What to Start Seeding and Planting in May

May is moving day for young seedlings. I am constantly moving trays of flowers and vegetables from the growing room to my popup greenhouse for more space, or hardening them off outside to get ready to go into the ground. As they move out, they make room to seed-start the next group of flowers and vegetables for the mid summer. If you catch me outside, there’s a good chance there are a few seed packs in my pocket to remind me to put something in the ground, too. Summer is just starting, but there are lots of seeds to be planted right now, either inside to grow into starts, or direct seeding outside.

Lawns

Take advantage of the last of the rains to help germinate lawn seed. If your lawn has patches that need some reseeding or you want to plant a whole summer lawn, work with your local garden center to find the right seed. Germination is really dependent on water, so you want to balance last frost date and warm enough weather for the seed you plant with there being enough rain so you’re not watering constantly. 

It’s not just traditional lawns, either. If you’ve got an eco lawn or clover lawn, you can flesh out the area by adding red and strawberry clover seed for the summer as well as English daisy seed. Ideally, you’re not creating a monoculture of one kind of seed, so other low lying flowers can be added in. 

Annual flowers

In most parts of the U.S., you’ll start to get enough sunshine this month to direct seed outside, which just means you’ll plant the seeds in the soil, rather than try to grow seedlings inside to plant outside later. If you’re going to try to direct-seed annuals like wildflowers, they can start going in the ground as soon as you’ve reasonably passed the risk of frost. Pay attention to the packet for instructions as to depth of seeds—many seeds can not germinate by simply being sprinkled on top of the soil; they need cover of soil. Your sunflower seeds, for instance, need a depth of an inch or so. A good basic rule is that seeds need to be planted as deep as their size. So tiny seeds like celosia and poppy are ok to be sowed on the surface, but marigolds and zinnia must be planted about half an inch deep. If you want to scatter the seeds to get a more natural look rather than poke holes for the seeds, scratch up an area so there’s soil contact for the seeds, then scatter them and cover them by sprinkling soil on top and patting it down. Finish by watering. 

Remember that summer is finite, so if you haven’t planted annual flower starts and you want to direct seed, you’ll want to do so before the end of May—although you may succession-seed another round of flowers later this summer, like zinnias or sunflowers. 

Vegetables

All of your tender summer vegetables benefit from going into your garden as seedlings, rather than seeds. The summer is just so short that that you want to ensure you have enough runway to grow tomatoes and eggplants and peppers before it’s over. Generally, most people either grow or buy starts for the rest of their garden as well, including pumpkins, corn, cucumbers, squash, and beans. But you can direct-seed these, and now is the time to do so. Direct-seeding has some upsides: You don’t need room inside to grow them or soil and pots. The downside is that seeds outside are a little more vulnerable to squirrels and birds, and those young shoots are vulnerable to snails, slugs, and squirrels. All this to say: You should over-plant (and remember to follow the seeding instructions on the seed package for the appropriate depth of different types of seeds). 

Be sure that you take advantage of the last spring rain to germinate additional rounds of carrots. Since they need constant moisture during germination, the rain can carry the load here. This time of year, I leave the radish, lettuce, green onion, beet, and kohlrabi seeds outside in a protected spot so I’ll remember to seed them once a week. You don’t need to put out a packet’s worth each week, just the number that you’ll eat. It helps to mark rows as you go so you don’t plant in a spot you’ve already seeded. 

My favorite tip for having a summers’ worth of lettuce is to direct seed a long, low trough planter of lettuce, but you can just pick a corner of a planting bed. Dump the whole packet of seeds in and be sure to mix it with the top layer of soil so it’s distributed evenly. Water the packet and as it germinates, you'll have a planter packed with lettuce. But if it's too packed, it won’t grow much, so each week, I grab a scoop from the end of the planter, separate those seedlings, and plant them out in the garden beds. The planter acts as a holding space for lettuce most of the summer, and each week I pluck out a few to plant. 

Succession planting

Back inside, it’s time to get your mid-summer starts planted. This can be more lettuce if you prefer to grow it inside, but also chard, brassicas, beans, cucumbers, and mid-summer flowers. Again, you can direct seed these or grow them inside, which is a far more controlled environment.