Wednesday, October 1, 2014

Use leaves to stop weeds

Oak leaves covered with pine needles to keep them in place

Leaves are starting to fall, and they are way too useful to just rake up and put on the curb for pickup.  It’s also a lot of work to rake them out of your shrubbery and flower beds.  Leaves are natural mulch that feed soil and stop weeds, and the thicker they lie, the better they do it.  A foot of mixed leaves can grow great vegetables. They belong on bare soil and mulched beds. 

Leaves laid thick for growing vegetables

Leaves need to be removed from buildings, pavements and paths.   They should not lie too thick on lawns, where they can smother grass, but even there, they can suppress crab grass and other small seeds, while stronger perennial grasses like fine and tall fescues, can grow right through several inches as the soil warms in the spring; they are encouraged by the fertility.  Larger annual grasses, like cheat and fox tails, need a good two inches to stop them.
Most small seeds need a touch of sunlight to allow them to germinate, lest they sprout too deep and are unable to grow out from under their cover.  The larger the seed, the more food it has to grow through soil or leaf cover.  But the smaller the seeds, the more there are to sprout.  Once larger seeds have sprouted, it can be easier to smother them with mulch, if they are covered before they put a lot of food in their roots.
Naturally fallen Red Maple leaves stopping bitter cress and annual rye

Leaves vary in their ability to stop weeds from sprouting.  Very soft light leaves, like box elder, can be eaten by worms, pill bugs, earwigs, and other detritus eaters before fall is even over, and are good for feeding soil, but are fairly useless for stopping weeds in the spring.  Not-so-soft leaves, like red maple, will make it through the winter and stop early spring weeds like groundsel and bitter cress.  Tougher leaves, like oak, sweet gum, and magnolia, stick around all summer, and prevent the germination of later-flying wild lettuce and dandelions and tracked-in crab grass.
Non-broadleaf evergreens also vary in their ability to stop weeds.  Pine needles and needle-type true cedars are tough and take a long time to decompose, but their shape allows seeds to grow through unless they are over an inch thick.  Flatter evergreens, like fir and local cedars, decompose more quickly, but seem to stop weeds fairly well anyways.
One kind of soft leaf can stop weed seeds smaller than a maple nut all summer, even after they are gone: black walnut.  They have juglone, a natural pre-emergent herbicide.  They are not a problem for established perennials, but they stop smaller seeds even after the soil is bare.  Spread under a tree where birds perch, they can stop blackberries and other berry seeds from sprouting where they are laid at least an inch deep.
Use leaves; don’t lose them.  They can save you a lot of work.

October issue, online at, sold at the Mail Center, 305 NE 6th St. 
Gardening is easy if you do it naturally.  Litter is tagging, marking the territory of the disorderly.

Rycke Brown, Natural Gardener                 541-955-9040