Tomatoes and potatoes are not good companion plants and should be kept apart

No—tomatoes and potatoes should not be planted near each other, even though they are both nightshades and seem like they would work well together. They share the same pests and diseases, which means planting them close together creates ideal conditions for problems to spread quickly from one plant to the other. The most serious shared threat is late blight, a fungal disease that can wipe out both crops in the same season.

The reason gardeners sometimes consider pairing them is that both grow well in similar soil and sunlight conditions. But those similarities are exactly why they are poor companions—what helps one also helps the diseases and insects that attack both. Spacing them far apart in your garden, or in different garden beds entirely, is the simplest way to protect your harvest.

Key Takeaways

  • Tomatoes and potatoes share the same major pests and diseases, especially late blight fungus, which spreads rapidly between nearby plants.
  • Late blight can destroy both crops in a single season if plants are grown close together, particularly in cool, wet weather.
  • Keeping tomatoes and potatoes at least 10 to 15 feet apart, or in separate garden areas, significantly reduces disease pressure on both plants.
  • Good tomato companions include basil, carrots, and marigolds, while potatoes grow well with beans, corn, and garlic.

Why late blight spreads between tomatoes and potatoes

Late blight is a fungal disease caused by Phytophthora infestans that attacks both tomato foliage and potato tubers. The fungus spreads through water—rain splash, overhead watering, or even morning dew on leaves—and can travel from one plant to another in hours during cool, wet conditions. Once it takes hold, it can destroy a mature tomato plant in three to five days and render potatoes inedible or unmarketable.

The disease starts as water-soaked spots on leaves, usually on the lower foliage first. On tomatoes, the spots spread upward and can eventually kill the entire plant. On potatoes, the fungus moves down into the soil and infects the tubers, causing rot that makes them unsuitable to eat or store. If you have late blight on one plant and the other is nearby, the spores will almost certainly reach it within days.

The risk is highest in regions with cool summers and frequent rain, but late blight can occur anywhere during wet springs or falls. Even a single infected plant left in the garden over winter can be a source of infection the following year.

Other pests and diseases that affect both crops

Beyond late blight, tomatoes and potatoes attract the same major insect pests. Colorado potato beetles eat the foliage of both plants, and their larvae can defoliate a young plant in days. Hornworms and whiteflies also attack both crops. If you plant them close together, you create a buffet that makes it easier for these pests to move between plants and build up large populations.

Early blight, another fungal disease, also affects both tomatoes and potatoes. It causes brown, concentric rings on lower leaves and can eventually girdle the stem. Like late blight, it spreads through water and soil contact, so proximity increases the risk of infection moving from one plant to the other.

Verticillium wilt, a soil-borne fungus, can also infect both plants. Once the fungus is in your soil, it persists for years, so planting tomatoes and potatoes in the same bed year after year increases the likelihood of buildup and crop loss.

How far apart to plant tomatoes and potatoes

A safe distance between tomato and potato plants is at least 10 to 15 feet. This spacing reduces the chance that fungal spores or insect pests will move between the two crops. In a small garden where that distance is not practical, planting them in separate beds or on opposite sides of the garden is the next best option.

If you use the same soil or compost for both crops, make sure to clean your tools between working in each area. Fungal spores and soil-borne pathogens can travel on unwashed shovels, hoes, and hands. Washing your hands and tools with soap and water after handling potatoes and before touching tomatoes reduces cross-contamination.

Rotating crops year to year also helps. Do not plant tomatoes where potatoes grew the previous season, or vice versa, for at least two to three years. This breaks the cycle of soil-borne diseases and reduces pest populations that overwinter in the soil.

Better companion plants for tomatoes

Basil is one of the best tomato companions. It repels some insect pests and is said to improve tomato flavor, though the main benefit is that it does not share tomato diseases. Plant basil at the base of tomato plants or nearby in the same bed.

Carrots and onions grow well alongside tomatoes without competing for nutrients or attracting the same pests. Marigolds are often planted near tomatoes because they may deter some insects, though their main advantage is that they do not harbor tomato diseases. Parsley, borage, and nasturtiums are also safe choices that can fill space without creating pest or disease problems.

Avoid planting tomatoes near brassicas (cabbage, broccoli, kale) or fennel, as these can inhibit tomato growth or attract overlapping pests. Corn and potatoes should also be kept away from tomatoes for the reasons outlined above.

Better companion plants for potatoes

Beans are excellent potato companions. They fix nitrogen in the soil, which potatoes benefit from, and they do not share potato pests or diseases. Corn and peas also work well with potatoes for the same reason. Garlic and onions may help repel some potato pests and do not create disease pressure.

Marigolds planted around potatoes may reduce pest pressure, and nasturtiums can act as a trap crop, attracting aphids away from the potatoes. Horseradish is sometimes planted at the edges of potato beds as a pest deterrent.

Keep potatoes away from tomatoes, peppers, eggplants, and other nightshades. Brassicas like cabbage can also inhibit potato growth, so space them apart. Fennel should not be planted near potatoes, as it can stunt their growth.

Signs that disease is spreading between your plants

If you have already planted tomatoes and potatoes close together, watch for the early signs of late blight or early blight. On tomatoes, look for water-soaked spots on lower leaves that spread upward, or brown rings with concentric patterns. On potatoes, check for similar spots on foliage and dig a sample plant to see if the tubers show soft rot or dark discoloration.

If you spot these signs, remove the affected plant when ready and dispose of it in the trash—do not compost it, as the fungus can survive in compost. Increase spacing between remaining plants if possible, avoid overhead watering, and water only at the base of plants in the early morning so foliage dries quickly. These steps can slow disease spread, but once late blight is established, it is difficult to stop without fungicide.

If disease appears on one crop, inspect the other crop closely every few days. Early detection and removal of infected leaves can sometimes prevent total crop loss, though prevention through spacing is far more effective than treatment after infection occurs.

Frequently Asked Questions

Can I plant tomatoes and potatoes in the same garden bed if I space them far apart?

Spacing helps, but the safest approach is to use separate beds entirely. Even 10 to 15 feet apart in the same bed, fungal spores can still travel through water splash or soil contact. If you must use the same bed, keep them as far apart as possible and avoid overhead watering.

What if I already planted tomatoes and potatoes together?

Monitor both plants closely for signs of disease, especially during cool, wet weather. Water only at the base of plants, remove any diseased leaves when ready, and increase air circulation by pruning lower foliage. If late blight appears, remove the affected plant and consider moving the other crop to a different location next season.

Can I use the same soil for tomatoes one year and potatoes the next?

It is better to wait two to three years between planting tomatoes and potatoes in the same soil. Soil-borne diseases like verticillium wilt and early blight can persist in the soil and infect the next crop. Rotating to unrelated plants in between reduces disease buildup.

Do I need to use fungicide if I plant tomatoes and potatoes close together?

Fungicide can help manage disease, but it is not a substitute for spacing. Prevention through distance and good cultural practices—like avoiding overhead watering and removing infected leaves—is more reliable and less costly than relying on fungicide alone.

What is the difference between early blight and late blight?

Early blight causes brown rings with concentric patterns on lower leaves and appears in warm weather. Late blight causes water-soaked spots and appears in cool, wet conditions and is far more destructive. Both affect tomatoes and potatoes, but late blight spreads faster and is harder to control.