"Can I put it outside yet?"
Different plants have different tolerances. Some types of plants thrive in cooler weather and some really don't like it. Planting your peas outside right now will get you a better crop than keeping them somewhere warmer, while sticking a tomato plant outside too early may in fact stunt it. It may look like it's surviving now, but it's more likely to struggle later on than a tomato that stayed indoors until the outside temps were at least 45° F. So sometimes trying to get a head start by putting things in the ground can actually delay your harvest. It really depends on the plant's individual needs.
It's also important to remember that a plant's age can affect its hardiness. Adult plants are more cold-hardy than seedlings, for example. The relative temperature of the season overall can also have an impact. Hotter summers can make some plants more susceptible to cold than a relatively cool summer.
I find it helpful to group plants with similar frost tolerances together, so I know who can go out first, who can go out next, and who goes last.
Look around outside and in your garden to see what plants are starting to come out of dormancy, and use that information to help you decide what can go outside now. If your poppies are starting to come up, you can harden off any poppies you have and plant them outside too. The hollyhocks haven't come up outside yet, so I'd hold off on putting any in the ground right now.
Watch the nighttime temperatures. I cannot stress this enough. We have wild temperature swings. It can be 70° F during the day, and then drop down to 30° at night. This fluctuation can be stressful for plants, and the nice daytime weather can trick us into thinking it's plenty warm enough to start a garden. The good thing about our wild nighttime swings is that the most drastic lows happen in such a short period of time just before dawn. There's a lot you can do to keep your soil temperature warmer and protect your plants for that short time.
- Have straw and frost cloth on hand. These are two of the best insulators for extra cold nights that could damage even the cold-hardy plants you have outside. Blankets, plastic bins, and even plastic sheets can work in a pinch, but keep in mind that plastic materials, especially, can collect condensation on the underside, which will freeze and harm any plants in contact with the material. Keep any plastic covering at least a few inches away from your plants if you need to use this method. Having hoops over your beds allows you to cover them with almost anything in a pinch. That said, if you stick with frost cloth, you can put it directly on top of your plants without harming them in a frost. Straw can be mulched heavily around and on top of plants as well if there's going to be super cold temps. Just pull back the straw from the plants. You can leave up to 1 inch of straw on top of the soil around your plants to help with soil retention year-round. Any plastic or blanket covering needs to be removed in the morning as the temperature rises, or you'll harm your plants. They'll get too hot in the mid-day sun. Frost cloth can be left on without much harm to plants.
- Water before a cold night. This may sound counterintuitive, but water can help maintain more consistent soil temperatures. Wet soil can retain heat, whereas dry soil can get much colder faster. If you water your garden in the afternoon or evening before cool nights, your soil temperature won't drop along with the air temperature. Just make sure to do this watering with plenty of daylight left, otherwise the leaves and tops of your plants may stay too soggy. I've had gardens with 4 basil plants in a row, and the only ones that survived were the two that got water before the cold nights. The other two stayed dry, and did not survive.
- Jugs of water on cold frames, or under covered hoops in garden beds can also help retain warmth. The jugs collect passive heat from the sun during the day, and then give off heat throughout the night. I've found black jugs and half-buried them in raised beds with covering to help keep things a couple degrees warmer. A large black rain catch barrel inside an unheated greenhouse uses this concept on a larger scale. You can use milk jugs on seedlings. Cut the bottom off a milk jug and stick it over small seedlings. Just be sure to take it off during the day, or your plants will fry in the heat.
- Rocks and raised beds.Ever notice all the little seedlings that tend to sprout up around rocks? Much like putting a jug of water around your plants to retain heat, placing rocks around plants to warm up during the day and release heat at night can help give your soil a temperature boost at night. Raised beds will also have a warmer soil temperature than those embedded right into the ground because the soil can be warmed by the sun on one side throughout the day.
What's in my garden
Crocuses are done. I have some daffodils that should be flowering any day now. Foxes have been eating at my tulip bulbs, but some of my tulips are starting to come up.
Evergreen bunching onion is up! These guys really don’t go all that dormant and stay nice and green even in the earliest part of spring. I bought some of these last year and the year before, and I just let them overwinter and turn into monsters each year. They will flower and drop seed but they are quite slow to spread, so I’m mostly leaving them in the ground until I have use for them, not because they’ll multiply. We should have these in stock by Mid-May in Greenhouse 5 at Petree's.
Chives are up and thriving. They pretty reliably come back year after year, and even two of my scrappy plants from last year came up looking better than ever. You can also divide your chives at this time into multiple plants if it’s getting too big. Chives are the most shade tolerant herb I know- taking a minimum of 4 hours of sun.
I have two beds of garlic - one hardneck and one soft - that are all up and looking lovely. I did have to pull back some of the heavy straw mulch I put on one of the beds to help the new sprouts poke through. I was worried, since one variety looked a little more dark green and healthy than the other, but as the temperatures warmed and I pulled off some of their bedding, their foliage has darkened in color and grown more sturdy looking.
Some of my fruit shrubs slowly coming out of dormancy. I have boysenberry, ‘Black Satin’ blackberry, a goji berry in a container, and a ‘Polana’ raspberry, all showing tiny buds, but not much else yet.
My Mexican hat plant, Rocky Mountain bee balm, catmint, yarrow, rudbeckia, and ‘Black Lace’ elderberry are all starting to come back underneath the straw covering I put on them.
I got brave and planted a couple strawberries. They seem to be doing well. They are okay outside in the pot, even down to 25º F, however it is important to note that the one that was planted lost all of the leaves it had when it was planted, but there is new growth/leaves growing up from the base. Sometimes the less hardened off or older leaves can be lost in the process of the plant putting more energy into roots. Don’t fret if you see old leaves die on a plant that is transitioning to a new environment. If there is still new growth from the base or the center of the plant, it should be fine.
Poppies have been outside for a few weeks now and are thriving.
I have some cilantro outside that is doing well. Cilantro is a cool-weather crop that bolts at consistently high temperatures. But when it bolts you get coriander seeds!
I planted onion starts outside last week since most of my other alliums are doing well.
I have leeks outside ready to go into the ground.
I have calendula, lettuce, dino kale, and collard starts all in a sunken cold frame hardening off to be planted in a couple weeks. My sunken cold frame seems to be anywhere from 5 to 10º F warmer than outside in the early morning. As I write this, it’s 8:30am on April 21st; the outside temp is 33º F and my cold frame is 42º F.
Gardening tasks and what to look out for in May
- Watch the weather. When nighttime temps stay in the 30s, a lot of cool-weather plants can go out and thrive. Take a peek at what we have outside of Greenhouse 5 to see what veggies are safe to put outside.
- Start seeds. Sunflowers, squash, beans, and corn all sprout fast and hate the cold. If you want to get a head start, or if the critters eat all your seeds when you plant them directly, start these plants in 4-inch pots. Transplant them into the ground once all chance of frost is gone and the nights are staying in the upper 40s. None of these plants like being root-bound, so timing is everything. If you start them too early, it might be more of a problem for you than starting them a little late. Don’t worry. I try to start these around mid-May at the earliest.
- Start a second round of things like leafy greens, cilantro, beets, and radishes. Leafy greens have a shorter life cycle than most veggies, so having a second sowing of arugula, lettuce, and spinach can help keep your cool season crops long lasting and delicious.
- Be ready for a surprise snow and/or frost up until June 1. The USDA Zone 5 lists May 15 as our last frost date, however if you check historical highs and lows for the area, around the beginning of June is a better date to go off of. I will say this is the warmest I’ve ever seen it this early, so I’m feeling a bit more willing to take a chance on some things. But last year I put my tomatoes out in early June and got a surprise cold spell that stunted them the one night I wasn’t home to cover everything in frost cloth. I’d like to get to mid-May and see what the extended forecast is like before I put out any frost-sensitive plants this year.
- Start thinking of watering. We had a bit of snow last year which was great for winter watering. If a plant is still totally dormant, it most likely doesn’t need much water right now, but if it's starting to put on a lot of new growth, give it a drink and see how it responds. If you notice it starts growing more vigorously after, be aware and start giving it supplemental water if we don’t get a lot of spring rainfall. Seedlings, plants in containers, and any perennial plant, shrub, or tree you're trying to get established will need more water than something that's dormant or already established.
- Stage plants in containers. What I do like to do with my perennial plants at this time of the year is stick them outside in their pots in the place I think I want to plant them. I’ll leave them there for weeks, making sure they get water, and it helps me both harden them off and decide whether or not the plant actually likes this spot before I stick it in the ground permanently. If a plant seems like it's suffering in the spot I picked, it’s time to assess and find a new spot.
- Plants can get too hot during the day if they’re covered or in a greenhouse. Make sure you're opening cold frames, hoop houses, and greenhouses during the day so you don’t cook your plants during the mid-day heat, and close them up in the evening before it gets too cold.
