What to Plant Together Right Now in Southeast Massachusetts

The ground in Plymouth is finally workable. Not warm -- the soil is sitting around 38 to 42 degrees right now -- but workable. If you can get a fork in without hitting frozen chunks, the cool-season window is open. And for those of us between Boston and the Cape, that window is one of the most productive stretches of the growing year if you use it right.

This is not tomato and pepper season. That conversation starts in late May at the earliest around here, and even then I like to wait until the soil hits 60 degrees before transplanting anything in the nightshade family. Right now the stars of the show are peas, spinach, lettuce, radishes, carrots, and brassica transplants. And the companion pairings you set up this month will pay off for the next three months.

Peas are the first thing I get in the ground every year, usually the last week of March or first week of April depending on how the winter went. Sugar Snap from Johnny's has been my go-to for years. Peas are cold-tolerant down to about 28 degrees once established, and they germinate in soil as cool as 40 degrees. The companion pairing that matters most here is peas with carrots. Peas fix nitrogen through their Rhizobium root nodules, and that nitrogen becomes available to the carrots growing alongside them. Both are cool-season crops that thrive in the same conditions. I sow carrot seed right alongside the pea row -- the peas come up fast and mark the row while the carrots take their time germinating over the next two to three weeks.

But here is the pairing to avoid with peas: do not plant them near your garlic. If you put garlic in last October like most of us on the South Shore, those cloves are already pushing green shoots. Garlic root exudates contain organosulfur compounds that suppress the Rhizobium bacteria peas need for nitrogen fixation. A 1996 study in Plant and Soil documented a 20 to 40 percent reduction in nitrogen fixation when legumes were grown near alliums. Keep your pea rows on the opposite side of the bed from the garlic.

Spinach is another crop that should be going in right now. Sun Angel from Johnny's has been my best performer -- it handles the cold well and is slow to bolt when things warm up in May. For companion planting, spinach does well next to strawberry beds. If you have established strawberry rows, sow spinach between them while the strawberry canopy is still low in early spring. The spinach fills the empty space, suppresses early weeds, and gets harvested before the strawberries need the room. Both crops prefer the same cool, moist conditions we have right now.

Radishes are the fastest return in the spring garden. Rover and Sora from Johnny's both mature in about 25 days. The best companion use for radishes right now is as row markers and soil breakers for slow-germinating crops. Sow radish seed mixed with carrot seed or parsnip seed. The radishes germinate in four to five days, marking your rows so you know where you planted. Their taproots break the surface crust, making it easier for the delicate carrot seedlings to push through. By the time the carrots need the space, you have already harvested the radishes.

For lettuce, this is the ideal planting window. Buttercrunch is reliable and handles our spring temperature swings well. The companion pairing I rely on is lettuce with chives. If you have an established chive clump -- and most South Shore gardeners do, they are practically unkillable -- divide it and plant divisions along the edges of your lettuce bed. Chive volatiles deter the aphids that love lettuce, and when the chives flower in May, those purple blooms attract hover flies and parasitoid wasps that provide biological pest control for the rest of the season.

Brassica transplants are the other big move this month. If you started broccoli, cabbage, or cauliflower indoors six to eight weeks ago, they are ready to go outside now with some row cover protection on the coldest nights. The companion pairing with the strongest research behind it is brassicas with sweet alyssum. Undersow alyssum seed at the same time you transplant your brassicas. The alyssum establishes as a living mulch beneath the broccoli or cabbage, and when it blooms it attracts hover flies whose larvae eat cabbage aphids. Eric Brennan's research at USDA showed 50 to 70 percent aphid reductions with this one pairing. That is significant pest suppression from a flower that costs a couple dollars for a packet of seed.

One more pairing for March: onions and carrots. If you are putting in onion sets or transplants this month -- and you should be, the South Shore has ideal onion planting conditions from mid-March through mid-April -- plant them in alternating rows with your carrots. The onion volatiles mask the carrot scent from carrot fly, and research by Uvah and Coaker showed 50 to 75 percent reductions in carrot fly egg-laying when onions were interplanted. This is one of the most well-documented companion pairings in the scientific literature, and it is perfectly timed for our spring planting season.

What about garlic? Your fall-planted garlic is already up and growing. It is a fantastic companion for strawberries -- the allyl sulfide compounds deter spider mites and show antifungal activity against gray mold and anthracnose, two diseases that hit strawberries hard in our humid coastal climate. If your garlic rows are not already near your strawberry beds, make a note for next October's planting.

The common thread in all of these pairings is that they are working through real mechanisms -- volatile chemistry masking pest signals, nitrogen fixation feeding neighboring crops, beneficial insect recruitment through flowering companions. None of it requires any sprays or products. Just thoughtful placement of plants that have documented interactions.

You can look up the full research behind any of these pairings in our companion planting guide, or check exact planting dates for your zone in the growing guide. If you want companion planting, succession scheduling, and biodiversity built into a complete plan for your yard, that is what we do -- schedule a consultation and we will walk your property together.