absolutely predictable here in southern B.C. Weeds germinate in spring, there are long weeks of drought in summer and winter brings chilly nights when some plants may die without protection. Throughout this time there's always some plant that needs feeding.

That's why mulching is one of the best investments we can make. Organic mulching replenishes the soil in the same way that nature does. It attracts earthworms, holds on to moisture, suppresses weeds, helps fertilize soil and cools it in summer while warming it in winter.

One of the most useful mulches for flower beds is composted bark mulch. It's not especially nutritious, but is relatively neutral and fine enough to fit snugly around delicate plants. People with tiny gardens can buy it in bags while large-scale gardeners can get truckloads.

How well it suppresses weeds (as with all plant-based mulches) depends how thick you spread it. Another factor is how tall the plants are in that area. Two inches (5cm) is a good starting point for mulch: thicker spreads can sometimes be left for several years. But perennial weeds (like dandelions and dock) must be removed completely or they'll re-grow every time.

Some gardeners use mushroom manure. It can have considerable food value, but this varies and so can its alkalinity. It's usually far too alkaline for acid-loving plants like rhododendrons or blueberries. Most mushroom manures are not organic.

Straw can be a good mulch for taller crops in vegetable gardens-unfortunately most straw has lots of weed seeds.

Hay usually has even more.

Leaves, especially when shredded into leaf-mould, are a wonderful, free mulch for flower or vegetable gardens. In shrub gardens, you can deposit leaves as you rake them in fall. But they break down faster if shredded.

Dumping them in a garbage container and running a weed whacker over them is one useful way of shredding them.

Grass clippings are full of nitrogen for vegetable gardens and do a great job of suppressing weeds and attracting worms. But they get very hot when piled, so should be kept thin around tender seedlings.

In early to mid spring they can attract slugs and then susceptible seedlings need protection. But by summer when watering becomes necessary a grass mulch is a life-saver for the plants.

Living mulches are sometimes used by organic gardeners. White Dutch clover is one. This is the same clover that is found in some lawn mixes because it's a legume that fixes nitrogen in lawns.

It makes a low-growing path that needs very infrequent cutting.

I have seen gardeners mulch paths through veggie gardens with crop debris.

The paths I saw included pea vines, bean vines and corn leaves and stalks chopped small.

Alpine gardeners often use gravel and small stones or rocks as mulch. Sand with nutritious material underneath can apparently also be used in very dry climates.

Closer to home, landscape fabric can suppress non-perennial weeds while black plastic is sometimes used by gardeners to prevent soil compacting in winter.

? Anne Marrison is happy to answer garden questions. Send them to her via amarrison@shaw.ca.