Planting Tomatoes and Potatoes Together Is Not Recommended

You can physically plant tomatoes and potatoes in the same garden bed, but gardeners and extension services generally advise against it. Both plants are susceptible to the same diseases—particularly late blight and early blight—and they compete for the same nutrients in the soil. When one plant gets sick, the other usually follows within days or weeks. The risk of losing both crops outweighs any space savings you might gain.

The main problem is disease transmission. Tomatoes and potatoes are both members of the nightshade family (Solanaceae), which means they share the same pests and pathogens. Late blight, a fungal disease that destroyed potato crops historically, spreads rapidly between the two plants. If your potatoes develop the disease, your tomatoes are already at risk by the time you notice the first spots.

Key Takeaways

  • Tomatoes and potatoes are both nightshade plants and catch the same diseases, particularly late blight and early blight, which spread quickly between them.
  • Both plants draw heavily on nitrogen and potassium, so planting them together depletes soil nutrients faster than either would alone.
  • Spacing tomatoes and potatoes at least 3 to 4 feet apart, or in separate garden beds, reduces disease spread and improves yields for both crops.
  • If space is limited, grow potatoes in spring and tomatoes in summer in the same bed, waiting at least 4 weeks between harvests to break the disease cycle.

Why Disease Spreads Between These Two Plants

Late blight fungus survives in soil and on plant debris. When you water tomatoes and potatoes planted side by side, water splashes from one plant to the other, carrying spores. The fungus also spreads through the air on humid days. Once it takes hold in potatoes—which are more vulnerable early in the season—it moves to nearby tomatoes within 7 to 14 days.

Early blight, another common fungal disease, works the same way. It starts on lower leaves and climbs upward, and it affects both crops equally. If you have had either disease in your garden before, planting these two crops together nearly guarantees it will return. Removing infected leaves slows the problem but does not stop it once both plants are infected.

Nutrient Competition and Soil Depletion

Tomatoes and potatoes both demand large amounts of nitrogen early in the season and potassium throughout growth. When planted together, they compete for the same nutrients, and neither plant gets what it needs. The result is smaller potatoes, fewer tomatoes, and weaker plants overall.

Potatoes are especially heavy feeders. They pull nitrogen from the soil rapidly, which leaves less available for tomatoes. If you have already amended your bed with compost or fertilizer, planting both crops together means you are dividing those nutrients between two hungry plants instead of giving each one its own supply. Soil testing before planting shows whether your bed has enough nutrients for either crop alone—it almost certainly does not have enough for both.

The Best Spacing If You Plant Them Nearby

If your garden is small and you must plant tomatoes and potatoes in the same area, space them at least 3 to 4 feet apart. This distance does not eliminate disease risk, but it slows transmission. Air circulation improves, and water splashing is less likely to reach from one plant to the other.

Even with good spacing, monitor both crops closely. Check the undersides of leaves weekly for spots or discoloration. Remove any affected leaves when ready and dispose of them in the trash, not the compost pile. Water at the soil level only, never overhead, to avoid splashing spores between plants. These steps reduce risk but do not remove it entirely.

Succession Planting: Growing Them in the Same Bed at Different Times

A safer approach is to grow potatoes in spring and tomatoes in summer in the same bed. Plant potatoes in early spring, harvest them by early summer, and then plant tomatoes in the same space 4 to 6 weeks later. This timing allows soil-borne disease spores to break down and reduces the chance that pathogens from potatoes will still be active when tomatoes go in.

Before planting tomatoes, remove all potato debris—stems, leaves, and any small tubers left in the soil. Add fresh compost to replenish nitrogen that potatoes depleted. This method uses your space efficiently and keeps both crops healthy. It does require patience and planning, since you cannot harvest potatoes and plant tomatoes on the same day.

Better Companion Plants for Each Crop

Tomatoes grow well alongside basil, carrots, marigolds, and parsley. These plants do not compete for the same nutrients and do not carry the same diseases. Basil in particular is said to improve tomato flavor, though the main benefit is that it takes up little space and does not stress the soil.

Potatoes pair better with beans, corn, and onions. Beans actually add nitrogen to the soil as they grow, which helps potatoes. Corn provides a natural trellis for beans in a three-sisters arrangement. Onions repel some potato pests and do not compete for nutrients. Choosing these companions instead of tomatoes gives you more harvest from the same bed.

What to Do If You Already Have Both Planted Together

If tomatoes and potatoes are already growing side by side in your garden, do not pull them out. Instead, increase your monitoring and adjust your care. Water only at soil level, never overhead. Remove lower leaves from both plants as they age to improve air circulation. Thin the plants so light reaches the center of each one.

Watch for the first signs of disease: brown or black spots on leaves, yellowing that starts at the bottom, or a white mold on leaf undersides. At the first sign, remove affected leaves and spray with a fungicide labeled for both tomatoes and potatoes—sulfur or copper-based products work on both crops. Do this every 7 to 10 days during humid weather. Harvest potatoes as soon as they are ready rather than waiting, so you can remove that crop and reduce disease pressure on tomatoes.

Frequently Asked Questions

Will planting tomatoes and potatoes together definitely ruin both crops?

Not always, but the risk is high. In a dry year with good air circulation, you might avoid disease. In a wet or humid year, disease spreads quickly and can destroy both crops. It is not worth gambling with your harvest when spacing them apart takes little extra effort.

Can I plant potatoes where tomatoes grew last year?

Wait at least one year before planting potatoes in soil where tomatoes grew. Disease spores can survive in soil for months. A full season of growing other crops allows spores to break down. If you had late blight the previous year, wait two years before planting potatoes in that spot.

What if I only have room for one crop—which should I choose?

Tomatoes typically produce more food per square foot than potatoes and grow well in containers. If space is truly limited, grow tomatoes and buy potatoes from the store. If you prefer homegrown potatoes, grow them in a dedicated bed or large container separate from any nightshade plants.

Does mulch help prevent disease spread between the two plants?

Mulch helps by preventing soil from splashing onto leaves, but it does not stop airborne spores. Use 2 to 3 inches of straw or wood chips around both plants, keeping it a few inches away from the stem. Mulch also keeps soil moisture steady, which reduces stress on both crops—less stressed plants resist disease better.

Can I use the same soil for potatoes one year and tomatoes the next without waiting?

You can, but disease risk remains high if spores are present. If you did not have disease problems the previous year, you can plant tomatoes in potato soil after removing all plant debris and adding fresh compost. If disease was present, wait a full year or use fresh soil brought in from elsewhere.