Caring for spring bulb plants

As spring transitions to summer, many of our stalwart early blooming spring bulbs become afterthoughts in the flower beds and landscapes. However, their year is not quite yet complete — at least for most of the larger or later-blooming bulb plants, such as most tulips and many daffodils. If you want those bulbs to bloom well again next year, you need to make sure to properly care for them now, as well as the rest of the year.

The most important aspect of bulb care right now is to let the plants’ leaves yellow and die back naturally. Mowing or cutting them off while they are still green is going to hamper their ability to have stored enough energy to form full flower buds for next year, and it may lead to their eventual demise. Although a bit unsightly, these leaves must be left until dormant, if you want those plants to re-bloom properly. If you plan on replacing those bulbs with others, then you can certainly just dig and remove so they don’t take resources away from neighboring plants. Another aspect of care most years is to not let them get too dry, or they will go into induced dormancy more quickly than they really should.

Pest management is not quite as critical now as earlier, but you do want to maintain healthy plants as long as possible. Again, this is primarily to allow those bulbs to capture maximum energy and be able to overwinter easily and reward you with great blooms next spring. Keeping deer and rabbits away from tulips is probably one of the most important steps, as well as preventing chipmunks and squirrels from digging up or eating the bulbs. Foliar diseases may also impact your plants. These diseases may not be worth a fungicide application, but they will hasten leaf dieback. It is a good practice to cut off and remove disease-affected leaves as soon as they go dormant, so that you minimize the fungal inoculum that is present around the new growth when emergence occurs next spring.

If you are blessed with bulbs that are naturalizing and filling space too well, just after dormancy is one of the times when you can dig them up, divide the clumps, and move them or give them to other gardeners. You may also choose to mark the clumps and do this activity in the fall. Remember that the rule of thumb for planting depth is 2-3 times the height of the bulb. You can also store the bulbs until fall, keeping them in a cool, dry, consistent environment. Any new bulbs you want to acquire and have bloom in spring of 2021 also need to be planted between dormancy and fall. Planting date has some latitude, but the key is to have them planted early enough that they grow roots in the fall, otherwise their likelihood of overwintering properly is decreased.

Fall can be easier just for the reason that fall is the proper time to fertilize spring blooming bulbs, with a fertilizer that does not contain a lot of nitrogen (the first number on a fertilizer analysis). A balanced fertilizer is acceptable, or one that has more phosphorus and potassium, such as 9-23-30. Adding 1-2 tablespoons per 2 square feet of bulb area is about right, and you can consider adding bonemeal as a slow release phosphorus addition, at a rate of about ⅓ cup per 2 square feet. Do remember that the roots of these bulbs form at the base of the bulbs, and that is the depth at which bonemeal should be placed, and is also the best place for any fertilizers. You can also apply the fertilizer product over the top of the soil at those rates just as new growth emerges in the spring.

Alas, spring bulbs can have problems. One common issue is the bulbs not reblooming or surviving winter. That is more likely with cheaper, smaller bulbs. The adage of, “You get what you pay for” does come into play with spring bulbs. If you want longer-lived, larger-flowered plants, you are better served to buy higher quality, larger diameter bulbs direct from a producer. It is not uncommon to use swaths of bulbs to have an annual color pattern in a particular location. For this type of purpose, the cheaper bulbs are more of an option, as you are likely going to dig them up and dispose of them, anyway. Last point regarding selection is to think about your long-term goals. If you want patches of color, species tulips naturalize (multiply and spread a bit) much better than the hybrids and are better for most pollinators. The flowers are a bit smaller and on shorter stalks, but still offer brilliant color options and showiness.

Other issues that can cause a bulb to have leaf growth but no blossom is that they were originally planted too deeply, last year’s leaves didn’t have enough sunlight to produce enough storage energy, they are short on nutrients, they were damaged in some way or they had bulb/root rot due to excess soil water. If bulbs didn’t bloom and you don’t believe that a deer nipped off the buds or a sharp frost event killed the flower stalk, you may be best served to dig up and remove, or replant, the bulbs. After digging, examine the depth of planting to make sure that is correct, as well as the bulb size. If size has decreased and there are multiple bulbs, remove all the smaller bulblets and try replanting it properly. Think about sunlight in that spot and move them to an area where they will get good spring sunlight if that may be the issue. Good drainage is also a must, and some area gardens are facing elevated water levels that will make it difficult for bulbs to be in good shape going into next year.

If you have other questions about spring bulb care, or any other horticultural issue, you can contact Scott Reuss, UW-Madison Division of Extension Marinette County agriculture and horticulture agent. He can be reached at scott.reuss@wisc.edu or 715-732-7510. You can also find this and other horticulture management and pest management articles on the Marinette County Extension webpage, at https://marinette.extension.wisc.edu/horticulture/. One good publication regarding spring bulb care can be found at: https://web.extension.illinois.edu/bulbs/planting.cfm.