Seasonal Maintenance Of Your Raised Bed Garden Soil

The purpose of this post is to help you get an idea of some of the things you can do throughout the year to keep your soil in great shape.

Your soil is slowly but surely being “worn down” by the effects of the elements and your plants themselves, which are consuming all of the good “nutrition” they can find in your soil.

It is up to the gardener to organically replenish the soil, and this is best done in a slow and steady fashion throughout the year.

Let me summarize these tasks first, before I go into greater detail:

In Late Fall

  • remove the tops of any plant material leftover from the growing season, leaving the roots in the soil
  • bring the soil level of your raised bed back up to where you want it by adding compost
  • cover your soil with non-woody mulch (like shredded leaves) or a cover crop for the winter

In Early Spring

  • till in or shear cover crop a couple of weeks before planting
  • (optional) remove mulch or cover your beds with clear plastic sheeting to speed the warming of soil
  • lightly till in or sprinkle some slow-release organic fertilizer on soil surface and cover with compost

During the Growing Season

  • periodically replenish your layer of mulch or compost to keep it 1 to 2 inches thick or use cover crops as needed
  • apply organic foliar sprays to your crops

In Early Fall

  • (optional) remove mulch to warm soil and extend growing season
  • lightly till in or sprinkle some slow-release organic fertilizer on soil surface and cover with compost

 

Now I’d like to cover these seasonal chores in more detail…

Late Fall

Let’s start our soil maintenance at the end of the growing season.  It is a good idea to remove the tops of any plants left over from the growing season, shred them and throw them (if not diseased or moldy) in the compost pile (but leaving the root masses to break down naturally – feeding your soil, leaving the structure of the soil intact, and aiding in aeration).

If your raised beds are fairly new, you can expect the soil level to drop by a few inches every year for the first few years as the topsoil/compost mix you initially filled the beds with slowly settles and the organic material breaks down.  I have certainly seen this in my own raised beds.  So your first major job is to “top off” your beds.

The Dirty Truth About Your Soil

Keep in mind that the primary advantage (horticulturally speaking) of a raised bed garden in the first place is the quality of the soil mixture inside it – possessing a loose and friable structure, rich in organic matter and nutrients, and elevated for drainage and the extending of gardening seasons.

Organic material is constantly decomposing and being consumed by your plants, so it needs to be replaced on a regular basis.

To bring the level of soil back up to the desired level (remembering to leave a couple of inches for a mulch of some kind, unless you are cover-cropping), simply add in more compost or topsoil and compost in a 50/50 mix (or whatever your preferred soil mixture is).

Different experts have their own “recipes” of  the best soil mix to fill a raised bed with (including certain proportions of peat moss, horticultural vermiculite, topsoil, blends of compost, worm castings, etc.), and I would leave this up to the individual gardener to experiment with, taking into consideration the specific needs of your own gardening environment.

Thank You Very Mulch

Once the soil mix in the bed is brought back up to the desired level, you are left with the choice of mulching or planting a cover crop.  Again, different experts give different advice here.  The one thing that I think it is safe to say that they all agree about is to at least cover your raised beds with some kind of mulch (1 or 2 inches deep) or cover crop, pretty much year round and especially over the harsh winter and summer seasons.

Let’s discuss mulch first.

Remember that anytime your garden soil is exposed to the sun and wind, you can expect to lose some soil nutrients (and certainly moisture) to the air.

Feed Your Local Earthworms With Mulch (and they will repay you)

By keeping the bed mulched with something organic and non-woody (such as straw, shredded leaves, or pine needles – but not wood chips or bark, which rob the soil of nitrogen as they break down), you can convert that nutrient loss into nutrient gain by the slow “cold composting” of those materials and the activity of earthworms (which distribute castings, the greatest soil amendment in the world, down into your layers of garden soil as they consume those materials).

A physical mulch (or cover crop) also protects your soil from erosion and the leaching of nutrients down through your soil (beyond the root zone) during heavy rains.

As an aside, some experts consider a couple of inches of pure compost (by itself) as the best mulch of all.

For the harsh winter and summer seasons, however, I think all garden areas should be covered (at least lightly) with a physical organic mulch of some kind (or cover crop).

Free Mulch, Falling From The Sky

My favorite mulch at this time of year is shredded leaves that I collect with my mulching mower.  They are free, non-woody and organic.

Just make sure you collect them from areas that have not been chemically treated and don’t use leaves that are diseased or from the following plants (which contain natural toxins): black walnut, eucalyptus, oleanders, and poison sumac.

Cover Crops

You may choose to plant a cover crop (instead of spreading mulch) at three distinct points during the year: fall, early spring or summer.

Also called “green manure“, cover crops (just like mulch) protect your soil from exposure and heavy rains, increase your soil’s water-holding capacity, suppress weeds, aerate the soil with their roots, encourage earthworm activity, and some even pull nitrogen from the air and “fix” it into your soil via their roots.

There are several varieties of winter cover crops (that you plant in early to mid fall) to choose from, including: various clovers, Austrian winter peas (I have had great success with this one), winter rye, winter wheat, oats, and hairy vetch.

Cover crops can be handled in a couple of ways when you are ready to clear them from your beds to begin regular garden planting.

They can be tilled in (at least a couple of weeks before you want to plant so that they have a chance to dry out/decompose a little) or if you follow a “no-till” strategy (which maintains the established soil structure) you can simply shear off the tops of the plants (with a mower, weed eater, hedge pruners or simply a rake), let them dry out on the surface for a couple of weeks and then plant your regular garden amongst the biomass (which simply becomes part of your mulch).

 Late Winter/Early Spring

During the period of late winter/early spring, if you used mulch instead of a cover crop to protect your soil and you are just itching to get your garden started, you may want to pull this mulch off of your raised bed so that the sun can warm the soil enough to start planting (especially in colder regions with short growing seasons).

Instead of completely removing the mulch, you might just want to open up certain areas.  You might also choose to cover your bare beds with clear plastic sheeting (solarize) for a week or two in late winter/early spring to really warm up the soil quickly.

Early spring is also a good time to sprinkle some slow-release organic fertilizer onto the surface of your raised beds and cover with a thin layer of compost and mulch (or lightly till it in to the top couple of inches).

 The Growing Season

During the growing seasons of spring, summer and fall, the only raised bed maintenance chores (outside of caring for your plantings with organic foliar sprays) involve keeping plenty of fresh mulch applied.

Again, I recommend non-woody mulches such as shredded leaves (or pure compost) that will feed your local earthworms – they will multiply their numbers and repay you with castings and soil aeration!

Also, if one of your raised bed planting areas becomes vacant for whatever reason during the growing season, you may want to plant a summer cover crop to protect and enrich the bare soil.  Some common ones include: buckwheat, Sudangrass, cowpeas and sorghum.

Early Fall

Finally, in early or mid fall, you may want to help extend your growing season by removing any mulch to let the sun warm the soil surface.

Also, fall is the second-best time (next to early spring) to apply a slow-release organic fertilizer to the surface of your raised beds (cover or lightly till in).

 Conclusion

Remember that your soil is the foundation of your garden, and keeping it in prime condition will make your plants stronger and less susceptible to a variety of diseases and stressors.

Your soil is constantly being worn down, and it is up to you to maintain it.  This is best done slowly and steadily, in a routine fashion as the seasons change.

 

 

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