Guides

The techniques that apply to every plant in the database

Most gardening advice is written per plant, which hides the fact that a small number of techniques account for nearly all of it. Watering, planting depth, pruning timing and soil handling are the same skills whether the subject is a tomato or an oak, and getting them right removes most of the problems that later get diagnosed as pests and diseases.

This section holds those techniques. Anything genuinely specific to one species lives on that species entry instead, because it is a fact about the plant rather than about the job.

Watering: deeply and rarely, not lightly and often

The single most common mistake in gardening is frequent shallow watering. It wets the top inch, encourages roots to stay at the surface where they dry out fastest, and keeps the surface permanently damp, which is what fungus gnats, damping off and several fungal diseases need.

Soak thoroughly, then wait until the top two inches are genuinely dry before doing it again. Check with a finger rather than a schedule, because a plant needs water at a different rate in July and January and the calendar does not know that.

Water the soil rather than the foliage, and do it in the morning. Leaves that stay wet overnight are the condition almost every fungal disease is waiting for.

The numbers behind that principle are worth having, because how to water plants correctly is mostly a question of how much and how deep rather than how often. Most beds want roughly an inch of water a week including rain, and an inch soaks six to eight inches down in average soil, which is where the working roots are. A light daily sprinkle wets the top inch, and the plant responds by keeping its roots in the layer that dries out first.

Checking costs nothing. Push a long screwdriver into the bed: it slides easily through moist soil and stops where the soil is dry, which tells you how deep the last watering actually reached. Do that once after a watering you thought was generous and the result usually changes how you water for good.

• Water early in the morning. Foliage dries as the day warms, and evening watering leaves leaves wet overnight, which is the condition most leaf diseases need.
• Water the soil, not the plant. Wet leaves lose water to evaporation and gain nothing, and the roots are what drink.
• Go slowly on clay and on any slope. Water applied faster than the soil can take it runs off, and a bed can look watered while the root zone stays dry.
• Mulch two to three inches deep. It cuts evaporation enough to change how often you have to water at all.
• Rain gauges are cheap. Counting rain against the weekly inch stops both of the common errors, watering a bed that does not need it and skipping one that does.

Planting depth, which is decided once and permanently

A woody plant set too deep does not die outright. It sits, fails to grow, and declines slowly over years, which is why the cause is so rarely identified.

• Trees and shrubs: the root flare, where the trunk widens into roots, stays visible at the surface
• Perennials: the crown sits at soil level, not buried
• Bulbs: depth is species-specific and matters, from three inches for a dahlia tuber to eight for a lily
• Tomatoes: the exception that proves the rule, because they root along a buried stem and are planted deeper on purpose
• Grafted plants: find the union first, because whether it goes above or below soil decides which plant you end up with

Pruning: the timing matters more than the technique

Almost every complaint about a shrub that stopped flowering is a timing problem rather than a cutting problem, and it comes down to one question: does the plant form its flower buds on old wood or new?

Plants that bloom on last year's wood, such as lilac, forsythia, azalea and bigleaf hydrangea, are pruned straight after flowering. Cut them in autumn or late winter and you remove the display you were waiting for.

Plants that bloom on the current season's growth, such as panicle hydrangea, butterfly bush and most roses, are pruned in late winter, and cutting them hard increases the flowering rather than costing it.

Two rules cut across both. Maples and birches bleed heavily from spring cuts and are pruned while dormant. Conifers, and lavender, do not regrow from bare old wood, so a cut past the green is permanent.

Set out as a pruning guide by plant group, with the cases the two rules above do not cover, it looks like this.

If you do not know which group a shrub belongs to, watch it for a season. When it flowers tells you when to prune it, and a year of waiting costs less than a year of no flowers.

The three cuts that solve most problems

Most of the pruning a home garden actually needs is removal rather than shaping, and three cuts cover it.

• Dead, damaged and diseased wood comes out at any time of year, on anything. This is the only pruning with no season attached to it.
• Crossing and rubbing branches: take out the weaker of the two, before the wound they grind into each other becomes a way in for disease.
• Thinning to open the center: removing whole branches back to their origin lets light and air through the plant, and airflow prevents more fungal disease than any spray treats.

Two rules apply to every cut. Cut back to a bud or to a branch, angled just above it, so no stub is left to die back. And never cut a tree back to stubs across the top, which is called topping: it produces weak regrowth from the wound, invites decay into the trunk, and cannot be undone.

Soil, which decides more than any product

Find out what you actually have before buying anything. A jar of soil, water and a day of settling separates sand, silt and clay, and that answer changes every watering and feeding decision that follows.

For clay the answer is organic matter added annually, not sand, which does not change the texture and can make the soil harder to work. For sand the answer is also organic matter, for the opposite reason: it holds the water and nutrients that otherwise drain straight through. Almost every soil question ends in the same place.

Timing is part of the job, not a footnote

Most garden jobs have a window, and doing the right thing in the wrong month is often worse than doing nothing. Dividing perennials in high summer costs the plant a season. Planting bare-root stock in leaf usually kills it. Feeding a shrub in late summer pushes soft growth into the first frost.

Where a job has a window, the guides give it as a month range and say what happens outside it, written for zone 6. Shift roughly two weeks earlier for each zone colder and two weeks later for each zone warmer.

Feeding: how to fertilize plants without guessing

Fertilizer is where the most money is wasted in a garden, and where the most damage is done by good intentions. The starting point is that fertilizer is not plant food. Plants make their own food from light. Fertilizer supplies mineral nutrients, and adding more of a nutrient the soil already holds does nothing useful and sometimes does harm.

A balanced product such as 10-10-10 or 5-5-5 covers general garden use. The numbers are percentages by weight, which makes the arithmetic simple: to apply one pound of actual nitrogen per 1,000 square feet using a 10-10-10, you spread ten pounds of the product, because ten percent of ten pounds is one pound.

• More is not better. Excess fertilizer is a salt, and salt pulls water out of roots. Scorched leaf edges on a well-watered plant are usually a feeding problem rather than a drought one.
• Never feed a drought-stressed plant, a dormant one, or a newly planted one with damaged roots. In all three cases the plant cannot take the nutrients up.
• Stop feeding woody plants by late summer. Nitrogen late in the season pushes soft growth that does not harden before frost, which is how winter damage happens to plants that are hardy in your zone.
• Get a soil test before buying anything containing phosphorus. It is the nutrient most often applied unnecessarily and the one most likely to end up in waterways.
• Organic and synthetic differ in release rate rather than in quality. Organic sources release slowly as soil organisms break them down, which suits established beds. Synthetic acts immediately, which suits a diagnosed deficiency.

Overwintering: the jobs that belong before the ground freezes

Winter damage is mostly not about the coldest night. It is about roots that went into winter dry, bark that thawed and refroze, and containers that had nowhere to put the cold.

• Water everything deeply until the ground freezes, evergreens especially. They keep losing water through their leaves all winter and cannot replace it from frozen soil, which is what winter scorch actually is.
• Mulch after the ground has cooled, not before. Mulching warm ground keeps it warm and delays dormancy; mulching cold ground holds the temperature steady, which is the point of doing it.
• Put trunk guards on young trees before the first snow. Voles work under snow cover and rabbits work above it, and a girdled trunk kills the tree the following summer with no warning.
• Move containers to a sheltered spot, against a wall or grouped together. Roots in a pot are roughly one to two zones less hardy than the same plant in the ground, because there is no soil mass around them.
• Leave the perennials standing. Cutting a bed to the ground in fall removes the insulation over the crowns and the seed heads that feed birds, and the stems come away easily in spring.
• Do not wrap plants in plastic. Sealed wrapping traps moisture and cooks the plant on the first sunny day. Burlap screens against wind, which is a different job with a different material.