Starting fresh: Gardening in new subdivisions

Improving soil after construction damage

A new house in a new subdivision is an exciting major life event. Now that you’ve moved in, you can’t wait to plant and cultivate the yard of your dreams.

But what if your soil is poor? Typically, the existing thick topsoil layer is removed before construction and once building is complete, they top it with a just few inches of topsoil. Beneath the topsoil is subsoil which is often a heavier clay or a mix of materials which contains very little organic matter. Chances are, the area is very compacted, the result of heavy equipment needed to build your fine new house, making matters even worse. Compacted soils have poor drainage making it difficult for roots to penetrate and spread, and provides little oxygen needed for plant health. Both the top soil and subsoil has had a lot of disturbance which is not good for soil structure. Sound familiar? The good news is that you can fix your soil.

Your best bet is to adopt a no till system for flower and veggie beds. That means absolutely no rototilling, which only makes soil issues worse. Start by top dressing your beds with an inch or two of compost. You can mix it in a bit by hand if you want but you’re much better off leaving it on top and letting soil organisms do the work for you.

Next you will absolutely need to mulch. What you use for mulch will depend on your budget and timeline. Leaf mulch breaks down quickly and it’s free. Ask friends and family living in leafy mature areas to donate their bags of leaves. Advertise on social media sites for donations. How much do you need? As much as you can get. Use a lawn mower to shred the leaves for even quicker breakdown before laying it on top of your soil. A thick layer of shredded leaves 12 to 30 centimetres (5 – 12 inches) breaks down in a surprisingly short period of time. No need to mix it in. And remember to top it up every growing season.

Shredded wood mulch is also a great option. While it takes longer to break down and improve your soil, there are other benefits to shredded wood mulch, namely weed control. Shredded wood mulch is the mulch of choice for heavy clay. Never use landscape cloth under mulch. It is not needed and negates the benefits to your soil. Mulch in any form should be at least 10 - 12 centimetres (4 – 5 inches) thick and should not be mixed into the soil (especially shredded wood mulch) or you run the risk of tying up nitrogen in the soil.

How long does it take to improve soil? It depends on the severity of the soil problem, but as long as you are not working your soil and mulching faithfully, give it at least two growing seasons if using leaf mulch and as long as three years if using shredded bark mulch. Mulch adds organic matter to your soil, but more importantly, changes the structure – or the way that soil holds together – for the better. While clay soil will always be clay, improved structure will make it lighter and crumbly and plants will thrive in it.

Whatever you decide to do with your soil mulch wise, never add sand to “improve” it. This is very old and very bad advice. We’ve learned that with clay soil, the less you work it the better. Compost, mulch and no till are really the best approaches to improving soil. Never work soil when it’s wet either. When planting trees, don’t amend the planting hole or you’re creating texture issues which will interfere with root development and water movement. Just lay compost and mulch on top.

Until your soil improves, select plants carefully. Choosing plants to suit your site is always good advice. With poor soil, select trees, shrubs and perennials which are not fussy about poor drainage and heavy soils. While you’re at it, make sure that the light conditions are correct for your choices too.

If you need a quicker fix for your soil problems, consider installing raised beds. You can build frames for raised beds out of wood like cedar or spruce. If you have the budget, interlocking blocks are very attractive too. Raised beds should be at least 15 centimetres (6 inches) tall but may be taller. You will need fill raised beds with topsoil which can be purchased in bulk from a landscape store. The stuff you buy in bags at big box stores calls itself soil but it has no mineral particles in it and is largely peat moss. This is not suitable for permanent raised beds for a number of reasons so make sure you get real topsoil.

Not convinced your soil will improve with the no-till and mulch method? Do an experiment. Select an experimental bed to mulch according to our instructions and leave it alone. After two full growing seasons, push aside the mulch and examine your soil. Compare this soil with an area that was not treated (un-mulched and/or tilled). What do you see? The no-till, mulched soils will be crumbly and a richer colour. You should be able to dig in it with your hand alone. Dig a small hole and pour water into it. It will drain more quickly than one in the untreated area.

For more reading see:

Mulch and more: a how to guide for healthy yards

How to plant a tree

Planting practices that harm trees and shrubs