What this companion planting checker does
The checker compares two plants using practical concerns that affect a shared bed: growing season, mature size, light, water, root room, and airflow. It returns a practical match, a caution, or no clear conflict.
A practical match does not mean the plants improve each other. It means they can reasonably share space when their individual spacing requirements are respected. A caution does not mean the pair is toxic or impossible. It identifies a likely conflict that needs a different season, more room, or another layout.
What the result does not prove
Companion planting lists often promise pest control, improved flavor, or faster growth without explaining the conditions or evidence behind the claim. This checker does not treat those promises as guaranteed effects.
Anecdotes can be useful observations, but they do not establish that one plant caused an outcome. Weather, variety, soil, planting density, and pest pressure can all change at the same time. Use companion ideas as layout hypotheses, not substitutes for crop care and observation.
How to evaluate a plant pair
Compare the season
Plants that prefer different temperatures can be difficult to grow together at their best. A cool-season crop and a heat-loving crop may use the same bed successfully in succession rather than at the same time.
Compare mature size
Small transplants can become large plants. Estimate the final canopy and root area before filling empty soil around a young crop. One plant should not block the light or airflow needed by the other.
Compare water needs
Plants sharing one irrigation zone should tolerate a similar watering pattern. A pair can look compatible on a list and still struggle if one needs consistently moist soil while the other performs poorly under the same treatment.
Protect airflow
Crowding creates long periods of leaf wetness and makes inspection difficult. Even a practical pair needs its normal spacing. Companion planting is not a reason to ignore mature dimensions.
Understanding the three results
Practical match
The pair can share broadly similar conditions or use the space at different stages. Read the explanation for the limitation. Lettuce beneath young tomatoes, for example, becomes less practical as the tomato canopy expands.
Plan with care
The plants have a likely conflict in season, mature footprint, or resource use. They may still fit in a large bed or a carefully timed succession, but they should not be crowded by default.
No clear conflict
The checker has no strong practical warning recorded for the pair. This is not a claim of benefit. Compare the plant labels and your own conditions before deciding on the layout.
Worked examples
Tomato and basil
Both prefer warm, sunny conditions and regular watering. Basil can occupy nearby space, but it still needs light and the tomato needs airflow. The pair works because their care can overlap, not because pest protection is guaranteed.
Tomato and lettuce
Lettuce can use open soil while a tomato is still small. As the season warms and the tomato expands, shade and root competition increase. This pairing is often most useful as a timed sequence.
Tomato and cucumber
Both become large summer crops. In a small bed they can compete for sun, root room, support space, and airflow. A bigger layout or separate beds can be easier to manage.
Broccoli and pepper
Broccoli generally performs in cooler periods, while peppers need sustained warmth. Using the same bed in succession may suit both better than forcing them into one planting window.
Make a useful bed plan
Start with the largest or longest-lived crop. Give it the space, support, and sun position it needs at maturity. Fit shorter or quicker crops only where they will not prevent access or become trapped beneath a canopy.
Then check irrigation and planting dates. Plants that share water needs but not seasons may still be good users of the same bed at different times. Record what happens so next season's layout reflects your garden rather than a generic chart.
Common companion planting mistakes
Treating compatibility as permission to crowd
Two compatible plants still need room. Use the plant spacing calculator after checking a pair.
Expecting one plant to solve pest problems
Use routine inspection, crop health, physical barriers, and locally appropriate pest management. Do not rely on a neighboring plant as guaranteed protection.
Ignoring the direction of shade
Tall crops and trellises can cast shade beyond their own spacing circle. Place them where they will not block sun from shorter crops that need it.
Repeating the same plant family in one spot
A companion layout does not replace crop rotation. Related crops can share disease and pest pressures even when their care requirements are similar.
When this checker is not enough
The tool compares only two plants and uses generalized growing characteristics. A mixed bed with several crops needs a full layout, planting schedule, and rotation plan. Cultivar size and local conditions should take priority over a generic pair result.