Every week, The Garden Soil Report, Harvest to Table’s weekly Substack newsletter, begins with a few numbers:

Soil temperature
Temperature highs and lows
Soil moisture (VWC)
Daylight hours

These numbers are not simply a record of what happened in the garden. They are a way of understanding what the garden is ready for now.

The most important number for planting vegetables is soil temperature.

The other numbers help you interpret it.

Table of Contents

Know What to Plant This Week

Every week I answer the gardener's most important question: what should I plant now? Get seasonal planting advice free — or go Pro for my full Soil Temperature Garden Report, with soil temperature, moisture, weather trends, and crop-by-crop recommendations.

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Air temperature tells you what plants will experience above ground. Soil moisture tells you whether roots and seeds have enough water. Daylight tells you where you are in the season and how much growing time remains.

Together, the four numbers turn a calendar-based garden plan into a conditions-based garden plan.

Instead of asking only, “What month is it?”

Ask:

“What are the numbers telling me that I can plant now?”

1. Soil Temperature: The Primary Planting Signal

Soil temperature is the starting point for deciding what to plant.

Seeds germinate in the soil, and newly transplanted plants establish their roots in the soil. A calendar may tell you that it is spring or fall, but soil temperature tells you whether the ground is actually ready for a particular crop.

That is why The Garden Soil Report puts soil temperature first.

For vegetables, I pay particular attention to the temperature of the soil at about 4 inches deep. The deeper soil temperature changes more slowly than the air temperature and provides a better indication of the conditions surrounding developing roots.

Cool-season vegetables

Cool-season vegetables can tolerate and often prefer cooler soil.

Think:

Lettuce
Spinach
Peas
Radishes
Carrots
Beets
Broccoli
Cabbage
Kale
Chard
Turnips
Cilantro
Parsley

As a practical guide:

Below 40°F: Germination of many crops will be slow or unreliable.
40–50°F: Many hardy cool-season crops can be planted, although germination may be slow.
50–60°F: A good planting range for many cool-season vegetables.
60–70°F: Still suitable for many fall crops, although some cool-season seeds prefer cooler soil.
Above 70°F: Some cool-season crops become increasingly difficult to establish from seed.
Above 80°F: Many cool-season seeds may germinate poorly or unevenly.

This is especially important in fall. September may be the calendar month for planting lettuce and spinach, but if the soil is still 78°F, the garden may not yet be ready for them.

Warm-season vegetables

Warm-season vegetables need warmer soil.

Think:

Tomatoes
Peppers
Eggplant
Cucumbers
Squash
Melons
Beans
Corn
Okra
Sweet potatoes

As a practical guide:

Below 50°F: Too cold for most warm-season vegetables.
50–60°F: Still marginal for many warm-season crops.
60–65°F: The beginning of the planting window for many warm-season crops.
65–75°F: A strong planting range for many warm-season vegetables.
75–85°F: Excellent conditions for many heat-loving crops, provided moisture is adequate.
Above 85°F: Heat can become a factor, especially in shallow or rapidly drying soil.

For tomatoes, peppers, and eggplant, I would not rely on one warm reading. I want to see the soil temperature consistently warm enough for the crop.

The transition zone

One of the most useful things about soil temperature is that it reveals the transition between seasons.

When soil temperatures are:

Rising through the 50s and 60s in spring: The garden is moving toward warm-season planting.
In the 60s and 70s in late summer: Warm-season crops remain comfortable.
Falling through the 70s and 60s in fall: The garden is moving toward cool-season planting.
In the 50s and 40s in late fall: Hardy cool-season crops increasingly take over.

The calendar says what season it is.

Soil temperature tells you what season the soil is actually experiencing.

2. Air Temperature: Does the Weather Agree?

Once soil temperature tells you that the ground may be ready, look at the air temperature.

There are two numbers to watch: the daytime high and the overnight low.

Daytime highs

Warm-season vegetables generally benefit from warm days.

Below 60°F: Warm-season crops may grow very slowly.
60–70°F: Warm-season crops can begin growing, although conditions may still be marginal.
70–85°F: Many warm-season vegetables grow actively.
85–95°F: Heat-loving crops can grow vigorously if moisture is adequate.
Above 95°F: Heat stress becomes increasingly important for many crops.

Cool-season vegetables generally prefer the other end of the range.

As temperatures rise, lettuce and spinach may bolt, radishes may become less desirable, and many brassicas may struggle.

Overnight lows

The overnight low can be just as important as the daytime high.

A garden with an 80°F afternoon and a 45°F night is very different from a garden with an 80°F afternoon and a 60°F night.

Below 50°F: Many warm-season crops slow down.
50–60°F: Warm-season crops can grow, but some remain sensitive to cool nights.
Consistently above 60°F: Conditions become increasingly favorable for vigorous warm-season growth.

So when soil temperature says “plant”, air temperature helps answer the next question:

“Will the plant be comfortable after I put it in the ground?”

3. Soil Moisture: Is the Soil Ready to Support the Plant?

Temperature tells you whether the soil is warm or cool.

VWC tells you how much water is available in it.

VWC—volumetric water content—is expressed as a percentage and gives us a way to monitor soil moisture over time.

As a practical working guide:

Below 20% VWC: Soil is becoming dry for many garden situations.
20–25%: Moisture is becoming more available, but some crops may still need attention.
25–35%: A useful target range for many garden soils.
Above 35%: Soil is quite moist; irrigation may not be necessary, depending on soil type and drainage.
Very high readings: Saturated soil can deprive roots of oxygen even though water is abundant.

These are working ranges rather than universal rules. Soil texture, bed construction, crop, root depth, and sensor placement all affect what a particular VWC reading means.

Temperature and moisture belong together.

A soil temperature of 72°F with VWC at 30% presents a very different planting environment from 72°F with VWC at 8%.

Warm soil + adequate moisture: Good conditions for active root growth.
Warm soil + dry soil: Seeds may fail to germinate and transplants may struggle.
Cool soil + adequate moisture: Plants may remain healthy but grow slowly.
Cool soil + saturated soil: Roots may have difficulty getting enough oxygen.

This is why the Garden Soil Report gives you both numbers.

Temperature tells you whether the soil is ready. Moisture tells you whether the soil can support what you plant.

4. Daylight: How Much Season Is Left?

Daylight is the fourth number, and it becomes especially important as the seasons change.

In spring, daylight increases.

In fall, daylight decreases.

The change may be only a few minutes from one week to the next, but plants respond to it.

Increasing daylight

Longer days generally mean:

More hours of photosynthesis
Increasing growth
Increasing water use
More energy available for plant development

But longer days do not override cold soil.

A garden can have long spring days while the soil is still too cold for warm-season crops.

That is why soil temperature comes first.

Decreasing daylight

In fall, the opposite happens.

As daylight shortens:

Growth gradually slows.
Soil begins losing its summer warmth.
Warm-season crops have less time each day to photosynthesize.
Ripening can slow.
Cool-season crops become increasingly comfortable.
The remaining growing season becomes more important.

This is why fall planting requires more than knowing the soil temperature.

A soil temperature of 68°F might still be excellent for planting a particular crop, but if the days are rapidly shortening and the crop requires 70 days to mature, you also need to ask whether there is enough season remaining.

5. The Four Numbers Working Together

The four numbers have different jobs.

Soil temperature asks:

Is the soil ready for this crop?

Air temperature asks:

Will the plant be comfortable above ground?

Soil moisture asks:

Is there enough water available for germination and root growth?

Daylight asks:

How much growing time and light remain?

The planting decision comes from considering all four.

For warm-season crops

Start with soil temperature.

Then look at:

Overnight lows
Daytime highs
Soil moisture
Remaining daylight
Days to maturity
First fall frost, when planting late in the season

A warm soil temperature may open the planting window, but cold nights or extreme heat can modify the decision.

For cool-season crops

Again, start with soil temperature.

Then look at:

Daytime temperatures
Overnight temperatures
Soil moisture
Shortening daylight
Days to maturity
Expected frost or winter conditions

The goal is often to plant while the soil is still warm enough for quick establishment but the air is becoming cool enough for the crop to thrive.

6. Spring: Using the Numbers to Know When to Plant

Spring is the season when gardeners are most tempted to plant according to the calendar.

But spring weather can be deceptive.

A warm week can arrive while the soil remains cold.

So begin with the soil.

When soil temperatures are in the 40s and 50s

Think cool-season vegetables.

This is the time for crops such as:

Peas
Lettuce
Spinach
Radishes
Carrots
Beets
Brassicas

As soil temperatures rise, the list of crops you can plant expands.

When soil temperatures reach the 60s

The warm-season garden begins to open.

Depending on air temperatures and the individual crop, this can be the beginning of the planting window for:

Beans
Corn
Cucumbers
Squash
Melons
Tomatoes
Peppers
Eggplant

But don’t stop at soil temperature.

Check the overnight lows.

A warm soil with cold nights may mean that some warm-season transplants should wait.

7. Fall: Using the Numbers to Know When to Change Crops

Fall requires a different kind of attention.

The question is not simply:

“What can I plant?”

It is also:

“How much growing season do I have left?”

Start with soil temperature.

As the soil cools from summer temperatures:

Warm-season crops gradually become less productive.
Cool-season crops become increasingly appropriate.
Germination conditions improve for many fall crops.

Then add daylight.

Shortening days mean that plants will have progressively less energy available each day.

Finally, consider:

Days to maturity
First expected frost
Crop hardiness

A crop that needs 30 days to mature is a very different proposition from one that needs 80 days.

In fall, soil temperature tells you what you can plant; daylight and the remaining growing season tell you what is still practical to plant.

8. What the Numbers Mean for Harvesting

The same numbers that guide planting also help explain what is happening to crops already in the garden.

Warm-season crops

When soil and air temperatures are warm:

Tomatoes ripen more quickly within their preferred temperature range.
Cucumbers, squash, and beans can produce rapidly.
Water use increases.
Very high temperatures can interfere with flowering and fruit set.

As temperatures and daylight decline:

Growth slows.
Ripening can take longer.
Production gradually decreases.

Cool-season crops

As temperatures moderate:

Lettuce becomes less prone to bolting.
Spinach becomes more comfortable.
Brassicas grow more readily.
Many root crops continue developing in cool soil.

Fall can therefore shift the garden from fast summer production to slower, more durable cool-season growth.

9. What the Numbers Mean for Annual Flowers

Vegetable crops are not the only plants affected by these conditions.

Annual flowers respond to soil temperature, air temperature, moisture, and daylight as well.

Warm-season annuals

Zinnias, marigolds, sunflowers, cosmos, and many other warm-season annuals generally prefer:

Warm soil
Warm air
Adequate moisture
Plenty of sunlight

Cold soil can delay germination and establishment.

As fall approaches, shortening days and cooling temperatures gradually reduce growth and flowering.

Cool-season annuals

Pansies, violas, calendula, snapdragons, sweet peas, and other cool-season annuals become increasingly appropriate as summer heat declines.

For fall planting, the objective is often to establish them while soil temperatures remain favorable and before colder conditions arrive.

10. What the Numbers Mean for Perennials

Perennials require a somewhat different interpretation.

You are not usually trying to produce a harvest within a few weeks. You are trying to establish a plant that will remain in the garden for years.

For that reason, root establishment becomes especially important.

When planting perennials

Look for:

Moderate air temperatures
Suitable soil temperature
Adequate soil moisture
Soil that is workable rather than saturated
Enough time for roots to establish before severe heat or cold

Fall can be an excellent establishment season in many climates because soil may remain relatively warm while air temperatures become more moderate.

The plant may not produce much new top growth, but its roots can continue developing.

For a perennial, planting is an investment in next season and the seasons after that.

11. What the Numbers Mean for Shrubs and Trees

Trees and shrubs respond more slowly than vegetables, but the same principles apply.

Soil temperature

Warm enough soil supports root activity and establishment.

Air temperature

Extreme heat increases water loss and transplant stress.

Soil moisture

Newly planted trees and shrubs need reliable moisture while their root systems are becoming established.

Daylight

Shortening days help signal the seasonal transition for many deciduous trees and shrubs.

For woody plants, the most useful question is often not:

“Will I see new growth this week?”

but:

“Are conditions favorable for this plant to establish a healthy root system before the next period of heat, cold, or drought?”

12. When the Numbers Say “Wait”

One of the most useful things a gardener can learn from the Garden Soil Report is that not planting can be the right decision.

Wait on warm-season crops when:

Soil temperature is too low.
Overnight temperatures remain too cold.
Soil moisture is inadequate.
Extreme heat is arriving immediately after planting.
There is not enough growing season remaining for the crop to mature.

Wait on cool-season crops when:

Soil temperature is still excessively warm.
Air temperatures remain too hot.
Newly planted seed would dry out before germinating.

The garden does not always say “plant now.”

Sometimes the numbers say:

Wait.

And waiting for the right conditions can produce a better crop than planting on the right calendar date.

13. The Soil-Temperature Principle

The central idea behind The Garden Soil Report is simple:

Plant according to the conditions in the soil, not simply according to the calendar.

Soil temperature is the starting point.

Then use the other numbers to interpret what that temperature means.

Soil temperature: What can I plant?
Air temperature: Will the plant be comfortable?
Soil moisture: Can the seed or plant establish?
Daylight: How much season remains?

For late-season planting, add:

Days to maturity: How long does the crop need?
First frost date: How much time is actually available?

The numbers do not replace a gardener’s judgment.

They give the gardener better information on which to base it.

14. The Garden Soil Report in One Sentence

When you open the weekly report, start here:

Soil temperature tells you what the ground is ready for; air temperature, soil moisture, and daylight tell you whether the conditions will support it.

That is what the numbers mean.

And once you begin reading them this way, the garden becomes less dependent on a planting calendar and more responsive to the conditions actually under your feet.